Psychosocial Determinants of Intention to Use Dual Contraception Among Thai Female Students: Integrating the Health Belief Model and Theory of Planned Behavior

Abstract

Background

Dual contraception, the concurrent use of condoms and another effective method, is recommended for adolescents to prevent sexually transmitted infections (STIs) and unintended pregnancy. Identifying determinants of adolescent females’ intention to use dual contraception is essential for promoting sexual and reproductive health. This study integrates the Health Belief Model and the Theory of Planned Behavior and to examine influencing factors.

Objective

To identify determinants of intention to use dual contraception among female upper secondary school students in Thailand.

Methods

A cross-sectional study was conducted among 407 female upper secondary school students in Nonthaburi Province, Thailand. Data were collected using a researcher-developed questionnaire between November 2025 and January 2026. Statistical analyses included descriptive statistics, Chi-square tests, Pearson’s correlation coefficients, and multiple regression analysis. Statistical significance was set at p < 0.05.

Results

Overall intention to use dual contraception was high (M = 4.17, SD = 0.78). Eleven variables were significantly associated with intention (p < 0.05), including Grade Point Average, knowledge of dual contraception, personal life goals, subjective norms, perceived behavioral control, attitudes, perceived susceptibility, perceived severity of unintended pregnancy and STIs, perceived benefits, perceived barriers, and self-efficacy. Five factors significantly predicted intention, in descending order of predictive power: self-efficacy in dual contraception use (β = 0.395, t = 9.105, p = 0.000) perceived barriers to use dual contraception (β = −0.183, t = −4.743, p = 0.000); perceived severity of unintended pregnancy and STIs (β = 0.180, t = 3.497, p = 0.000); perceived susceptibility to risks of non-use (β = 0.121, t = 2.810, p = 0.005); and perceived behavioral control (β = 0.100, t = 2.234, p = 0.026). These variables jointly explained 61.60% of the variance in intention (Adjusted R² = 0.616, p < 0.05).

Conclusion

Intention to use dual contraception among female students was high and was significantly associated with personal, cognitive, and psychosocial factors derived from the integrated theoretical framework. The findings can inform the development of targeted interventions, adolescent-friendly services, and collaborative strategies to enhance informed decision-making and promote dual-method contraceptive use among adolescents.

Introduction

Dual contraception refers to an effective approach of birth control recommended by the World Health Organization for all populations, particularly adolescents.¹ The approach is to use a condom with another effective method of contraception, such as birth control pills, contraceptive implants, injections, and patches, or intrauterine devices (IUDs).² Dual contraception can prevent sexually transmitted infections (STIs) and also unintended pregnancies, particularly among adolescents who are not ready for pregnancy and are at higher risk of STIs.³ Therefore, if adolescents plan to have sex, dual contraception is recommended for the safety of both themselves and their partner.⁴ The consequences of pregnancy include health problems, namely premature birth, anemia, or serious complications, along with impacts on their education, future, quality of life, and family finances. Moreover, STIs can lead to infertility, stress, shame, and chronic diseases with long-term effects on adolescents’ lives.⁵

Regarding global pregnancy situation, the birth rate among women aged between 15 and 19 tended to decrease, but the problems were mostly found in many regions,⁶ particularly in low- and middle-income countries, where approximately 21 million pregnancies occurred annually, and more than half were unintended. In 2021, there were about 12.10 million pregnant teenage girls aged 15–19 and about 500,000 pregnant girls aged 10 to 14. The live birth rate in the 15 to 19 age group was highest in Africa, while the rate for girls aged 10 to 14 was highest in sub-Saharan Africa.⁷ Regarding sexually transmitted infections (STIs) among adolescents worldwide, more than 1 million STIs were cured daily.⁸ In the United States, the 15 to 24 age group accounts for half of the 20 million new STIs infections.⁹

In Thailand, adolescent pregnancy is a significant problem. Even though the birth rate among 15- to 19-year-old girls decreased, the birth rate among 10- to 14-year-old girls increased. Repeat pregnancies are also a significant issue, and 77.30%¹⁰ of unintended teenage pregnancies was caused by contraceptive failure. While the problem of adolescent pregnancy has begun to ease due to increased awareness among Thai teenagers about prevention, an unexpected problem has emerged, like the increase in sexually transmitted infections (STIs).¹¹ Moreover, STIs among adolescents increased, mainly due to unprotected sex.¹² The 15 to 24 age group had the highest incidence rate, and this tendency was not expected to change. The incidence rate of syphilis and gonorrhea among the 15 to 24 age group in Thailand increased from 104.70 per 100,000 population in fiscal year 2018 to 198.40 per 100,000 population in fiscal year 2023. The rates for syphilis and gonorrhea in the 15 to 24 age group in fiscal year 2023 were 91.20 and 86.70 per 100,000 population, respectively.¹² Therefore, preventing and addressing teenage pregnancy and sexually transmitted infections in Thailand are a significant problem that requires collaborative attempts from all sectors.

Nonthaburi Province, which is a suburban province to accommodate the expansion and growth from Bangkok, experienced ongoing community growth, leading to an “urban” society.¹³ Furthermore, the rate of teenage pregnancy increased compared to the previous year.³ In 2023, the birth rate among teenagers aged 10 to 14 years old was 0.80 per 1,000 teenagers aged 10–14 years old with a 52.50% increase from the previous year. The birth rate among teenagers aged 15 to 19 years old was 16.5 per 1,000 teenagers aged 15–19 years old with a 6.30%³ increase from the previous year. Additionally, sexually transmitted infections among teenagers were the most prevalent,¹⁴ with 50% of new infections in 15 provinces in 2023, including Nonthaburi.¹⁵ According to a disease situation report from the Digital Disease Surveillance Platform of the Epidemiology Division, Department of Disease Control, the incidence rate of sexually transmitted infections among adolescents aged 10 to 14 and 15 to 19 years old was 101.486 per 100,000 population, which is the highest in Health Region 4.¹⁴ Therefore, dual contraception can prevent both pregnancy and sexually transmitted infections (STIs) as recommended by the World Health Organization.¹ This study aimed to identify related factors to gain useful knowledge for promoting adolescent health. This study placed a focus on studying the predictors of intention to use dual contraception among female high school students in Nonthaburi Province through an integrated framework from the Theory of Planned Behavior (TPB)¹⁶ and the Health Belief Model (HBM)¹⁷ to comprehensively analyze related factors influencing intention to use dual contraception. Along with a literature review, the predictors of these factors can be categorized as: Personal factors, including academic achievement, personal life goals, and knowledge on dual contraception; factors from the TPB, including subjective norms in using contraception, perceived behavioral control in dual contraception use, and attitudes towards dual contraception; and factors from the HBM, including perceived susceptibility of not using dual contraception, perceived severity of pregnancy and STIs, perceived benefits of dual contraception use, perceived barriers to use dual contraception and perceived self-efficacy in dual contraception use. However, although the Theory of Planned Behavior (TPB) and the Health Belief Model (HBM) have been widely used in previous studies, each framework has limitations when applied independently. The Theory of Planned Behavior (TPB) focuses on cognitive and social influences on intention but may not fully capture individual perceptions of health risks and benefits, whereas the Health Belief Model (HBM) emphasizes individual beliefs but may not adequately address social and normative influences. Therefore, relying on a single theoretical framework may limit a comprehensive understanding of the factors predicting Thai female adolescents’ intentions regarding dual contraceptive use.

A literature review on factors predicting intention to use dual contraception among adolescents showed that most studies used mixed methods, focusing either on the use of one contraceptive method or on a single conceptual framework or theory. This led to incomprehensiveness of variables and factors in the theoretical framework. Furthermore, integration between health theories and concepts was limited. Studies employed the Theory of Planned Behavior,^18–21 the Health Belief Model,^22,23 or personal factors namely knowledge, attitudes, and practices.^24,25 The results focused on investigating the relationship between theoretical factors and contraceptive behavior,^26–30 risky sexual behavior,^31–33 choice of contraceptive services,³⁴ or factors influencing intention or behavior towards pregnancy and pregnancy prevention.^23,35,36 Intention to use dual contraception was mainly studied among lower secondary school students.³⁷ For research sample, most studies chose university students^{18,22,29,35,38} and vocational students,^36,39,40 Teenage mothers aged^{21,23,41–44} or groups of teenagers at risk or already infected with STIs.^34,45 Also, female high school students in their late adolescence, who reached maturity and can decide their own righteous path,⁴⁶ if they intend to use dual contraception, can increase their decision to use dual contraception.¹⁶ This can prevent teenage pregnancy and sexually transmitted diseases. To address these gaps, this study introduces a novel methodological approach by integrating constructs from the Health Belief Model (HBM) and the Theory of Planned Behavior (TPB) into a unified framework, incorporating a comprehensive set of variables derived from the literature review to assess adolescents’ intentions regarding dual contraceptive use. This approach is grounded in both theoretical frameworks and empirical evidence. Additionally, this study applies validated measurement scales within the sociocultural context of Thailand, thereby extending existing theoretical applications and providing new insights into contraceptive decision-making among Thai female adolescents. Therefore, the findings of this study can be used by relevant agencies to inform the development of appropriate activities and policies that effectively influence female adolescents’ decisions regarding dual contraceptive use.

Materials and Methods

This study is a cross-sectional study with an objective to investigate the predictors of dual contraception intention among high school female adolescents in Nonthaburi Province, Thailand. Multistage sampling was employed. Descriptive statistics including frequency, percentage, mean, and standard deviation, Chi-square test, Pearson’s correlation, and multiple regression were employed to analyze the findings.

Study Population and Samples

The population of this study includes 10,427 female students in grades 10 to 12 in schools under the Nonthaburi Secondary Educational Service Area Office.⁴⁷

The sample of this study consists of 407 female students in grades 10 to 12 from schools under the Nonthaburi Secondary Educational Service Area Office. The multistage sampling was employed to ensure representativeness. In the first stage, schools were selected using stratified random sampling. In the second stage, classrooms were randomly selected, and all eligible female students within the selected classrooms were invited to participate. In the third stage, the number of female students in each grade level to obtain an appropriate sample size for the research, using domain name calculation and probability (Proportional to Size – PPS). Next stage, Classrooms in each grade level will be randomly selected from the schools randomly selected within each inter-school district using simple random sampling, representing 50% of the total number of classrooms, through a selection without replacement method and Last stage female students from each grade level were randomly selected using simple random sampling with a non-replacement method. The sample was chosen from the student numbers of the female students in each classroom until the required number of students for the research was determined.

The sample size was calculated using Daniel’s population size estimation formula⁴⁸ with a standard value under the normal curve at a 95% reliability (2-tailed) of 1.96 and a p-value of 0.65. This standard value was derived from Patuma’s study³⁹ of female vocational students who used dual contraception during sexual intercourse in the past six months. The referenced population is comparable to the present study, as female vocational students were in a similar adolescent age group and have comparable behavioral characteristics to female high school students. Although Daniel’s population size estimation formula⁴⁸ was developed for simple random sampling, it was used to obtain an initial sample size estimate, and a multistage sampling design was subsequently applied to enhance representativeness. In this study, the initial sample size calculation was 338.38 students, equivalent to 339 students. To ensure a sample and prevent incomplete responses, the sample size increased by 20%⁴⁹ or 67.80 students, equivalent to 68 students. Therefore, the total sample size is 407 students.

Research Instruments

The instrument in this study was a questionnaire developed by the researcher, consisting of 4 parts and 56 items. This questionnaire’s content validation was conducted by three experts, namely an expert in health education and behavioral sciences, an expert in health and reproductive health, and an expert in health promotion. Importantly, this instrument was designed to incorporate constructs from both the Theory of Planned Behavior (TPB) and the Health Belief Model (HBM) within a single questionnaire, organized into distinct sections. This approach enables a more comprehensive assessment of factors influencing female adolescents’ intentions regarding dual contraceptive use, compared with previous studies that have typically applied only a single theoretical framework. The details of the instrument are as follows:

(1) A questionnaire on personal factors consists of 14 items, including 3 general information questions as closed-ended checklist answers; an 8 items of knowledge test on dual contraception with 4-choice multiple choice question (MCQ) answers (1 point for a correct answer and 0 points for an incorrect answer), with 3 levels of interpretation: poor knowledge (0–4 points), moderate knowledge (5–6 points), and high knowledge (7–8 points).⁵⁰ The index of item objective congruence (IOC) was from 0.67 to 1.00, and the reliability was analyzed using the Kuder-Richardson 20 (KR-20) with a try-out value of 0.70. Also, there were 3 items of personal life goal questions with 5 levels of interpretation: completely agree, strongly agree, moderately agree, disagree, and strongly disagree. The interpretation was also on 3 levels: high (3.68–5.00), moderate (2.34–3.67), and low (1.00–2.33).⁵¹ The IOC was from 0.67 to 1.00, and the Cronbach’s alpha coefficient from the try-out was 0.687.

(2) A questionnaire on the Theory of Planned Behavior consists of 14 items, including subjective norms in using contraception, perceived behavioral control in dual contraception use, and attitudes towards dual contraception. Each has five options: completely agree, strongly agree, moderately agree, disagree, and strongly disagree. The interpretation has three scales: high (3.68–5.00), moderate (2.34–3.67), and low (1.00–2.33).⁵¹ The IOC was from 0.67 to 1.00, and the Cronbach’s alpha coefficient from the try-out was 0.897.

(3) The questionnaire on the Health Belief Model consists of 23 items, including perceived risk of not using dual contraception, perceived susceptibility of not using dual contraception, perceived benefits of dual contraception use, perceived severity of pregnancy and STIs, perceived barriers to use dual contraception, and perceived self-efficacy in dual contraception use. Each has five options: completely agree, strongly agree, moderately agree, disagree, and strongly disagree. The interpretation has three scales: high (3.68–5.00), moderate (2.34–3.67), and low (1.00–2.33).⁵¹ The IOC was from 0.67 to 1.00, and the Cronbach’s alpha coefficient from the try-out was 0.956.

(4) A questionnaire on intention to use dual contraception consists of 5 items with 5 options: completely agree, strongly agree, moderately agree, disagree, and strongly disagree. The interpretation has 3 scales: high (3.68–5.00), moderate (2.34–3.67), and low (1.00–2.33).⁵¹ The IOC was from 0.67 to 1.00, and the Cronbach’s alpha coefficient from the try-out was 0.855.

Data Collection

In this study, data were collected from a consenting research participant who met the inclusion criteria, namely female high school students (Grades 10 to 12) studying at schools under the Nonthaburi Secondary Educational Service Area Office, enrollment for at least one semester, and voluntarily providing truthful information along with parents’ consents with signed consent forms. Data were collected using questionnaires during the academic term, November 2025 to January 2026. A letter requesting permission to collect data was sent to the school director after receiving ethical approval from the Mahidol University’s Human Ethics Committee. A meeting was held with the school administrators and homeroom teachers of the sample to introduce the researcher and explain the objectives and details of the study. After obtaining permission from the school administrators, the researcher distributed consent forms to the research sample for review and discussion before they decided to participate. The researcher also requested consent forms to be submitted for the research sample to be signed by their parents, and a date was scheduled for data collection. The consent forms were returned on the day of data collection. Data collection was conducted with a research sample taking about 30 to 40 minutes to complete the questionnaire.

After the sample completed the questionnaire, the researchers checked the accuracy of the data and analyzed it. The response rate of the study was 100%, based on the number of completed questionnaires returned. Data collection was conducted under the supervision of the researchers to ensure standardized administration and minimize potential bias during questionnaire completion. Participants were informed that their responses would remain confidential and that teachers would not have access to individual responses, thereby reducing social desirability bias. Incomplete or inconsistent questionnaires were excluded from the analysis, as described above. These procedures were implemented to ensure data quality and consistency with standard research practices. The results were published overall without personal information disclosed. In addition, data validation procedures were performed prior to data analysis. All returned questionnaires were checked for completeness and consistency, and incomplete or inconsistent responses were excluded. The data were then coded and entered into statistical software, and accuracy was verified through double-checking and data cleaning procedures. The validated dataset was subsequently used for statistical analysis.

Data Analysis

Data analysis was conducted using a validated and cleaned dataset to ensure the accuracy and reliability of the results. This study analyzed data using descriptive statistics, including frequency, percentage, mean, and standard deviation. General data were analyzed using the Chi-square test, Pearson’s correlation coefficient, and multiple regression analysis. A statistical significance level of 0.05 was set. Before analysis, the following statistical assumptions were looked at as follows: (1) The Chi-square test discovered that both variables were measured on a nominal scale, and the sample size was sufficient with an expected number (frequency) of no less than 5.⁵² (2) Correlation shows that the variables were measured on a ratio scale with a normal distribution, and the relationship between the variables was linear, and each pair of data was independent.⁵³ and (3) Multiple regression analysis consists of (3.1) the dependent variable, which was intention to use dual contraception and was measured at the interval scale; (3.2) the independent variables, which were related to intention to use dual contraception and included personal factors, demographic data, namely academic achievement in the latest semester, knowledge on dual contraception, and personal life goals; factors based on the Theory of Planned Behavior, including subjective norms in using contraception, perceived behavioral control in dual contraception use, and attitudes towards dual contraception; and factors from the Health Belief Model, including perceived susceptibility of not using dual contraception, perceived benefits of dual contraception use, perceived severity of pregnancy and STIs, perceived barriers to use dual contraception, and perceived self-efficacy in dual contraception use; (3.3) the independent and dependent variables with a high linear relationship; (3.4) the assessment of normality using histogram and Kolmogorov–Smirnov (p = 0.000) and Shapiro–Wilk tests (p = 0.000), indicating that the data were not normally distributed; however, regression assumptions were further evaluated based on residual diagnostic; (3.5) homoscedasticity was assessed through visual inspection of residual plots; (3.6) the independent variables which must not have multicollinearity; and (3.7) the predictive and dependent error margins which were independent. The Durbin Watson was 1.985. The tolerance was between 0.477 and 0.503, and the VIF was between 1.577 and 2.812.⁵⁴

Ethical Considerations

In this study, ethical approval for human research was obtained from the Faculty of Public Health, Mahidol University, in compliance with the Declaration of Helsinki (COA No. MUPH 2025–168, November 25, 2025). The researchers met with the research participants for introduction and explained the objectives, methodology, data collection methods, and the rights of the participants to participate or refuse participation without affecting their academic performance or scores. If the parents of the participants and the participants themselves agreed to participate, they had the right to withdraw from the study at any time without any reason stated. Data are analyzed and published in overall only and kept confidential. No identification, names, or personal information that can be traced back are disclosed. Data presentation is in overall, and the researcher will destroy any data after the study is published.

Results

The findings are divided into three parts: (1) intention to use dual contraception; (2) the relationship between personal factors, factors from the TPB, factors from the HBM, and intention to use dual contraception; and (3) the predictive power of personal factors, factors from the TPB, and factors from the HBM on intention to use dual contraception.

Intention to Use Dual Contraception

Regarding intention to use dual contraception among female high school students in Nonthaburi Province, most of the sample had a high level of intention to use dual contraception (70.30%), followed by a moderate level (29.50%), and a low level (0.20%), with a mean score of 4.17 (SD = 0.78). Details divided according to the three factors are as follows:

Regarding personal factors, (1) general demographic data showed that 407 samples were mostly studying in grade 12 (46.68%), followed by grade 11 (35.14%), and grade 10 (18.18%). The majority of grade point average (GPA) was greater than or equal to 3.50 (56.26%), followed by 3.00–3.49 (28.50%), 2.50–2.99 (12.78%), and less than 2.50 (2.46%). The most were in the science-mathematics program (55.28%), and the arts-language program (44.72%). (2) General data on knowledge about dual contraception showed that most of the sample had a moderate level of knowledge on dual contraception (5–6 points) (47.90%), followed by a high level of knowledge (7–8 points) (29.70%) and a poor level of knowledge (0–4 points) (22.40%), with an average score of 5.54 points (SD = 1.60, Min = 0, Max = 8). (3) General data on personal life goals showed that the sample had personal life goals at a high level (79.10%), a moderate level (18.40%), and a low level (2.50%), with an average of 4.33 (SD = 0.72), as shown in Table 1.

Table 1.

Demographic Data (n = 407)

Demographic Data	Frequency	%
Grade level
Grade 10	74	18.18
Grade 11	143	35.14
Grade 12	190	46.68
Grade point average (GPA)
Greater than or equal to 3.50	229	56.26
3.00–3.49	116	28.50
2.50–2.99	52	12.78
Less than 2.50	10	2.46
Study plan
Science-Mathematics program	225	55.28
Arts-Language program	182	44.72
Knowledge about dual contraception
High level of knowledge	121	29.70
Moderate level of knowledge	195	47.90
Poor level of knowledge	91	22.40
Personal life goals
High level of personal life goals	322	79.10
Moderate level of personal life goals	75	18.40
Low level of personal life goals	10	2.50

Factors from the TPB revealed that the sample’s level of opinion on the intention to use dual contraception, based on factors from the TPB, including subjective norms in using contraception, perceived behavioral control in dual contraception use, and attitudes towards dual contraception had details as follows:

Subjective norms in using contraception were mostly at a high level, with a mean score of 4.19 out of 5 (SD = 0.69). The most sample (80.60%) had a high level of agreement, followed by a moderate level (18.70%), and a low level (0.70%).

Perceived behavioral control in dual contraception use had a mean score of 4.26 out of a 5 (SD = 0.71). The most sample perceived their behavioral control in dual contraception use at a high level (79.60%), followed by a moderate level (19.20%), and at a low level (1.20%).

Attitudes towards dual contraception had a mean score of 4.22 out of 5 (SD = 0.74). The most sample (75.20%) had a high level of attitudes towards dual contraception, followed by a moderate level (24.10%) and a low level (0.70%), as shown in Figure 1.

Figure 1.

Level of the Intention to Use Dual Contraception from the Theory of Planned Behavior’s Factors.

Factors related to the HBM influenced the sample’s opinion on their intention to use dual contraception. These factors included perceived susceptibility of not using dual contraception, perceived benefits of dual contraception use, perceived severity of pregnancy and STIs, perceived barriers to use dual contraception, and perceived self-efficacy in dual contraception use. Details are as follows:

Most of the sample had the opinion on the perceived susceptibility of not using dual contraception at a high level, with a mean score of 4.08 out of 5 (SD = 0.75). About 70.30% of the sample had a high level of perceived susceptibility of not using dual contraception, followed by 28.00% who at a moderate level and 1.70% at a low level.

Most of the sample had the opinion on perceived benefits of using dual contraception at a high level, with a mean score of 4.36 out of 5 (SD = 0.81). About 76.90% of the sample had a high level of perceived benefits of using dual contraception, followed by 21.90% at a moderate level, and 1.20% at a low level.

Most of the sample had the opinion on the perceived severity of pregnancy and STIs at a high level, with a mean score of 4.36 out of 5 (SD = 0.78). About 76.40% of the sample had a high level of perceived severity of pregnancy and STIs, followed by 22.90% at a moderate level, and 0.70% at a low level.

Most of the sample had the opinion on perceived barriers to use dual contraception at a high level, with a mean score of 3.74 out of 5 (SD = 1.01). About 57.30% of the sample had a high level of perceived barriers to use dual contraception at a high level, followed by 34.30% at a moderate level, and 8.40% at a low level.

Most of the sample had the opinion on perceived self-efficacy in dual contraception use at a high level of perceived self-efficacy, with a mean score of 4.12 out of 5 (SD = 0.87). About 67.60% of the sample had a high level of perceived self-efficacy in dual contraception use, followed by 30.50% at a moderate level, and 2.00% at a low level, as shown in Figure 2.

Figure 2.

Level of the Intention to Use Dual Contraception from Health Belief Model’s Factors.

The Relationship Between Personal Factors, Factors from TPB, Factors from HBM, and Intention to Use Dual Contraception

The analysis of relationship between personal factors, factors from TPB, factors from HBM, and intention to use dual contraception among high school students in Nonthaburi, Thailand, showed that:

For personal factors, demographic information, namely grade level ( = 1.746, p = 0.418) and program ( = 3.762, p = 0.052), were not related to intention to use dual contraception. However, the latest semester’s GPA was related to intention to use dual contraception ( = 9.129, p = 0.028), as shown in Table 2. The results showed that knowledge on dual contraception had a weak positive correlation with intention to use dual contraception with a statistical significance of 0.05 (r = 0.230, p = 0.000). Similarly, personal life goals had a moderate positive correlation with intention to use dual contraception with a statistical significance of 0.05 (r = 0.385, p = 0.000). Moreover, knowledge on dual contraception and personal life goals were analyzed using Pearson’s correlation coefficient, which is described in the HBM as a relevant variable in both personal variables and the HBM.

Table 2.

The Relationship Between Personal Factors, Factors from Theory of Planned Behavior, Factors from Health Belief Model, and Intention to Use Dual Contraception

Demographic Data	Intention to Use Dual Contraception			p-value
	Moderate–Low (%)	Good (%)
Grade level			1.746	0.418
Grade 10	19 (25.70)	55 (74.30)
Grade 11	48 (33.60)	95 (66.40)
Grade 12	54 (28.40)	136 (71.60)
The latest semester’s GPA			9.129*	0.028
Greater than or equal to 3.50	55 (24.00)	174 (76.00)
3.00–3.49	43 (37.10)	73 (62.90)
2.50–2.99	18 (34.60)	34 (65.40)
Less than 2.50	5 (50.00)	5 (50.00)
Study plan			3.762	0.052
Science-Mathematics program	58 (25.80)	167 (74.20)
Arts-Language program	63 (34.60)	119 (65.40)

Note: * indicates p < 0.05.

Factors from the TPB, namely subjective norm in using dual contraception (r = 0.459, p = 0.000), perceived behavioral control in dual contraception use (r = 0.526, p = 0.000), and attitudes towards dual contraception (r = 0.597, p = 0.000), were statistically significant at 0.05.

Factors from the HBM, including perceived susceptibility of not using dual contraception (r = 0.580, p = 0.000), perceived severity of pregnancy and STIs (r = 0.654, p = 0.000), perceived benefits of dual contraception use (r = 0.679, p = 0.000), perceived barriers to use dual contraception (r = −0.501, p = 0.000), and perceived self-efficacy in dual contraception use (r = 0.701, p = 0.000), were statistically significant at 0.05, as shown in Table 3.

Table 3.

Results of Correlation Analysis (n = 407)

Variables	1	2	3	4	5	6	7	8	9	10	11
1. Intention to use dual contraception.	1	0.230*	0.385*	0.459*	0.526*	0.597*	0.580*	0.654*	0.679*	−0.501*	0.701*
2. Knowledge on dual contraception		1	0.335*	0.356*	0.257*	0.328*	0.231*	0.252*	0.280*	−0.336*	0.234*
3. Personal life goals			1	0.572*	0.376*	0.528*	0.250*	0.351*	0.416*	−0.482*	0.295*
4. Subjective norm in using dual contraception				1	0.502*	0.640*	0.387*	0.449*	0.475*	−0.418*	0.428*
5. Perceived behavioral control					1	0.627*	0.554*	0.612*	0.509*	−0.271*	0.583*
6. Attitudes towards dual contraception						1	0.502*	0.675*	0.656*	−0.556*	0.549*
7. Perceived susceptibility of not using dual contraception							1	0.768*	0.655*	−0.293*	0.600*
8. Perceived severity of pregnancy and STIs								1	0.814*	−0.389*	0.684*
9. Perceived benefits of dual contraception use									1	−0.524*	0.653*
10. Perceived barriers to use dual contraception										1	0.336*
11. Perceived self-efficacy in dual contraception use											1

Note: * indicates p < 0.05.

The Predictive Power of Personal Factors, Factors from the TPB, and Factors from the HBM on the Intention to Use Dual Contraception

The analysis found five independent variables that significantly predicted the intention to use dual contraception among high school students in Nonthaburi, Thailand, at a statistical significance of 0.05. These variables, arranged by standardized regression coefficient, included perceived self-efficacy in dual contraception use (X1) (β = 0.395, t = 9.105, p = 0.000), perceived barriers to use dual contraception (X2) (β = −0.183, t = −4.743, p = 0.000), perceived severity of pregnancy and STIs (X3) (β = 0.180, t = 3.497, p = 0.000), perceived susceptibility of not using dual contraception (X4) (β = 0.121, t = 2.810, p = 0.000), and perceived behavioral control in dual contraception (X5) (β = 0.100, t = 2.234, p = 0.000). These five factors predicted 61.60% (Adj.R²) of the variance in the intention to use dual contraception among high school students in Nonthaburi with statistical significance of 0.05. Considering the direction and weight of the correlation between the predictor variables, a positive correlation was found, with the predictive equation in raw score form = (1.287) + 0.354(X₁) - 0.142(X₂) + 0.180(X₃) +0.125(X₄) +0.105(X₅) and the predictive equation in standardized score form Z = 0.395Zx₁ - 0.183Zx₂ + 0.180Zx₃ + 0.121Zx₄ + 0.100Zx₅ as shown in Table 4.

Table 4.

Regression of the Predictive Power of Personal factors, Factors from the Theory of Planned Behavior, and Factors from the Health Belief Model on the Intention to Use Dual Contraception (n = 407)

Predicting Factors	b	SE (b)	β	t	p-value
1. Perceived self-efficacy in dual contraception use	0.354	0.390	0.395	9.105*	0.000
2. Perceived barriers to use dual contraception	−0.142	0.030	−0.183	−4.743*	0.000
3. Perceived severity of pregnancy and STIs	0.180	0.052	0.180	3.497*	0.000
4. Perceived susceptibility of not using dual contraception	0.125	0.045	0.121	2.810*	0.005
5. Perceived behavioral control in dual contraception	0.105	0.047	0.100	2.234*	0.026

Notes: R = 0.788, R² = 0.621, Adj.R² = 0.616, S.E. (est) = 0.48, df = 5, F = 131.199,

Durbin-Watson = 1.985, Constant = 1.287. * indicates p < 0.05.

Discussion

Intention to Use Dual Contraception

This study examined the intention to use dual contraception and discovered that the sample had a high level of intention to use dual contraception (M = 4.17, SD = 0.78). Several factors may influence this level of intention among female high school students in Nonthaburi. Nonthaburi’s ongoing community expansion led to its urbanization with the presence of numerous major government offices.¹³ Therefore, the sample had a certain level of access to health information and activities, both through the education system where affiliated teachers received training in sex education and life skills through the online sex education teacher development program in fiscal year 2023⁵⁵ and through proactive public health systems from agencies, namely the Department, Provincial Administrative Organizations, and Provincial Public Health Offices that jointly promote and drive sexual and reproductive health for teenage pregnancy prevention.⁵⁶ In this study, the sample was high school students studying in schools under the Nonthaburi Secondary Education Service Area Office, including a process for driving online sexuality education in all schools, called a 6-step process namely: (1) Scan: Survey data of teachers and administrators to register for online sexuality education training through the online sexuality education program; (2) Strategies: Define guidelines for promoting sexuality and life skills learning management through online sexuality education training through online workshops to promote and develop the quality of sexuality education management for administrators and pilot teachers; (3) Start: Supervise and follow up online sexuality teachers who completed the training to implement the process into teaching, conduct supervision, follow up and evaluate the teaching management of sexuality education; (4) Participate: Participation of administrators, teachers and educational supervisors in supervising, following up and evaluating the teaching management of online sexuality education, promoting and supporting schools and teachers responsible for teaching sexuality education to plan lessons to cover all students in the school, and all 6 aspects must be covered, including human development, relationship, personal skills, sexual behavior, sexual health, and social and culture; (5) Performance: Promote teachers to achieve good performance and learning management using sexuality as a base and (6) Promote: Promote reporting of results of sexuality learning management online, publicize and be selected at the educational district level as a representative of outstanding teachers for the project to promote sexuality education and life skills learning management in schools.⁵⁵

In addition to policies about gender issues in educational institutions, the public health sector and women and family development centers also prioritize gender issues in schools and communities, leading to students learning about and learning sex education and life skills.⁵⁷ This led to a high level of intention to use dual contraception. Compared to previous studies, a study on intention to use dual contraception among junior high school students in Chonburi showed a high level of intention.³⁷ The intention to prevent premature pregnancy among female high school and vocational school students in Khanu Woralaksaburi District, Kamphaeng Phet Province, was also at a high level.³⁶ The level of intention to use contraceptive implants among pregnant women in the upper southern region was at a moderate level.²³ A study of adolescents in Uganda found intention to use contraception at a high level, but the actual use rate was low due to social context.⁵⁸ Similarly, a study on factors influencing contraception decisions among adolescents in Malawi found that adolescents’ decisions to choose contraception were influenced by multiple levels of social factors.⁵⁹

The Relationship Between Personal Factors, Factors from TPB, Factors from HBM, and Intention to Use Dual Contraception

However, although most studies found a high level of intention among adolescents to use dual contraception, varying intention may occur depending on the social context and actual practice due to differences in the dependent variables in the studies, which focused on intention to prevent pregnancy or use different types of contraception, as well as cultural and social characteristics. Also, the sample with varying priorities and different geographical locations can affect comparisons. Factors that could potentially predict the intention to use dual contraception among female high school students in Nonthaburi Province are as follows:

Perceived self-efficacy in dual contraception use can significantly predict the intention to use dual contraception among female high school students in Nonthaburi at a statistical significance level of 0.05 (β = 0.395, p = 0.000). Studies directly examining perceived self-efficacy in dual contraception use among female high school students were limited, but studies focused on various aspects of adolescent self-efficacy in contraception use such as a study on perceived self-efficacy in dual contraception use among female vocational students in Chonburi Province, showing that it could predict dual contraception use.³⁹ Perceived self-efficacy in contraception was positively correlated with contraceptive behavior among female vocational students and jointly predicted contraceptive behavior among female vocational students³⁹ in Bangkok⁴⁰ and the upper southern region.²⁶ Similarly, studies on the use of prescription contraceptives showed higher rates in the group with high perceived self-efficacy.⁴⁵ This is according to adolescent behaviors that encourage risk-taking and challenging themselves to test their own power against society but overlook problems.⁴⁶ Therefore, empowering adolescents to use dual contraception could boost their self-efficacy and encourage them to be confident in using contraception. This can be explained by the fact that perceived self-efficacy in dual contraception use helped adolescent girls become aware of and reduce potential anxiety or obstacles from deciding to use dual contraception. Therefore, those with high perceived self-efficacy were more likely to confidently choose and use dual contraception than those with low perceived self-efficacy, which aligns with the Health Belief Model,² which defines perceived self-efficacy as an expectation of achieving a certain outcome that leads to a specific goal.

Perceived barriers to use dual contraception significantly predicted the intention to use dual contraception among high school female students in Nonthaburi at a statistical significance of 0.05 (β = −0.183, p = 0.000). Although studies on perceived barriers to accessing dual contraception were limited, studies on barriers among adolescent mothers showed that those who perceived side effects of oral contraceptives as a barrier tended to use oral contraceptives less often.⁴² Studies also investigated that perceived barriers to HIV and AIDS prevention behaviors at a high level had a negative impact on these behaviors.²² Similarly, experiences of barriers to contraception were correlated with the use of prescription contraceptives.⁶⁰ This suggests that if female adolescent perceived barriers to accessing dual contraception, they would unconsciously engage in cost-benefit analysis.⁶¹ Discomfort or obstacles can also affect disease prevention behaviors.⁶² In this context, cooperative behavior in disease prevention is the use of dual contraception, which aligns with the Health Belief Model,¹⁷ which defines perceived barriers as beliefs about obstacles from practices or negative impacts. Perceived barriers can become obstacles to the implementation of recommended behaviors. Since perceived barriers affected the intention to use dual contraception, it indicates that all sectors involved in providing contraception, including condoms and other modern contraception, should minimize barriers to access for adolescents. If adolescents perceive barriers to accessing dual contraception, such as waiting times, costs, secrecy, and difficulty finding services, they may view dual contraception as a barrier and reduce the use.

Perceived severity of pregnancy and STIs could significantly predict the intention to use dual contraception among high school female students in Nonthaburi with a statistical significance of 0.05 (β = 0.180, p = 0.000). Although studies on the severity of pregnancy and STIs were limited and did not cover both perceived severity of pregnancy and STIs, other studies have addressed perceived severity in various aspects, such as perceived severity of pregnancy complications.⁴⁴ This is in line with studies on the perceived severity of adolescent pregnancy, which can predict pregnancy and the promotion of positive health behaviors among pregnant adolescents.⁴³ Perceived severity of AIDS and pregnancy could predict sexual behavior.¹⁹ Perceived severity influencing healthy pregnancy behaviors in adolescent girls could be explained by the fact that adolescents are in the development stage for the future and developing self-esteem, which is a development of mental and intellectual aspects.⁴⁶ This influences social development, such as the development of behavior patterns for survival expressed definitively in adolescents.³⁰ Furthermore, perceived severity and impacts of pregnancy and STIs led to the perception that pregnancy and STIs are threats according to the Health Belief Model,¹⁶ which defines perceived severity of disease as beliefs, feelings, and assessments of health impacts in terms of physical severity, disease transmission, self-improvement, and a positive effect on disease prevention behaviors. Therefore, relevant sectors in providing knowledge and understanding about the severity of adolescent pregnancy and the impact of STIs should conduct public awareness campaigns, including recommending dual contraception. Accurate information should be provided in the adolescent environment, such as schools, homes, or online social media for adolescents to access anytime and anywhere.

Perceived susceptibility of not using dual contraception significantly predicted the intention to use dual contraception among female high school students in Nonthaburi at statistical significance of 0.05 (β = 0.121, p = 0.000). This is consistent with studies on perceived susceptibility of STIs and pregnancy, which found that these factors could predict dual contraception use.³⁹ Perceived susceptibility of unwanted pregnancy was positively correlated with contraceptive behavior,⁴⁰ as well as perceived susceptibility of not using condoms or contraception leading to STIs testing.28 This is in line with the Health Belief Model,¹⁷ where individual acceptance or rejection of the susceptibility of STIs varies,⁶⁸ requiring beliefs and expectations about risk to directly influence adherence to health recommendations.63 Since perceived susceptibility of not using dual contraception affected the intention to use dual contraception, communicating the impacts of adolescent pregnancy and STIs to adolescents and helping them to analyze the cost-effectiveness of dual contraception made this perceived susceptibility a beneficial factor and a driving force in deciding to use dual contraception, even if they already have a high level of intention to use it.

Perceived behavioral control in dual contraception use significantly predicted the intention to use dual contraception among female high school students in Nonthaburi of a statistical significance of 0.05 (β = 0.100, p = 0.000). Perceived behavioral control is a key factor in behavior development according to the Theory of Planned Behavior.¹⁶ Current research on perceived behavioral control in dual contraception use, such as contraceptive implants, shows that perceived behavioral control in contraception implants was the best predictor²³ and could significantly predict condom use behavior.¹⁸ Perceived behavioral control posed a direct positive influence on condom use behavior, along with intention.³⁰ Furthermore, a high level of perceived behavioral control was related to the highest level of control over contraception use among postpartum women in rural Uganda.⁵⁸ Perceived behavioral control was an individual’s perception of whether certain control factors facilitate or impede the behavior.⁵ Since perceived behavioral control in dual contraception use influenced the intention to use dual contraception, it is key to increase the ease and reduce the difficulty of accessing and using dual contraception. Promoting awareness of control over dual contraception among female adolescents could develop their intention into a behavior of using dual contraception. This is in line with the Theory of Planned Behavior¹⁶ which defines perceived behavioral control as a key factor in behavior development. Beliefs about control may be influenced by past experiences, observations, anecdotal evidence, or perceptions of ease of access and the ability to facilitate or impede the behavior.

This study discovered that four variables from the Theory of Planned Behavior (TPB) and the Health Belief Model (HBM) could collectively predict intention to use dual contraception. Also, one variable from the Health Belief Model could predict intention to use dual contraception. This demonstrates that integrating the TPB and the HBM can predict intention to use dual contraception, in line with the study in China on proactive health behaviors that applied TPB and the HBM,⁶³ the study in Malaysia, which integrated the TPB and the HBM to study healthy behaviors in married couples,⁶⁴ the study in Iran, which applied study to study COVID-19 prevention behaviors,⁶⁵ and the study in Italy, which also employed the TPB and the HBM.⁶⁶ Significantly, this study contributes novel evidence by identifying psychosocial determinants of dual contraceptive intention among Thai female students using a combined theoretical approach. While previous studies have applied either the Theory of Planned Behavior (TPB) or the Health Belief Model (HBM) independently, this study demonstrates the value of examining both frameworks within a single analysis. This approach provides a more comprehensive understanding of female adolescents’ decision-making processes, particularly in the context of dual contraceptive use, which has been relatively underexplored in prior research. Moreover, this study identifies specific predictive factors across both theoretical frameworks, providing a clearer understanding of how cognitive, social, and perceptual factors influence Thai female adolescents’ intention to use dual contraception.

The study discovered that the level of intention to use dual contraception among female high school students in Nonthaburi was mostly high. This creates an opportunity for educational and public health agencies, as well as relevant adolescent networks, to develop innovative activities to promote adolescent decision-making on dual contraception. Apart from existing knowledge enhancing and memory review activities, it is crucial to further educate adolescents about the susceptibility of not using dual contraception, including the impacts of pregnancy and STIs. Publicizing access to dual contraception services for adolescents is also essential to enhance their self-efficacy and perceived behavioral control in dual contraception use and reduce barriers to access. Furthermore, communication and awareness campaigns about dual contraception should be encouraged and implemented through adolescents’ social circles, such as friends, family, and partners, to create an environment conducive to their decision-making. However, limitations of this study include its urban context, making it inaccurate and irrelevant to the entire population. Further studies in semi-urban or rural contexts are needed to compare findings on dual contraception intention. Additionally, the questionnaire was done by the sample, and given the nature of sexuality and contraception, some respondents may have felt embarrassed due to the relatively limited openness regarding sexuality in Thai society.

Conclusion

This study found that the level of intention to use dual contraception among female upper secondary school students was high, reflecting awareness and recognition of sexual health and contraceptive practices to prevent unintended pregnancy. Factors associated with intention to use dual contraception included personal and theoretical constructs. Among personal factors, demographic characteristics such as most recent grade point average (GPA) were associated with intention. Knowledge of dual contraception showed a low-level association, while personal life goals demonstrated a moderate association. Regarding constructs of the TPB, subjective norms related to contraceptive use showed a moderate association with intention. Perceived behavioral control over dual contraceptive use and attitudes toward dual contraception demonstrated strong associations. For constructs of the HBM, all factors showed strong associations with intention, including perceived susceptibility to the consequences of not using dual contraception, perceived benefits of dual contraceptive use, perceived severity of unintended pregnancy and sexually transmitted infections, perceived barriers to accessing dual contraception, and self-efficacy in using dual contraception. Five factors significantly predicted intention to use dual contraception among female upper secondary school students: perceived self-efficacy in using dual contraception, perceived barriers to accessing dual contraception, perceived severity of unintended pregnancy and sexually transmitted infections, perceived susceptibility to the consequences of non-use, and perceived behavioral control over dual contraceptive use. Overall, these findings directly address the research objectives by identifying both the level of intention to use dual contraception and the key predictive factors influencing this intention among Thai female upper secondary school students. Therefore, these findings can inform the development of targeted interventions and policies to promote dual contraceptive use among female adolescents.

Funding Statement

This study did not receive any specific funding from public, commercial, or non-profit funding agencies.

Abbreviations

GPA, grade point average; HBM, Health Belief Model; IOC, index of item objective congruence; IUDs, intrauterine devices; MCQ, multiple choice question; STIs, sexually transmitted infections; TPB, Theory of Planned Behavior.

Data Sharing Statement

All data produced or examined in this study are contained within this published article.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.