Evaluation of planned number of children, the well-being of the couple and associated factors in a prospective cohort in Yokohama (HAMA study): study protocol

Abstract

Introduction

Many developed countries including Japan are experiencing declining birth rates, particularly in urban areas. A gap between the planned number of children and the actual number of children exists, that is attributed to various factors such as: childcare leave and employment policies, childcare services, financial support, husbands’ contributions to household chores and childcare, marriage support, community, and couples’ well-being. Therefore, we propose HAMA study for having a baby, parenting, and marriage life (HAMA = ‘H’aving ‘A’ baby, parenting, and ‘MA’rriage life) in Yokohama (an urban area) to examine these issues.

Methods and analysis

In this large-scale cohort study, we will elucidate the actual situation of families and child-rearing in Yokohama, evaluate the current policies and propose future measures to prevent a decline in the birth rate. Overall, 10 000 young married couples (wives aged 20–39 years as of 2022) will be randomly selected, and a survey form will be sent to them annually. They will be followed-up for 5 years to examine the factors associated with the planned number of children, well-being of the couple, childcare support policies, externalisation of housework and childcare, fathers’ participation in housework and childcare, wives’ free time, loneliness and social connectedness, relationship with the spouse and if they are working, questions regarding their work style and work-life balance will also be included. Ultimately, a conceptual model of the planned number of children and associated factors will be developed.

Ethics and dissemination

This study has been approved by the Ethics Committee of Yokohama City University (reference number: 2022–10) and will be conducted following appropriate ethical guidelines. Opportunities to withdraw consent to participate in the survey are provided to participants. The results of this survey will be published as research papers in relevant journals and will be reported to the administration of Yokohama city and other agencies.

Strengths and limitations of this study.

• A large 5-year cohort study will be conducted in Yokohama, Japan, to identify factors contributing to the global challenge of declining birth rate, especially in urban settlements.

• This study will examine various factors contributing to the declining birth rate. Our research team comprises experts from diverse backgrounds, specifically business administration, economics, data science, paediatricians, obstetricians/gynaecologists and public health nurses.

• This study has been established with close collaboration with the administration of the city of Yokohama, which will enable the survey results to be feedback to the city’s administration and will be reflected in its policies.

• Although the subjects of this study will be randomly selected, there is a possibility of participation bias.

• Because of the high risk of bias owing to the questionnaire survey of self-reported data, a qualitative survey will also be conducted.

Introduction

Many developed countries, including Japan, are experiencing declining birth rates, particularly in urban areas. As of 2020, the total fertility rate was 1.33 in Japan, 1.64 in the USA, 1.58 in the UK, 1.53 in Germany, 1.82 in France and 1.66 in Sweden.¹ The birth rate is declining at an accelerating pace in the urban areas of Japan, with the total fertility rate tending to be low at 1.12 and 1.26 in Tokyo and Kanagawa prefectures (including Yokohama city), respectively. The Japanese population, which was 120 million in 2000, is expected to decline to 101.9 million by 2050 and to 59.7 million by 2100.² Several socioeconomic factors contribute to delays in childbearing. The lack of facilities such as affordable housing, flexible and part-time career options for women and affordable childcare have contributed to low fertility and birth rates. Couples delay starting a family, which causes a decline in their fertility levels because of ovarian ageing and associated reasons, leading to a reduced chance of conception.³

The declining birth rate will reduce population size not at all ages but only among the young. Low fertility produces an age structure that creates momentum for future population decline, which must be stopped for the population to remain demographically sustainable. A gap has been reported between the number of desired children and the actual number of children. In a survey conducted in Japan in 2015, the ideal number of children was 2.32 and the planned number was 2.01,⁴ which has been attributed to various factors such as financial support for the child, the age of childbearing because of later marriages, infertility and the psychological and physical burden of childcare. In Japan, the Basic Law on Measures for Society with a Decreasing Birthrate was implemented in 2003,⁵ in which support for childcare and work-life balance was promoted to combat the declining birth rate. However, the total fertility rate remains low, and further support for childrearing is necessary. In April 2023, a new Children and Families Agency was established to consolidate and implement policies for children’s welfare.⁶

Cohort studies focusing on fertility decline are currently being conducted globally. The Panel Study of Income Dynamics, being conducted in the USA since 1968, tracks household and individual income, education and labour market participation.^{7 8} In the UK, the British Birth Cohort Studies are being conducted, including four cohort studies on people born in 1946, 1958, 1970 and 2000.⁹ In Germany, the German Family Panel Survey has been conducted annually since 2010, surveying more than 10 000 families to determine their family life, financial situation and health status.¹⁰ A cohort study on declining fertility is being conducted in Japan. The Japan General Social Survey has been conducted since 2000 and includes various items related to life planning, family relationships and social support.^{11 12}

The following issues are considered indispensable for addressing the problem of declining birth rates: childcare leave and employment policies, childcare services, financial support, husbands’ contributions to household chores and childcare, marriage support and the community. Four main factors have been suggested to affect fertility rates. The first is work compatibility, which is discussed in terms of the relationship between the childcare leave system, shorter working hours, female employment rate and fertility rate.^{13 14} Yamaguchi¹⁵ investigated the impact of parental leave policies on women’s career and fertility choices and revealed both positive and negative effects.¹⁵ Second, childcare services should be enhanced.^16–18 Hwang et al (2015)¹⁹ suggest that enhanced childcare services can achieve two seemingly contradictory goals: increasing women’s labour force participation and increasing fertility. Third, economic support for the child-rearing generation is a measure to combat the declining birth rate.^{20 21} A study by Riphahn and Wiynck²² revealed that child allowance and tax reform in Germany showed a positive effect on fertility when high-income and low-income couples decided to have a second child. Fourth, a relationship between men’s participation in housework and childcare and the declining birth rate has been suggested.²³ McDonald²⁴ suggested that men’s participation in housework and childcare may lead women to have more children.²⁴ The declining fertility rate is a complex problem involving many factors. In addition, issues related to the declining birth rate unique to urban areas have been noted.^{25 26}

To the best of our knowledge, only a few studies have comprehensively examined the aforementioned factors, and studies focusing on urban areas are limited. Therefore, considering the differences in urban and rural regions, we propose the present HAMA study for having a baby, parenting and marriage life (HAMA=‘H’aving ‘A’ baby, parenting and ‘MA’rriage life) in Yokohama (an urban area) to examine the aforementioned factors. In this large-scale cohort study, we plan to elucidate the actual situation of families and parenting in Yokohama, evaluate policies and suggest future measures to prevent a decline in the birth rate.

Methods and analysis

Study design

This prospective cohort study will be conducted at a single centre, where a questionnaire survey will be carried out among married couples residing in Yokohama city. Ten thousand young married couples (wives born between 2 April 1983 and 1 April 2001, who have attained the age of 20–39 years in 2022) will be randomly selected, and a survey form will be sent to them by post. Two survey forms with the same survey items will be sent: one for the wives and one for the husbands, and each individual will be required to answer the survey form and submit it. The survey will have questions regarding satisfaction with life, health conditions, thoughts about children and the number of children, utilisation of time in routine, automation of housework, support for parenting, social connections and personal items. A return envelope will be enclosed with the form, and participants will have the option of sending their responses either by posting in the return envelope or by filling out the online form. These forms will be sent annually between December and February for 5 years. Each form will be assigned a household ID and identifier for men and women, allowing for easy follow-up. Major survey items, such as the well-being of the couple and the planned number of children, will continue to be included in the survey form to identify changes over time during the study period.

Inclusion criteria

Irrespective of whether the couple has children at the start of the survey, the inclusion criteria will be as follows:

1. Married couples residing in Yokohama city as of December 2022.

2. Wives aged between 20 and 39 years.

3. Families with children under 6 years old (preschoolers) or families without children.

Exclusion criterion

Couples who do not disclose their residential address will be excluded from the study.

Collection and assessment of data

Based on these criteria, 10 000 households will be randomly selected from the resident registration system of Yokohama city, which is maintained by the government, and the data will be made available for research of public interest. The first survey was sent to participants in January 2023 and responses were collected. To improve the collection rate, reminder postcards will be sent to participants: the first reminder postcard, about 3 weeks after sending the survey forms and the second reminder postcard, about 5 weeks after sending the survey forms.

A written explanation of the survey was provided with the first survey form. A check box will be provided on the survey form to confirm consent to the survey, and the checked box will be considered written informed consent. The completed survey forms with consent will be used for data analysis.

The questionnaire will include questions with reliability and validity from previous studies^27–32 and newly created questions. The questions regarding the planned number of children will be the same as those used in the Japanese government statistics. The well-being of the couple will be measured using a subjective analysis and the Gallup Index.³³ During the evaluation of childcare support policies, we will ascertain the awareness and use of current policies. The externalisation of housework and childcare will identify the external services used and the frequency of their use. Fathers’ participation in housework and childcare and wives’ free time will be used to measure husband and wives’ time and satisfaction with housework and childcare. Regarding loneliness and social connectedness, the social connectedness index developed in K6²⁷ and in previous studies^29–31 will be used. In addition, items related to the relationship between marital adjustment, parenting attitudes and family functioning for married and childbearing individuals, such as the Marital Adjustment Test, Family Assessment Device and Parent Attitude Research Instrument, respectively, will be used.

The questionnaire will also include items regarding household chores, such as the time spent on housework, childcare, sleep, the use of automation for housework (eg, dishwashers and robot vacuum cleaners) and household chores (eg, housekeeping and shopping services). Additionally, it will include questions for analysing relationships with the spouse and, if they are working, questions regarding their work style and work-life balance will also be included.

From a medical point of view, the questionnaire will include questions regarding children delivery methods, parents’ interest in painless delivery and satisfaction with access to perinatal and paediatric care and the healthcare delivery system. The health statuses of the children and parents will also be included in the questionnaire. The assessment plan that will be used for the analysis is presented in figure 1.

Figure 1.

Assessment plan used in the current study.

It has been indicated in the questionnaire and instruction document that responses to the survey questions are voluntary and that no one will be disadvantaged by not responding. The instruction document also clearly indicates that questions that the respondents do not want to answer should be omitted. Opportunities to withdraw consent to participate in the survey are also provided.

Primary endpoints

The primary outcomes of this study will be the planned number of children and couples’ well-being.

Secondary endpoints

The secondary endpoints of this study will be the evaluation of childcare support policies and wives’ free time. Additionally, the survey will determine the status of the externalisation of housework and childcare, husbands’ participation in housework and childcare and their sense of loneliness and social connectedness.

Data management

The collected data will be stored securely. The corresponding author will be responsible for data management and survey during the 5-year period. Other team members will have access to the raw data that do not contain personal information.

Patient and public involvement

Our study team includes researchers, paediatricians, obstetricians, gynaecologists, public health nurses and other members who are well-versed in the field. We consulted the Children and Youth Bureau of Yokohama city regarding the study design and questionnaire. They have been in contact with the child-rearing generation and are familiar with their challenges and problems. Their opinions will be reflected in this study. The main research method of the HAMA study is a questionnaire survey; however, we recognise the importance of further in-depth research through detailed interviews and group interviews with the parties involved. It is also necessary to administer this survey to couples in their 40s, who cannot be included in the study. Therefore, we plan to conduct further interviews with these individuals.

Sources of bias

One important bias is the consent bias. As this study will be conducted following ethical guidelines, we will exclude the data of individuals who do not provide consent. Additionally, response bias, which refers to several factors that can lead someone to respond falsely or inaccurately to a question, may occur. To avoid such biases, it is necessary to increase the response rate as much as possible. Therefore, we have chosen a sample size of 10 000 couples and prepared a dedicated website to disseminate information and gain trust.

Maintaining confidentiality

The collected data will be stored securely. The completed questionnaires will be kept in the study office at Yokohama City University. The collected survey data will not contain any identifiable personal information. Only a few members will have access to the survey form data. The data will be anonymised by excluding and encoding personal information. The processed data will be shared only with the research team, and the data linkage software will be adequately protected to maintain security and privacy.

Statistical analyses

Stratified analyses of income, education and residential area will be performed. Cross-sectional and longitudinal analyses will be performed on the data obtained in this study. We will analyse the correlations between each factor and perform a multiple or logistic regression analysis with the planned number of children and couple’s well-being as objective variables. In addition, a structural equation modelling will be used to examine the relationship between each factor. A longitudinal analysis will be used to analyse the relationship between changes in the planned number of children, the well-being of the couple and other factors. All analyses will be performed using the R software (R Foundation for Statistical Computing, Vienna, Austria), Stata (StataCorp LLC, College Station, Texas, USA), or SPSS (SPSS, Chicago, Illinois, USA).

Ethics and dissemination

This study has been approved by the Ethics Committee of Yokohama City University (reference number: 2022–10, dated 15 December 2022) and will be conducted following the appropriate ethical guidelines. The data collected in this study, excluding personal information, will be shared only with the study team members. The study team members will regularly attend ethics training sessions. Opportunities to withdraw consent to participate in the survey are provided to participants.

The results of this survey will be presented at academic conferences and published as research papers in relevant journals. Furthermore, the results will be reported to the administration of Yokohama city and other administrative agencies.

Discussion

This study will address an important issue about the declining birth rate in Japan’s urban areas. To the best of our knowledge, this will be the first study to elucidate the effect of various factors, such as childcare support policies, the status of outsourcing housework and childcare and husbands’ participation in household chores and childcare, on the planned number of children and the well-being of couples in Yokohama city.

Becker (1960)³⁴ proposed the following model for the optimal number of children:

$${\displaystyle n^{\ast }=\frac{Y+w\left(T+h+k\right)}{2\left(e+w\ast t\right)}}$$

where n* is the optimal number of children, Y is the husband’s income, w is the wife’s wage rate, T is the available time without the wife’s childcare assistance and h is the childcare support time of grandparents or husbands. This suggests that the determinants of the number of children are (1) income, (2) wife’s free time and (3) educational and childcare expenses and time, in addition to other factors (age at marriage, especially that of the wife). This model is a leading economic model for fertility and has been used in many recent studies.^35–39

However, Becher’s model is more than 60 years old and has undergone significant changes regarding way of life and values. Kögel⁴⁰ challenged the validity of the Becker model in explaining the relationship between fertility and female employment, suggesting that the association did not change over time in Organisation for Economic Co-operation and Development countries, contrary to what the model predicts. In addition, the model does not include factors relating to the husband, the wife’s employment status, the couple’s values and ideas and the well-being, loneliness and social ties of the couple. The present study will consider this model; however, we will construct a modified model that will reflect contemporary realities and urban characteristics.

After delivery, many women experience health issues that may necessitate a vacation from work. The likelihood of returning to work after maternity leave may be increased through structural interactions between supervisors and workers on maternity leave, supported by early medical advice from occupational physicians. To address this issue, the Mom@Work study has been proposed,⁴¹ where pregnant women who work at least 12 hours weekly for 1 of the 15 participating businesses will be enrolled. The managers of these expectant women will be randomly assigned to the intervention or control group, where those in the intervention group will be in touch with their employees during maternity leave and offer early support to the occupational physician. In the control group, the managers will not be structurally connected to their staff members during maternity leave. The Mom@Work study will provide important information regarding employees’ return to work after delivery. Additionally, the role of supervisors and occupational physicians in the successful return to work after childbirth will be clarified.

Another study⁴² has proposed two possible solutions from an occupational health perspective. First, companies should establish support systems to assist working women during pregnancy and childbirth. Such systems would require the cooperation and understanding of coworkers, including men, and the introduction of flexible work schedules designed to allow workers to care for family members with disabilities. Second, companies should guarantee workers the right to take sick leave and return to work, so that they can balance work with the need to treat chronic conditions.

Our study will help identify issues related to families and childcare in the urban areas of Japan with high population concentrations. The separate collection of data from husbands and wives will help identify their connectedness or disconnectedness. This study will build a conceptual model for the planned number of children after considering various factors that reflect contemporary realities and urban characteristics. Well-being will be used as an objective variable to identify associations with various factors such as parenting and marital relationships.

Our study has a limitation in that only self-reported data will be analysed, which may cause a high risk of bias. Qualitative research will also be conducted to identify aspects that could not be adequately elucidated in the questionnaire study.

In conclusion, the data generated from this study will contribute to policy planning and evaluation globally and in Japan through evidence-based policymaking for childcare support policies and measures to prevent declining birth rates.

Ethics statements

Patient consent for publication

Not applicable.