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. Author manuscript; available in PMC: 2017 Nov 1.
Published in final edited form as: Fertil Steril. 2016 Aug 1;106(6):1453–1462. doi: 10.1016/j.fertnstert.2016.07.1067

Pregnancy intentions – a complex construct and call for new measures

Sunni L Mumford a, Katherine J Sapra a, Rosalind B King b, Jean Fredo Louis c, Germaine M Buck Louis a
PMCID: PMC5159192  NIHMSID: NIHMS803878  PMID: 27490044

Abstract

Objective

To estimate the prevalence of unintended pregnancies under relaxed assumptions regarding birth control use compared with a traditional constructed measure.

Design

Cross-sectional survey.

Setting

Not applicable.

Patients

Nationally representative sample of U.S. females aged 15–44 years.

Intervention(s)

None.

Main Outcome Measure(s)

The prevalence of intended and unintended pregnancies as estimated by 1) a traditional constructed measure from the National Survey of Family Growth (NSFG), and 2) a constructed measure relaxing assumptions regarding birth control use, reasons for non-use, and pregnancy timing.

Results

The prevalence of unintended pregnancies was 6% higher using the traditional constructed measure as compared to the approach with relaxed assumptions (NSFG: 44%, 95% confidence interval [CI] 41, 46; new construct 38%, 95% CI 36, 41). Using the NSFG approach only 92% of women who stopped birth control to become pregnant and 0% of women who were not using contraceptives at the time of the pregnancy and reported that they did not mind getting pregnant were classified as having intended pregnancies, compared to 100% using the new construct.

Conclusion

Current measures of pregnancy intention may overestimate rates of unintended pregnancy, with over 340,000 pregnancies in the United States misclassified as unintended using the current approach, corresponding to an estimated savings of $678 million in public health care expenditures. Current constructs make assumptions that may not reflect contemporary reproductive practices and improved measures are needed.

Keywords: pregnancy intentions, unintended

INTRODUCTION

More than half of pregnancies in the United States are reported to be unintended (approximately 51%) (1–6), though a recent study reports a decline over the past several years with current rates being at a historic low of 45% (7). Unintended pregnancies include those that are mistimed, unplanned, or unwanted, and as such are quite broadly defined (1, 2, 8). Recent statistics suggest that efforts to reduce unintended pregnancy have been successful as measured by rates (7, 9). But measurement of the concept of pregnancy intention and what these statistics may indicate in light of the inherent limitations to current measurement approaches has not been thoroughly discussed (8, 10–18). As well, the public health implications of these declining rates are unclear when the evidence relating pregnancy intention to pregnancy outcomes is weak (9, 19–23).

Current definitions of intention assume that pregnancy is a conscious decision. However, given the complex emotional, psychological, and cultural factors at play, often behaviors do not align with intentions (10, 14, 24–26), and intentions may change over time (27–29). Indeed many women express ambivalence regarding their pregnancy intentions (30–33), and formulating plans for a pregnancy may seem unrealistic for many women as they do not perceive themselves as having reproductive control (34). Health care providers may also have different perspectives regarding whether a couple is prepared for a pregnancy (35–37), given that providers often want couples to conform to normative ideals regarding timing of pregnancy. Moreover, though the terms unplanned and unintended pregnancies are often used interchangeably, careful attention to terminology is important as the wording of questionnaires regarding pregnancy intention has been found to affect a woman’s assessment of her own pregnancy (38–40).

Given the complexities in measuring pregnancy intention, and the lack of broad application of new measures that more fully capture the multidimensional construct of pregnancy intention (e.g., timing, planning, wantedness, etc.) (10, 14, 41, 42), there is a need to understand how the assumptions underlying current measures may impact estimates of unintended pregnancies and whether varying constructs result in the same reliable estimate of unintended pregnancy. Thus, our objective was to estimate the prevalence of intended, mistimed, and unwanted pregnancies using the widely-cited traditional construct defined by the National Survey of Family Growth (NSFG 2006–2010) as compared to a constructed measure relaxing three assumptions regarding birth control use. Specifically, using the new measure: 1) women not using birth control because they wanted to become pregnant are now classified as intended regardless of the timing of the pregnancy; 2) women not using birth control but reported they did not mind becoming pregnant are now classified as intended; and 3) women who stopped using birth control to become pregnant are now classified as intended regardless of timing.

MATERIALS AND METHODS

Design and Study Population

The study population included 12,279 females ages 15–44 years who participated in the 2006–2010 cycle of the NSFG (43–45). The NSFG is designed to collect data from a national sample of reproductive-age women in the United States, and is based on a nationally representative, multistage, area probability sample drawn from 100 primary sampling areas (PSUs) across the country. Interviewing takes place on a continuous basis across the cycle, as field staff rotate each quarter across PSUs to generate a national representative sample over the course of the cycle. The overall response rate was about 78%. Details of the study design and survey assessments have been described in detail previously (44–46). The NSFG survey was reviewed and approved by the Research Ethics Review Board of the Centers for Disease Control and Prevention and the National Center for Health Statistics, and a similar board at the contracting organization at the University of Michigan (46).

Data Collection and Assessment of Pregnancy Intention

In-person interviews were conducted in households across the United States by trained interviewers using computer-assisted interviewing techniques for data collection. Information was obtained regarding contraception, infertility, marital status, pregnancy outcomes, and other health information (http://www.cdc.gov/nchs/nsfg/nsfg_questionnaires.htm).

For this study, the following definitions were used to define the prevalence of intended, mistimed (occurring sooner than the woman wanted), and unwanted pregnancies consistent with the format used for the NSFG constructed measure (2). Specifically, Figure 1 displays a simplified flowchart which outlines the participant flow for categorizing pregnancy intentions, and highlights where we relaxed certain assumptions for the new construct. Importantly, women are asked different questions regarding pregnancy intentions based on their previous responses to questions related to birth control use (which includes all forms of contraception including withdrawal, rhythm method, etc.) and these questions differ by the recency of the pregnancy (began within the past 3 years or longer than 3 years from the interview). As indicated by the first node on Figure 1, women are asked questions regarding their birth control use. Depending on whether they report birth control use the month of or the month after the pregnancy began they are then asked further questions. Women who did not report birth control use are then asked whether they were not using birth control with the intent to become pregnant. If women respond affirmatively, they are considered to have an intended pregnancy unless they report that the pregnancy occurred sooner than they anticipated (some of these women may later report that the reason why they did not use contraception was because they did not mind becoming pregnant). Only the women who were not using birth control but reported that they did not stop to become pregnant are asked if they ever wanted to have another baby. If they did not want another baby they are classified as unintended (some of these women may later report that the reason why they did not use contraception was because they did not mind becoming pregnant). If they respond that they did want another baby they are asked regarding the timing of the pregnancy to determine intention—if the pregnancy occurred too soon, it is unintended (some of these women may later report that the reason why they did not use contraception was because they did not mind becoming pregnant); otherwise it is intended. Of note, this classifies all pregnancies that occurred later than planned as intended.

Figure 1.

Figure 1

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NSFG construct of measurement of pregnancy intention modified to indicate how the new construct was created. Green text denotes the survey questions from the NSFG (2). Asterisks note where assumptions were relaxed for the new measure. Specifically, 1) women not using birth control because they wanted to become pregnant are classified as intended regardless of the timing of the pregnancy using the new measure (whereas the traditional NSFG measure asks additional questions regarding timing); 2) women not using birth control but reported they did not mind becoming pregnant are now classified as intended (whereas the traditional NSFG measure does not incorporate information regarding the reasons for not using birth control in this case); and 3) women who stopped using birth control to become pregnant are now classified as intended regardless of timing (whereas the traditional NSFG measure asks additional questions regarding timing).

Women who report birth control use for both the month of and the month after the pregnancy began are then asked follow-up questions regarding the type of method and if they ever wanted to have another baby. Further questions are then asked regarding the timing of the pregnancy to distinguish a mistimed pregnancy. Women who reported stopping birth control before pregnancy are then queried whether they stopped to become pregnant and if so whether the timing was too soon; those with pregnancies occurring too soon are unintended, otherwise intended. Only those women who report that they did not stop to become pregnant are asked directly whether they ever wanted another baby; those responding negatively are unintended while those responding affirmatively are asked about timing to determine intended or mistimed (unintended) pregnancies.

For our alternative approach, we relaxed three of the assumptions made in the previously described estimation of the prevalence of intended, mistimed, and unwanted pregnancies. These relaxed assumptions are noted by the asterisks in Figure 1. First, if women respond that they were not using a birth control method because they wanted to become pregnant then under the new construct we consider these pregnancies to be intended pregnancies (whereas NSFG asks further questions about timing and classifies any that happened too soon as unintended regardless of how many months or years too soon). Second, if women who were not using birth control reported that they did not ever want another baby but that they did not mind becoming pregnant, then they were considered to have an intended pregnancy (though a more apt description of these pregnancies may be ‘not unintended’, highlighting the nuance involved in any dichotomy used to classify pregnancy intention). Of note is that here we utilized information regarding the reasons for not using birth control, whereas the traditional NSFG construct does not use this information in this case. Third, if women reported that they had stopped birth control to become pregnant, they were classified as intended irrespective of the timing of the pregnancy.

In addition to the prevalence of intended, mistimed, and unwanted pregnancies, several alternative scales for the measurement of pregnancy intention were also assessed as described in the documentation for the NSFG (http://www.cdc.gov/nchs/nsfg/nsfg_2006_2010_puf.htm) (2). These included the trying scale (how much you were trying to get pregnant or avoid pregnancy), wanting scale (how much you wanted or did not want a pregnancy), and feeling scale (how happy or unhappy you were to be pregnant). The trying and wanting scales range from 0 to 10, and the feeling scale from 1 to 10, with higher scores indicating they were trying hard, wanted, and were very happy to become pregnant and lower scores indicating they were trying hard not to become pregnant, avoided pregnancy, and were very unhappy to be pregnant. These scales were also compared using both constructs as outlined above.

Statistical Analysis

Participant characteristics and contraceptive use characteristics were compared by pregnancy intention using both the traditional NSFG construct and a construct which relaxes several assumptions regarding intentions. The percent of unintended pregnancies and 95% confidence intervals (CI) by pregnancy outcome were also compared. Of note is that the NSFG traditionally reports pregnancy intention only among live births occurring within 5 years of the interview, and does not further provide breakdown by other pregnancy outcomes (2). The percent intended pregnancies for select characteristics were further evaluated by parity comparing the traditional NSFG construct with the new relaxed assumptions construct.

The mean of the trying, wanted, and feeling scales were also compared overall by pregnancy outcome, as well as by pregnancy intention status using both the traditional NSFG construct and the new relaxed construct. These measures are compared among all pregnancies, among live births, and among intended and unintended pregnancies occurring within 5 years of the interview. All estimates were corrected for the oversampling used in the survey design by using the sampling weights using SAS version 9.4 (SAS Institute, Cary, NC, USA).

RESULTS

We calculated that 32% (95% CI 29, 35) of live births were unintended, compared to 37% (95% CI 34, 40) reported in analyses using the NSFG methodology, and that only 14% (95% CI 12, 15) were classified as unwanted using both approaches (Table 1). Thus, overall 63% (95% CI 34, 40) of live births were intended using NSFG compared to 68% (95% CI 29, 35) using the new construct. Among all pregnancies, 38% (95% CI 36, 41) were unintended based on the new construct compared to 44% (95% CI 41, 46) by NSFG. The percentages of unintended pregnancies were similar across pregnancy outcomes, with the notable exceptions of current pregnancies which showed similar results as live births (NSFG: 36%, 95% CI 30, 42; new construct: 32%, 95% CI 26, 38) and terminations which showed much higher proportions of unintended pregnancies (NSFG: 93%, 95% CI 89, 96; new construct: 91%, 95% CI 87, 94). Moreover, the likelihood of a pregnancy being unintended decreased as age increased, and with increasing parity up to 2, with slightly lower rates estimated using the new construct (Table 1). Interestingly, a similar percentage of unintended pregnancies were reported among women who needed help getting pregnant (e.g., fertility treatment) using both constructs, likely due to the fact that this measure includes any use of fertility treatments in the past and not just for the index pregnancy. An important distinction between the two constructs is that in the NSFG 9% (95% CI 7, 10) of women who stopped birth control to become pregnant (64% of women who stopped birth control did so to become pregnant) were considered to have an unintended pregnancy as compared to 0% using the new construct. Most (55%) of the 9% unintended pregnancies using the NSFG construct were mistimed by less than 6 months. Another important distinction between the two constructs highlighted in Table 1 is that the new intention construct considers those that were not using contraceptives and report that they did not mind getting pregnant as having intended pregnancies (100% new construct vs 0% NSFG).

Table 1.

Comparison of pregnancy intention by participant characteristics using the traditional NSFG method and the new intention construct.

NSFG New Construct
Intended % (95% CI) Unintended % (95% CI) Mistimed % (95% CI) Unwanted % (95% CI) Intended % (95% CI) Unintended % (95% CI) Mistimed % (95% CI) Unwanted % (95% CI)
Weighted N in thousands 16722 12893 7733 5160 18318 11297 6243 5054
Overall 57 (54, 59) 44 (41, 46) 26 (24, 28) 17 (16, 19) 62 (59, 65) 38 (36, 41) 21 (19, 23) 17 (15, 19)
Pregnancy Outcome
 Livebirth 63 (60, 66) 37 (34, 40) 23 (21, 26) 14 (12, 15) 68 (65, 71) 32 (29, 35) 19 (17, 21) 14 (12, 15)
 Current Pregnancy 64 (58, 70) 36 (30, 42) 25 (20, 31) 10 (7, 14) 68 (62, 74) 32 (26, 38) 21 (16, 27) 10 (7, 14)
 Miscarriage 54 (49, 59) 46 (41, 52) 28 (24, 33) 18 (14, 23) 61 (56, 66) 39 (34, 44) 21 (17, 25) 18 (14, 22)
 Ectopic Pregnancy 59 (46, 72) 41 (28, 54) 23 (11, 35) 18 (7, 29) 62 (49, 76) 38 (25, 51) 20 (8, 31) 18 (7, 29)
 Stillbirth 53 (32, 75) 47 (25, 69) 31 (10, 51) 16 (0, 33) 74 (55, 93) 26 (8, 45) 10 (3, 17) 16 (0, 33)
 Terminations 7 (4, 11) 93 (89, 96) 46 (41, 52) 47 (41, 53) 9 (6, 13) 91 (87, 94) 45 (39, 50) 46 (40, 52)
Age at Interview, years
 15–19 13 (8, 17) 87 (83, 92) 68 (60, 76) 19 (13, 26) 19 (14, 24) 81 (76, 86) 62 (54, 70) 19 (13, 26)
 20–24 33 (28, 38) 67 (62, 72) 48 (44, 53) 19 (16, 23) 40 (35, 45) 60 (55, 65) 42 (37, 46) 18 (15, 22)
 25–29 55 (51, 59) 45 (41, 49) 27 (23, 30) 19 (15, 22) 61 (57, 65) 39 (35, 43) 21 (18, 24) 18 (15, 21)
 30–34 69 (65, 74) 31 (26, 35) 16 (13, 19) 15 (12, 18) 75 (70, 79) 25 (21, 30) 11 (8, 13) 15 (12, 18)
 35–39 72 (66, 77) 28 (23, 34) 13 (9, 16) 16 (12, 20) 76 (70, 81) 24 (19, 29) 9 (6, 12) 15 (11, 19)
 40–44 71 (64, 79) 29 (21, 36) 8 (4, 12) 21 (14, 27) 74 (67, 81) 26 (19, 33) 6 (2, 9) 21 (14, 27)
Parity
 0 33 (26, 40) 67 (60, 74) 51 (43, 58) 16 (11, 21) 40 (33, 47) 60 (53, 67) 44 (37, 51) 16 (11, 21)
 1 56 (52, 61) 44 (39, 49) 31 (28, 35) 13 (10, 15) 62 (58, 67) 38 (33, 42) 25 (22, 29) 12 (10, 15)
 2 63 (59, 68) 37 (32, 41) 22 (19, 25) 15 (12, 18) 68 (64, 73) 32 (27, 36) 17 (14, 20) 14 (12, 17)
 3 or more 55 (51, 60) 45 (40, 49) 20 (17, 24) 24 (20, 28) 60 (56, 65) 40 (35, 44) 16 (13, 19) 24 (20, 27)
Help getting pregnant 84 (80, 88) 16 (12, 20) 9 (6, 12) 7 (4, 10) 89 (85, 92) 11 (8, 15) 5 (3, 7) 6 (4, 9)
Stopped Birth Control to Become Pregnant 92 (90, 93) 9 (7, 10) 9 (7, 10) 0 (0, 0) 100 (100, 100) 0 (0, 0) 0 (0, 0) 0 (0, 0)
Ever Married 69 (66, 72) 31 (28, 34) 19 (16, 21) 13 (11, 15) 74 (71, 77) 26 (23, 29) 14 (12, 16) 13 (11, 15)
Currently Married 72 (69, 75) 28 (25, 31) 18 (15, 20) 10 (8, 12) 77 (74, 80) 23 (20, 26) 13 (11, 15) 10 (8, 12)
Cohabitating 43 (38, 48) 57 (52, 62) 35 (30, 39) 22 (19, 26) 49 (44, 54) 51 (46, 56) 29 (24, 34) 22 (18, 25)
Effectiveness of Primary Contraceptive Method (Among Women Using a Method)
 Most Effective 31 (8, 55) 69 (45, 92) 10 (2, 18) 59 (36, 82) 31 (8, 55) 69 (45, 92) 10 (2, 18) 59 (36, 82)
 Highly Effective 29 (24, 33) 71 (67, 76) 44 (38, 50) 28 (22, 33) 29 (24, 34) 71 (66, 76) 44 (38, 50) 28 (22, 33)
 Least Effective 31 (26, 37) 69 (64, 74) 40 (35, 45) 29 (25, 33) 32 (27, 37) 68 (63, 73) 39 (34, 44) 29 (24, 33)
Reason for No Contraceptive Use (Among Women Not Using a Method but Not Stopping to Become Pregnant)
 Didn’t expect to have sex 0 (0, 0) 100 (100, 100) 58 (47, 69) 42 (31, 53) 4 (1, 7) 96 (93, 99) 54 (42, 66) 42 (31, 54)
 Didn’t think could get pregnant 0 (0, 0) 100 (100, 100) 57 (48, 65) 44 (35, 52) 10 (4, 16) 90 (84, 96) 45 (37, 52) 46 (37, 54)
 Didn’t mind getting pregnant 0 (0, 0) 100 (100, 100) 87 (81, 93) 13 (7, 19) 100 (100, 100) 0 (0, 0) 0 (0, 0) 0 (0, 0)
 Worried about BC side effects 0 (0, 0) 100 (100, 100) 57 (45, 70) 43 (30, 56) 12 (1, 22) 88 (78, 99) 45 (32, 58) 43 (30, 56)
 Partner didn’t want responsibility to use BC 0 (0, 0) 100 (100, 100) 63 (46, 81) 37 (19, 54) 14 (2, 26) 86 (74, 98) 50 (31, 68) 37 (19, 54)
 Partner didn’t want to use BC 0 (0, 0) 100 (100, 100) 82 (71, 93) 18 (7, 29) 9 (0, 22) 91 (79, 100) 74 (57, 90) 18 (7, 29)
 Was using a method 0 (0, 0) 100 (100, 100) 53 (37, 68) 48 (32, 63) 2 (0, 4) 98 (96, 100) 51 (36, 66) 48 (32, 63)
 Could not get a method 0 (0, 0) 100 (100, 100) 80 (62, 97) 20 (3, 38) 0 (0, 0) 100 (100, 100) 80 (62, 97) 20 (3, 38)
 Not using method consistently 0 (0, 0) 100 (100, 100) 57 (44, 70) 43 (30, 56) 3 (0, 6) 97 (94, 100) 53 (40, 66) 44 (31, 57)
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BC, birth control; CI: confidence interval; NSFG, National Survey of Family Growth

We observed that the percent unintended also decreased as age increased for all levels of parity, with the lowest percentage of unintended pregnancies among those with one prior live birth (Table 2). Similar results were observed when comparing marital status and education by parity.

Table 2.

Percent unintended pregnancies for select characteristics by parity, comparing the traditional NSFG method and the new intention construct.

Parity = 0 Parity = 1 Parity = 2 Parity ≥ 3
NSFG New Construct NSFG New Construct NSFG New Construct NSFG New Construct
Age at Interview, years
 15–19 83 (72, 94) 76 (63, 88) 90 (85, 94) 86 (80, 92) 86 (76, 96) 79 (68, 89) 94 (81, 100) 67 (54, 80)
 20–24 84 (76, 92) 72 (63, 82) 63 (55, 71) 54 (46, 63) 63 (52, 73) 57 (47, 67) 70 (59, 80) 68 (57, 78)
 25–29 62 (47, 77) 56 (40, 71) 40 (34, 46) 36 (29, 42) 38 (31, 45) 32 (25, 38) 53 (47, 59) 47 (39, 54)
 30–34 55 (35, 75) 52 (31, 73) 20 (13, 27) 14 (8, 20) 27 (18, 37) 22 (13, 30) 37 (30, 43) 32 (26, 38)
 35–39 19 (1, 36) 19 (1, 36) 23 (10, 36) 15 (6, 24) 21 (13, 28) 18 (11, 26) 37 (28, 46) 33 (24, 42)
 40–44 18 (0, 37) 18 (0, 37) 12 (2, 21) 11 (1, 20) 26 (14, 38) 23 (13, 34) 40 (27, 53) 37 (23, 50)
Ever Married 38 (26, 50) 32 (21, 43) 26 (20, 32) 21 (15, 26) 26 (22, 30) 21 (17, 25) 39 (34, 43) 34 (29, 39)
Education at Interview
 Less than high school 65 (46, 83) 50 (24, 76) 41 (31, 51) 33 (23, 43) 50 (38, 61) 44 (32, 55) 48 (41, 56) 44 (36, 52)
 High school diploma/GED 62 (45, 79) 47 (28, 65) 44 (33, 56) 38 (26, 50) 39 (32, 46) 34 (28, 40) 49 (43, 55) 44 (37, 51)
 Some college 68 (53, 84) 63 (45, 81) 43 (32, 54) 36 (27, 46) 37 (26, 47) 34 (23, 44) 51 (43, 59) 48 (39, 56)
 College degree or more 47 (31, 63) 47 (31, 63) 19 (13, 24) 14 (9, 20) 19 (14, 24) 14 (10, 18) 26 (19, 34) 21 (14, 28)
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NSFG, National Survey of Family Growth

As anticipated, the trying, wanted, and feeling scales all differed by pregnancy outcome, with terminations receiving lower scores on all scales than the other outcomes (Table 3). Using the new construct, we observed lower mean values on all scores for pregnancies classified as unintended in comparison to intended pregnancies. Indeed, the difference in scores between intended and unintended pregnancies was larger using the new construct compared to the NSFG (trying scale: 5.09 versus 4.72; wanted scale: 6.10 versus 5.74; feeling scale 4.61 versus 4.26).

Table 3.

Trying, Wanted, and Feeling Scales for Measurement of Pregnancy Intention, by pregnancy outcome, and comparing the traditional NSFG method and the new intention construct.

Trying Scale
NSFG New Construct
Livebirth 5.78 ± 0.13 Intended 7.54 ± 0.11 7.45 ± 0.10
Termination 2.24 ± 0.22 On Time 7.48 ± 0.12 7.44 ± 0.10
Stillbirth 6.43 ± 1.03 Later 8.22 ± 0.20 6.03 ± 0.59
Miscarriage 5.67 ± 0.23 Unintended 2.82 ± 0.10 2.36 ± 0.09
Ectopic Pregnancy 5.72 ± 0.80 Unwanted 2.27 ± 0.14 2.17 ± 0.14
Current Pregnancy 6.15 ± 0.21 Too Soon 3.17 ± 0.14 2.52 ± 0.13
Wanted Scale
NSFG New Construct
Livebirth 6.18 ± 0.13 Intended 8.25 ± 0.10 8.03 ± 0.09
Termination 1.63 ± 0.26 On Time 8.20 ± 0.11 8.11 ± 0.10
Stillbirth 7.05 ± 0.91 Later 8.88 ± 0.16 7.18 ± 0.46
Miscarriage 5.77 ± 0.23 Unintended 2.51 ± 0.11 1.93 ± 0.10
Ectopic Pregnancy 6.44 ± 0.71 Unwanted 1.75 ± 0.15 1.62 ± 0.16
Current Pregnancy 6.52 ± 0.22 Too Soon 2.99 ± 0.15 2.18 ± 0.13
Feeling Scale
NSFG New Construct
Livebirth 8.01 ± 0.08 Intended 9.27 ± 0.05 9.14 ± 0.05
Termination 2.79 ± 0.18 On Time 9.30 ± 0.05 9.18 ± 0.05
Stillbirth 8.60 ± 0.54 Later 9.31 ± 0.13 8.54 ± 0.34
Miscarriage 7.13 ± 0.19 Unintended 5.01 ± 0.12 4.53 ± 0.12
Ectopic Pregnancy 7.52 ± 0.48 Unwanted 3.93 ± 0.17 3.82 ± 0.17
Current Pregnancy 8.06 ± 0.17 Too Soon 5.70 ± 0.15 5.09 ± 0.15
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Values are Mean ± SE.

DISCUSSION

Proper measurement of pregnancy intention is necessary for understanding its impact at the population level, and our findings empirically demonstrate that current approaches do not fully capture its multidimensional nature leading to the underestimation of intended and overestimation of unintended pregnancies. Specifically, we observed that the rate of unintended pregnancies decreased by 6% using a new construct which relaxed certain assumptions made in the NSFG as compared to the NSFG, which corresponds to a relative 12% decrease for all pregnancies. Our new categorization most often re-classified mistimed pregnancies as intended, highlighting the dependence of the NSFG construct on the relative timing of contraceptive use behavior and pregnancy, whereas the new construct places more emphasis on a woman’s categorization of her state of mind and reported actions.

We relaxed three assumptions, with each change based on prior evidence as outlined below (20, 30–34, 38, 47–50). First, we classified pregnancies to women who responded that they did not want another child but were not using birth control, and did not stop using contraception to become pregnant, but did not mind becoming pregnant as intended in the new construct. Much prior research has noted that in many cases women express ambivalence about their pregnancy intention (30–33, 38, 47). This ambivalence may stem from several reasons including expressing that planning is a not a salient concept (47), childbearing plans may not be fully formed, many women may not feel that they have reproductive control (34), having both positive and negative pregnancy desires (33), or their partners may also express ambivalence (30). It is becoming increasingly apparent that there is a need to evaluate the role of paternal intention in reproductive decisions as well (20, 30, 48, 49).

Next, we relaxed two assumptions related to contraceptive behavior and pregnancy timing. In particular, if a woman was either not using birth control or had stopped using birth control because she wanted to become pregnant, we considered these pregnancies to be intended regardless of how quickly the pregnancy came. In the NSFG construct, pregnancies that occur sooner than planned are classified as unintended, regardless of the length of the “mistiming,” which in some cases is as brief as a few months too soon (over 50% mistimed by less than 6 months) (50). In odd conceptual contrast, perhaps due to assumptions about concerns for infertility, pregnancies that occur later than planned are not considered mistimed although they are still happening at a time that was not what had been planned and may not be ideal, particularly if the couple had been trying for a long time.

The NSFG construct also appears to assume that positive preconception behaviors may not have been initiated (e.g. taking prenatal vitamins, abstaining from caffeine and alcohol, etc.) for pregnancies that occurred too soon, while conversely assuming that these behaviors remain constant over time once a woman begins “trying,” though it could also be reasoned that these behaviors may also change after enough time passes without the planned pregnancy. Given the complexities regarding intentions and contraceptive use, our new measure considered that all women who stopped birth control to become pregnant or who were not using birth control because they did not mind becoming pregnant had an intended pregnancy regardless of the timing.

A key aspect of measuring pregnancy intention under the NSFG construct is not only that women are not asked directly if the pregnancy was intended, but that not all women are asked the same basic questions about pregnancy intentions, as illustrated in Figure 1. Rather, different questions are asked of survey respondents based on their previous responses to questions on birth control use and pregnancy intention. What is not readily apparent on the simplified flowchart is that women who report that they “don’t know” if they would like to have another baby are asked many more questions in an attempt to further assess their pregnancy intentions as are women aged <20 years old. In fact, if all groups had been queried regarding “why no use” and “didn’t mind” (Figure 1), we may have seen even larger reductions in the percent unintended pregnancies using the new construct. The measurement of pregnancy intention, thus, becomes extremely complicated as different data regarding contraceptive use and non-use reasons are utilized in different cases.

Thus, depending on the respondent, the NSFG construct is derived from women’s responses to questions across domains of planning, contraceptive use behaviors, timing, and wantedness. Though intention and planning behaviors are thought to be expressed through contraceptive use behaviors, which are the basis for several of the assumptions in the NSFG construct, there is considerable discordance between intentions and behavior (10, 14, 24–26). Indeed, an extensive literature exists regarding the intricate and nuanced relationship between feelings and behavior towards pregnancy (8, 10, 13, 14, 17, 24, 25, 35, 51–54). Behaviors may thus rarely match intentions, and even among women with unintended pregnancies women report inconsistent contraceptive use behaviors and happiness over potential pregnancies (17, 54–56). This variation further points to the need for methods that distinguish between attitudes and behaviors, and as such questions regarding happiness and ambivalence were added to the NSFG (14). Interestingly, we observed that these scales were lower on average using the new construct, which suggest that the unintended pregnancies captured using the new construct were more appropriately classified. Moreover, the difference in scores between intended and unintended pregnancies was larger using the new construct compared to NSFG, which highlights perhaps the better discriminatory ability of the new construct.

Recent authors have called for new constructs that more fully capture the multidimensional nature of pregnancy intention (10, 12, 18, 38), especially as unintended pregnancies that are met with happiness may very well differ in terms of maternal and child health outcomes (9, 21, 50, 57–62). The London Measure of Unplanned Pregnancy is one such measure that has been validated in multiple populations (42, 63–67) that may offer promise for future studies. Other approaches that use variations of current approaches may also prove useful to further tease apart these effects (9, 10, 12, 22), as well as other questionnaires designed to capture a more nuanced assessment of pregnancy intention (12, 13, 41). Indeed, several studies have shown that outcomes tend to vary along a continuum of intended to severely mistimed to unwanted pregnancies. Specifically, increasing rates of low birth weight have been observed along this continuum from intended to mistimed (21, 61), and a recent meta-analysis reported increases in preterm birth only among unwanted but not mistimed pregnancies (62). These studies highlight that caution is needed when broadly interpreting evidence relating pregnancy intention to maternal and child outcomes as outcomes may differ depending on the nuances of the intention construct.

Indeed, one needs to be particularly careful when citing statistics regarding unintended pregnancies to clarify how the mistimed pregnancies were handled. The shift generated by our new construct corresponds to over 340,000 pregnancies (68) and 200,000 births per year in the United States (69) that are potentially misclassified as unintended, and a reduction in estimated public health care expenditures attributable to unintended pregnancies of $678 million based on previously published estimates of the cost differences of intended and unintended pregnancies (70–72). This change is also similar to the decline in unintended pregnancies observed over recent years that has been heralded as indicating success of interventions seeking to reduce unintended pregnancy (7).

It is also important to note that wantedness and pregnancy intention are typically assessed retrospectively. Once the child is born reflections on that time and ‘wantedness’ have been shown to change in other studies, especially given the terms we use to describe intention (11, 50), though we observed a similar prevalence of intention among both current pregnancies and live births but higher than pregnancies overall. Moreover, intention is typically reported only for live births, and there may be important differences by pregnancy outcome (particularly terminations). Understanding this difference in reporting intention only among live births is particularly relevant given the public health priority of preventing unintended pregnancies (73, 74). In moving forward, particularly as we try to assess the impact of unintended pregnancy on both maternal and child health outcomes, harmonization in the timing of assessment in relation to pregnancy is also an important goal.

In conclusion, we observed differences in estimates of the prevalence of intended and unintended pregnancies after relaxing various assumptions in the traditional NSFG construct for pregnancy intention. Current measures were observed to be sensitive to the underlying assumptions regarding birth control use patterns and intentions. Constructs are based on assumptions that may not reflect societal norms or contemporary practice underscoring the need for continual assessment of the measure. Misclassification of pregnancy intention may further result in erroneous conclusions regarding the associations between unintended pregnancies and adverse maternal and child outcomes which play an important role in developing policy. Depending on the application, these assumptions may be particularly relevant and the traditionally reported statistics may not be as useful as they could be for targeting interventions seeking to improve prenatal health care among women with unintended pregnancies.

Acknowledgments

This research was supported by the Intramural Research Program of the NIH, Eunice Kennedy Shriver National Institute of Child Health and Human Development. We would also like to thank Ya-Ling Lu at the NIH Library for her assistance with the figure.

Footnotes

Disclosures: None of the authors have a personal or financial conflict of interest.

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