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Chapter 3 includes an assessment of the literature published within the last 30 years that addresses various health and health-related consequences of unintended pregnancy. The literature base for most consequences studied does not permit a numerical survey. However, some effects, particularly ones related to pregnancy and pregnancy outcome, have been studied sufficiently to permit a structured assessment. These consequences include timing of the initiation of prenatal care, an estimate of the adequacy of prenatal care based on both timing and the number of visits, exposure of the fetus to smoking and alcohol, and the incidence of low birthweight (<2,500 grams) among live-born infants. A graphical presentation of studies on these issues is provided in Chapter 3.
This appendix provides more detail regarding those studies. To be included in this structured assessment, an investigation had to compare outcomes between women reporting intended conceptions and women reporting unintended conceptions, variously defined. When unintended was subdivided into mistimed and unwanted, estimates of effects (usually odds ratios) are included for both categories of unintended conception. An odds ratio is an estimate of the relative risk, that is, the risk of a poor outcome among the "exposed" group (unintended conception) relative to the risk of a poor outcome among the "unexposed" group (intended conceptions). These results, with 95 percent confidence intervals, are shown in column 5 of the tables in this appendix. The results in Figures 3-3 through 3-5 of Chapter 3 were selected from these results. If a study calculated both a crude and an adjusted odds ratio, only the adjusted one was included in the figure. When the results were available for both mistimed and unwanted conceptions, they were included in the figures. The references for this appendix are provided in Chapter 3.
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D Tables of Odds Ratios: Supplement to Chapter 3
Carol J.R. Hogue
Member, Committee on Unintended Pregnancy
Chapter 3 includes an assessment of the literature published within the last 30 years that addresses various health and health-related consequences of unintended pregnancy. The literature base for most consequences studied does not permit a numerical survey. However, some effects, particularly ones related to pregnancy and pregnancy outcome, have been studied sufficiently to permit a structured assessment. These consequences include timing of the initiation of prenatal care, an estimate of the adequacy of prenatal care based on both timing and the number of visits, exposure of the fetus to smoking and alcohol, and the incidence of low birthweight (<2,500 grams) among live-born infants. A graphical presentation of studies on these issues is provided in Chapter 3.
This appendix provides more detail regarding those studies. To be included in this structured assessment, an investigation had to compare outcomes between women reporting intended conceptions and women reporting unintended conceptions, variously defined. When unintended was subdivided into mistimed and unwanted, estimates of effects (usually odds ratios) are included for both categories of unintended conception. An odds ratio is an estimate of the relative risk, that is, the risk of a poor outcome among the "exposed" group (unintended conception) relative to the risk of a poor outcome among the "unexposed" group (intended conceptions). These results, with 95 percent confidence intervals, are shown in column 5 of the tables in this appendix. The results in Figures 3-3 through 3-5 of Chapter 3 were selected from these results. If a study calculated both a crude and an adjusted odds ratio, only the adjusted one was included in the figure. When the results were available for both mistimed and unwanted conceptions, they were included in the figures. The references for this appendix are provided in Chapter 3.
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TABLE D-1 Studies of Prenatal Care Attainment Associated with Pregnancy Intention
Definition of Intention
Population/Sample
Retrospective/Prospective
Control Factors
Results
Reference/Comments
Initiation of Prenatal Care (PNC) after the First Trimester
Unwanted:
(a) at conception, (b) at fourth month,
(c) in last trimester
120 black women, Boston City Hospital, married with at least one living child, 1964
Prospective at three points during gestation
None
Late PNC, (a) ORa = 2.89 (0.96,9.02)c, (b) OR = 3.57 (1.38,9.36)c , (c) OR = 2.42 (0.65,9.31)c
Watkins, 1968; (a) 77.5%, (b) 27.9%, (c) 11.7%
(a) Mistimed, (b) unwanted
NSFG, 1982 (random sample of U.S. women 15–44, with live births 1979–1982)
Retrospective (œ3 yrs. postpartum)
Race
(a) RRb, all = 1.6c; RR, white = 1.6c; RR, black = 1.4c (b) RR, all = 1.8c; RR, white = 1.7c; RR, black = 1.75c
Pamuk and Mosher, 1988
"Intended" vs. "unintended"
NNS, 1980 (random sample of U.S., married)
Retrospective (>6 mo postpartum)
Race, residence, education, birth order
Crude OR = 1.25c Adjusted OR = -1.19c
Wells et al., 1987
Planned vs. unplanned
416, central Harlem residents in PNC, 1982–1983
Retrospective (at first PNC visit)
None
OR = 1.31c
McCormick et al., 1987; 73% were unplanned
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Definition of Intention
Population/Sample
Retrospective/Prospective
Control Factors
Results
Reference/Comments
Intended (stopped using contraception because of pregnancy desire or just before pregnancy, wanted to become pregnant) vs. unintended
NLSY, 1984, women 18–26, nationally representative sample of 6,015
Retrospective (78%), prospective (22% during pregnancy)
Race, economically disadvantaged (white), southern or urban resident at age 14, grandmother's education, maternal age
For unintended, crude RR = 1.14c; adjusted OR = 1.6c
Marsiglio and Mott, 1988; they used the term "wanted" but the questions more closely reflect intended
"Intended" vs. "unintended"
Random sample, 1,490; births in England, 1,984
Retrospective (>4 mo postpartum)
None
Risk of entry after first trimester; OR = 1.9 (1.33,2.17)c
Cartwright, 1988; interview asked pregnancy intention
(a) Mistimed, (b) unwanted
NMIHS, 1988 nationally representative sample of 9,953
Retrospective (at least 1 yr postpartum)
None
(a) RR = 2.88c (b) RR = 2.62c
Kost et al., 1994
(a) Mistimed, (b) unwanted
Oklahoma PRAMS, 1988–1993, (a) N = 2,329 (b) N = 933
Retrospective (4–12 mo postpartum)
Age, education, source of family income, timing of pregnancy recognition, parity
(a) Crude OR = 2.7 (2.1,3.4); adjusted OR = 1.4 (1.04,1.9) (b) crude OR = 4.6 (1.3,6.1); adjusted OR = 1.7 (1.1,2.5)
DePersio et al., 1994
Planned vs. "surprise"
Hispanic, Houston, TX, public hospital patients, 100 each entered PNC in 1st, 2nd, 3rd trimester or none
Retrospective (at delivery)
None
Risk of entry after first trimester OR = 2.64 (1.50,4.66)c
Byrd, 1994; early PNC associated with hospital access card, fewer perceived barriers, more benefits to baby
Inadequate Prenatal Care (PNC)
See Results column
Random sample in Oklahoma, births, 1985
Retrospective (at delivery)
Multiple
Receipt of inadequate care, mistimed, family support OR = 1.15c (NS); mistimed, pregnancy discussed OR = 1.09c (NS); unwanted, family support, OR = 1.15c (NS); unwanted, pregnancy discussed, OR = 1.36 (p < 0.05)
St. John and Winston, 1989; see text
Unwanted
Case—control study, three sites in Missouri; adequate, N=720; inadequate, N=764
Retrospective (at delivery)
Multiple
Receipt of inadequate care; OR = 1.39 (1.11, 1.67)
Sable, 1992; 74% of women with inadequate care had not wanted the pregnancy
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Complete Table on previous page.
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Definition of Intention
Population/Sample
Retrospective/Prospective
Control Factors
Results
Reference/Comments
Initial attitude: negative, mixed, or positive
200 poor, mainly black women, Detroit, MI
Retrospective (at delivery)
Attitudinal
Zero-order correlation = 0.39 (p < 0.05)
Poland et al., 1990
Planned vs. unplanned; somewhat/very unhappy vs. neutral/happy
Case—control, 400 inadequate care, 100 adequate care, Mecklenburg, NC, 1990–991
Retrospective (at delivery)
None
For unplanned, OR = 1.86 (1.10,3.18)c for unhappy, OR = 2.2 (0.96,3.70)c
Boggs and Miles, 1991; among cases with inadequate care, 81% unplanned and 21.2% unhappy
(a) Mistimed, (b) unwanted
Oklahoma PRAMS, 1988–1993 (a) N = 2,092 (b) N = 810
Retrospective (4–12 mo postpartum)
Education, marital status, source of family income, timing of pregnancy initiation, parity
(a) crude OR = 2.7 (1.9,3.7); adjusted OR = 1.3 (0.8,1.9) (b) crude OR = 5.5 (3.8,8.0); adjusted OR = 1.9 (1.2,3.1)
DePersio et al., 1994
NOTE: NSFG (National Survey of Family Growth); NNS (National Natality Survey); NLSY (National Longitudinal Survey of Youth); NMIHS (National Maternal and Infant Health Survey); PRAMS (Pregnancy Risk Assessment Monitoring System); NS (not significant).
a
The OR (odds ratio) is the odds of adverse outcome among exposed persons relative to the odds among unexposed persons.
b
The RR (relative risk) is the risk of the adverse outcome among exposed persons relative to the risk among unexposed persons. Relative risk and odds ratios are similar when adverse outcome is rare.
c
Calculated for this report.
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TABLE D-2 Studies of Behavioral Risk Factors for Low Birthweight or Preterm Delivery Associated with Pregnancy Intention
Definition of Intention
Population/Sample
Retrospective/Prospective
Control Factors
Results
Reference/Comments
Smoking
''Intended" vs. "unintended"
NNS, 1980 (random sample of U.S. married women)
Retrospective (> 6 mo post-partum)
Race, residence, education, birth order, early PNC
Whether didn't stop smoking: crude ORa = 1.13c; adjusted OR = 1.07c
Wells et al., 1987; early PNC had similar but independent impact on smoking cessation, as planning the pregnancy did
Planned vs. unplanned
416, central Harlem residents in PNC, 1982–1983
Retrospective (at first PNC visit)
None
OR = 1.08c
McCormick et al., 1987; 41% smoked during pregnancy
(a) Mistimed, (b) unwanted
NSFG, 1982 (random sample of U.S. women ages 15–44, with live births 1979–1982)
Retrospective (3 yr postpartum)
Race
(a) RRb, all = 1.3c RR, white = 1.25c RR, black = 1.05c (b) RR, all = 1.3c RR, white = 1.4c RR, black = 1.2c
Pamuk and Mosher, 1988
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Definition of Intention
Population/Sample
Retrospective/Prospective
Control Factors
Results
Reference/Comments
"Intended" vs. "unintended"
Random sample, 1,490; births in England, 1,984
retrospective (>4 mo postpartum)
Social class
Smoking OR = 1.66 (1.25,2.22)c
Cartwright, 1988; interview asked pregnancy intention
Intended (stopped using contraception because of pregnancy desire or just before pregnancy, wanted to become pregnant) vs. unintended
NLSY, 1984, women 18–26, nationally representative sample of 6,015
Retrospective (78%) and prospective (22% during pregnancy)
Race, economically disadvantaged (white), southern or urban resident at age 14, grandmother's education, maternal age
For unintended, crude RR = 1.04c; adjusted OR = 0.97c
Marsiglio and Mott, 1988; they used the term "wanted" but the questions more closely reflect intended
(a) Mistimed, (b) unwanted
NMIHS, 1988, nationally representative sample of 9,953
Retrospective (at least 1 yr postpartum)
Marital status
(a) Crude RR = 1.71c (b) crude RR = 1.47c
Kost et al., 1994; smoked during pregnancy; married women with wanted conception smoked much less than other subgroups
(a) Mistimed, (b) unwanted
Oklahoma PRAMS, 1988–1993 (a) N = 2,267 (b) N = 900
Retrospective (4-12 mo postpartum)
Age, education, race, martial status, source of family income
(a) Crude OR = 1.3 (1.02, 1.6); adjusted OR = 1.0 (0.8,1.3) (b) crude OR = 2.4 (1.9, 3.1); adjusted OR = 1.8 (1.3,2.4)
DePersio et al., 1994; smoking 3 mo before delivery
Alcohol
Planned vs. unplanned
416, central Harlem residents in PNC, 1982–1983
Retrospective (at first PNC visit)
None
OR = 2.67c
McCormick et al., 1987; 9.2% drank during pregnancy
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Definition of Intention
Population/Sample
Retrospective/Prospective
Control Factors
Results
Reference/Comments
Intended (stopped using contraception because of pregnancy desire or just before pregnancy, wanted to become pregnant) vs. unintended
NLSY, 1984, women aged 18-26, nationally representative sample of 6,015
Retrospective (78%), prospective (22% during pregnancy)
Race, economically disadvantaged (white), southern or urban residents at age 14, grandmother's education, maternal age
For unintended, crude RR = 1.05c; adjusted OR = 1.25c
Marsiglio and Mott, 1988; they used the term "wanted," but the questions more closely reflect intended
(a) Mistimed, (b) unwanted
NMIHS, 1988, nationally representative sample of 9,953
Retrospective (at least 1 yr postpartum)
None
(a) RR = 1.11c
(b) RR = 1.77c
Kost et al., 1994; drank one or more times per week
NOTE: NNS (National Natality Survey); NSFG (National Survey of Family Growth); NLSY (National Longitudinal Survey of Youth); PRAMS (Pregnancy Risk Assessment Monitoring System); NMIHS (National Maternal and Infant Health Survey).
a
The OR (odds ratio) is the odds of adverse outcome among exposed persons relative to the odds among unexposed persons.
b
The RR (relative risk) is the risk of the adverse outcome among exposed persons relative to the risk among unexposed persons. Relative risk and odds ratios are similar when adverse outcome is rare.
c
Calculated for this report.
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TABLE D-3 Studies of Low Birth Weight (LBW) (<2,500 grams) Associated with Pregnancy Intention
Definition of Intention
Population/Sample
Retrospective/ Prospective
Control Factors
Results
Reference/ Comments
Wanted vs. unwanted
17 selected U.S. sites, 1971–1972; 4,891 white and 3,030 black women
Retrospective (at delivery)
Race
Crude ORa = 1.2c OR for whites = 1.36c OR for blacks = 0.94c
Morris et al., 1973; women with high education and unwanted conceptions had babies with significantly higher LBW rates
Intended (stopped using contraception because of pregnancy desire or just before pregnancy, wanted to become pregnant) vs. unintended
NLSY, 1984, women ages 18–26, nationally representative sample of 6,015
Retrospective (78%) and prospective (22% during pregnancy)
Race, economically disadvantaged (white), southern or urban resident at age 14, grandmother's education, maternal age
For unintended, crude RRb = 1.3c; adjusted OR = 0.92c adjusted OR = 0.88c (including behavioral risk factors)
Marsiglio and Mott, 1988
(a) Mistimed, (b) unwanted
NSFG, 1982 (random sample of U.S. women aged 15–44, with live births 1979–1982)
Retrospective (œ 3 yr post-partum)
Race
(a) RR, all = 1.4c RR, white = 1.2c RR, black = 1.3c
Pamuk and Mosher, 1988
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Definition of Intention
Population/Sample
Retrospective/ Prospective
Control Factors
Results
Reference/ Comments
Unintended vs. intended
Case-control study, 1984; 83 LBW cases, 1,392 NBW controls
Retrospective (at delivery)
Smoking
Crude OR = 1.28c adjusted OR = 1.17c (0.70, 1.95)c
Cartwright, 1988
Wanted vs. unwanted
1,518 multiparous, indigent women in Birmingham, AL, 1985–1988, with risk of IUGR
Prospective (at PNC visit)
None
OR = 1.3c
Goldenberg et al., 1991; sample was limited to women receiving early PNC
Mistimed, unwanted
1988 NSFG, most recent singleton birth
Retrospective (< 5 yr post-partum)
Smoking, race
Reduction in LBW if all unwanted conceptions had been avoided
Kendrick et al., 1990; mistimed not associated with LBW
No.
% change
Black
69,000
7
White
67,000
4
Smoker
70,000
6
Non- smoker
66,000
7
(a) Mistimed, (b) unwanted
NMIHS, 1988, nationally representative sample of 9,953
Retrospective (at least 1 yr postpartum)
None
(a) Crude RR = 1.21c
(b) crude RR = 1.80c
Kost et al., 1994
(a) Mistimed, (b) unwanted
Oklahoma PRAMS, 1988–1993 (a) N = 2,215 (b) N = 888
Retrospective (4–12 mo postpartum)
Education, black race, marital status at delivery, smoking three months before delivery, trimester that PNC began, infant gender, parity, plurality
(a) Crude OR = 1.2 (1.1,1.4); adjusted OR = 1.0 (0.8,1.1) (b) crude OR = 1.4 (1.2,1.6); adjusted OR = 0.9 (0.7,1.1)
DePersio et al., 1994
(a) Mistimed, (b) unwanted
1990 NICHD/MOMIH survey
Retrospective (>6 mo postpartum)
Multiple
(a) No increased risk (b) crude OR = 1.44 for LBW adjusted or NS VLBW not associated
Sable, 1992
NOTE: NLSY (National Longitudinal Survey of Youth); NBW (Normal birthweight is over 2,500 grams); IUGR (intrauterine growth retardation); NSFG (National Survey of Family Growth); NMIHS (National Maternal and Infant Health Survey); PRAMS (Pregnancy Risk Assessment Monitoring System); NICHD/MOMIH (National Institute of Child Health and Development/Missouri Mothers and Infant Health); VLBW (very low birthweight is under 1,500 grams)
a
The OR (odds ratio) is the odds of adverse outcome among exposed persons relative to the odds among unexposed persons.
b
The RR (relative risk) is the risk of the adverse outcome among exposed persons relative to the risk among unexposed persons. Relative risk and odds ratios are similar when adverse outcome is rare.
c
Calculated for this report.
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Complete Table on previous page.
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