Whether women who spend time in jail while pregnant are at increased risk of poor birth outcomes may depend on their age. Infants born to women in Washington State who were incarcerated and in their 30s during pregnancy weighed significantly less at birth than did those born to a comparison group of women who were not incarcerated; for infants whose mothers were 40 or older, however, the relationship was reversed. Those born to women in their 30s who spent time in jail also had significantly elevated odds of being low-birth-weight or being preterm. No association between birth outcomes and incarceration was evident for younger women.1
To study relationships between incarceration during pregnancy and birth outcomes, researchers compared data on 496 singleton births to women who had been detained in a King County jail while pregnant in 1994-1998 with data on 4,960 births to Medicaid recipients who had not been incarcerated. The groups were matched according to the proportions of mothers who were white, were aged 25 or older, had had more than one birth, abused substances and smoked. After comparing characteristics of the groups in bivariate analyses, the researchers used linear and logistic regression to identify associations between incarceration and birth weight, low birth weight, preterm birth and small size for gestational age.
Most of the women who had spent time in jail had been incarcerated for minor offenses. Three-quarters had been detained only once while pregnant; the median stay in jail during pregnancy was 14 days, but the range was wide (1-254 days). Half had entered jail during their first trimester, and only one in 10 in their third.
In both the study and the comparison groups, four in 10 births were to 18-24-year-olds, nearly half to women aged 25-34, one in 10 to women in their late 30s and a negligible proportion to women 40 or older. Half of births in each group were to white women; however, a significantly larger proportion of babies born to detained women than of those in the comparison group had black mothers (34% vs. 19%). Incarcerated women had less schooling and lower socioeconomic status than comparison women. Receipt of prenatal care before the third trimester was less common, but case management to coordinate care was more common, if the mother had been jailed than if she was in the comparison group. The proportions of infants who were low-birth-weight and preterm were significantly higher in the study group (14% and 15%, respectively) than in the comparison group (10% and 11%); similar proportions in the two groups were small for gestational age (15-17%).
Results of multivariate analysis revealed that among infants born to women who had spent time in jail, birth weight differed significantly by mother's age: Compared with babies born to 18-24-year-olds, those whose mothers were aged 30-34 weighed 162 g less at birth, and those whose mothers were in their late 30s weighed 312 g less. In contrast, infants born to women 40 or older weighed 421 g more than those born to the youngest women. No difference in birth weight was found between infants born to 18-24-year-olds and those born to 25-29-year-olds.
The odds of low birth weight were significantly elevated if a woman had been in jail during a pregnancy at age 30-34 (odds ratio, 3.0) or 35-39 (5.6), but not at age 25-29. No low-birth-weight infants were born to women 40 or older.
The same pattern emerged in an analysis of factors associated with preterm birth: The risk of preterm birth was not increased if the woman had been in jail and aged 25-29, but was elevated if she had been in her 30s (odds ratios, 2.7 and 3.6). No preterm births occurred among older women.
An infant's odds of being small for gestational age did not differ either by whether the mother had spent time in jail or, among those born to women who had been incarcerated, by mother's age.
Well-established maternal risk factors for adverse outcomes—being black, having less than a high school education, using substances and having had a preterm birth or an infant who was small for gestational age in the past—showed expected associations with birth weight and the risk of low birth weight and preterm birth. Likewise, receipt of prenatal care before the third trimester, support services and case management were associated with improved outcomes.
Analyses restricted to births to women who had been detained demonstrated that for every day a woman spent in jail while pregnant, her infant's birth weight increased by 2 g, and the odds of the infant's being low-birth-weight decreased by 2%. Infants born to women who had been incarcerated four or more times during pregnancy weighed 224 g less than those born to women who had been jailed only once; they also had significantly elevated odds of being delivered preterm (odds ratio, 3.9). The trimester during which the woman was first detained was not associated with any outcomes studied, and none of these measures was a significant factor in the risk of an infant's being small for gestational age. In these analyses, several well-established risk factors were no longer significantly associated with adverse birth outcomes. Moreover, receipt of prenatal care was not related to birth weight or the risk of low birth weight, and case management was not related to the odds of preterm birth.
The researchers had expected to find associations between incarceration during pregnancy and poor birth outcomes, owing to levels of stress experienced by women who spend time in jail. That they found no such relationship for young women, they suggest, may reflect younger women's greater resilience to stress, better general health and less severe chemical dependency. They speculate that the unexpected positive association between incarceration and birth weight for the oldest women may be explained by selection bias or by the beneficial effects for older women of services available in jail.
In conclusion, the researchers remark that "correctional facilities are important sites for public health intervention to improve birth outcomes for high-risk women." They urge public health and criminal justice officials "to develop effective, comprehensive programs," including enhanced prenatal care services and transitional resources, for incarcerated pregnant women.
1. Bell JF et al., Jail incarceration and birth outcomes, Journal of Urban Health, 2004, 81(4):630-644.