Parental incarceration is associated with mental and physical health problems in children, yet little research directly tests mechanisms through which parental incarceration could imperil child health. We hypothesized that the incarceration of a woman or her romantic partner in the year before birth constituted an additional hardship for already-disadvantaged women, and that these additionally vulnerable women were less likely to engage in positive perinatal health behaviors important to infant and early childhood development. We analyzed 2006-2010 data from the Pregnancy Risk Assessment and Monitoring System to assess the association between incarceration in the year prior to the birth of a child and perinatal maternal hardships and behaviors. Women reporting incarceration of themselves or their partners in the year before birth of a child had .86 the odds (95 % CI .78-.95) of beginning prenatal care in the first trimester compared to women not reporting incarceration. They were nearly twice as likely to report partner abuse and were significantly more likely to rely on WIC and/or Medicaid for assistance during pregnancy. These associations persist after controlling for socioeconomic measures and other stressors, including homelessness and job loss. Incarceration of a woman or her partner in the year before birth is associated with higher odds of maternal hardship and poorer perinatal health behaviors. The unprecedented scale of incarceration in the US simultaneously presents an underutilized public health opportunity and constitutes a social determinant of health that may contribute to disparities in early childhood development.