Purpose-To review the literature describing patterns of out-patient prescription drug use during pregnancy by therapeutic category, potential for fetal harm, and overall.Methods-We conducted a systematic review of peer-reviewed literature published from 1989 to 2010. We included studies evaluating individual-level exposures to prescription medicines during pregnancy. We selected only studies conducted in developed (OECD) countries and published in English.Results-Published drug utilization studies reveal wide variation in estimates of overall prescription drug use in pregnancy (27% to 93% of pregnant women filling at least one prescription excluding vitamins and minerals). Among studies of similar design, estimates were lowest in Northern European countries (44% to 47%) and highest in France (93%) and Germany (85%). Measured rates of use of contraindicated medicines in pregnancy ranged from 0.9% (Denmark; 1991 Conclusion-Avoidable inconsistencies in study design and reporting attenuate conclusions that can be drawn from the literature on antenatal drug utilization. Nevertheless, the body of published research shows that antenatal prescription drug use is common, with many studies finding that a majority of women use one or more prescription medicine during pregnancy. Similarly, studies consistently report the use of drugs recognized as having potential risks in pregnancy. Given this widespread use, it is particularly important to develop standards for calculating and reporting antenatal exposures to improve the value of future research in this area.

Researchers should be aware of the threat of regression to the mean when constructing matched samples for difference-in-differences. We provide guidance on when to incorporate matching in this study design.

Insurance transitions-sometimes referred to as "churn"-before and after childbirth can adversely affect the continuity and quality of care. Yet little is known about coverage patterns and changes for women giving birth in the United States. Using nationally representative survey data for the period 2005-13, we found high rates of insurance transitions before and after delivery. Half of women who were uninsured nine months before delivery had acquired Medicaid or CHIP coverage by the month of delivery, but 55 percent of women with that coverage at delivery experienced a coverage gap in the ensuing six months. Risk factors associated with insurance loss after delivery include not speaking English at home, being unmarried, having Medicaid or CHIP coverage at delivery, living in the South, and having a family income of 100-185 percent of the poverty level. To minimize the adverse effects of coverage disruptions, states should consider policies that promote the continuity of coverage for childbearing women, particularly those with pregnancy-related Medicaid eligibility.

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