Each year there are about 4 million births in the US. About 70% of women take at least one prescription medication in pregnancy, and for many of these medications, there is inadequate safety data. Large observational studies are instrumental in closing this evidence gap because pregnant women are routinely excluded from clinical trials. Our team has had many successes in generating evidence on the safety of medications used in pregnancy including antibiotics, antihypertensive medications, and antidepressants. To study an even wider range of medications and evaluate more important but rarer outcomes, we will need to draw on larger data resources, such as WA-APCD, to identify large populations of pregnant women and their infants. The objective of this research proposal is to carry out feasibility work to investigate whether the Washington State All-Payer Database can be used to study medication use in pregnancy. Specifically, we will investigate means to identify pregnancies and to link mothers’ data to their babies. Once we can establish this data linkage, we will conduct descriptive analyses to support grant applications. For instance, we’ll count the number of mom-baby pairs contained in WA-APCD and describe their characteristics, examine frequency of use of various medication classes in pregnancy, and describe the prevalence of outcomes of interest such as birth defects. We may submit a conference abstract and a manuscript describing methods we used to link moms and babies with aggregated data as described above. Ultimately, results from future research based on the WA-APCD data could help pregnant women and their clinicians make informed decisions about medication treatment in pregnancy.