Who seeks Teratology Information Service's advice? Assessing the risk of selection bias in observational cohort studies on drug risks in pregnancy.

All women of reproductive age should have access to Teratology Information Services (TIS). Observational cohort studies based on TIS data are one of the most important sources for risk characterization of drugs during pregnancy. A selection in TIS populations towards higher socioeconomic level would compromise the TIS' goal of health prevention and the quality of research. The aim of this study is to investigate in which respect Berlin TIS enquirers are different from the general female population of reproductive age in Germany. 5,239 women aged between 20 and 39 were compared with the general female population of reproductive age in Germany. Medium- and high-level educated women tend to be overrepresented among TIS enquirers. TIS should strive towards reaching subpopulations with poor access to health care. TIS-based observational studies require appropriate comparison cohorts from the same data pool with similar procedures of ascertainment to reduce the risk of selection bias.