Teratology Information Services (TIS) located throughout the world have long played a key role in screening for potential new human teratogens. Using a basic prospective cohort study design, TIS recruit pregnant women from among callers to the Services who have had an exposure of interest and at the same time identify an unexposed comparison group from the same pool of callers. Women in both groups are followed to pregnancy outcome and a range of adverse outcomes including major congenital anomalies, birth size, pregnancy loss, and preterm delivery are evaluated, while controlling for potential confounding. Particularly for rare exposures or newly marketed medications, TIS may be uniquely suited to gathering this information in a timely and efficient fashion. The primary limitation of these studies is the unknown representativeness of the volunteer sample, and the typical small to moderate sample sizes. Methods to increase the proportion of exposed pregnancies that are recruited should be developed. However, small sample size TIS studies, especially when considering new or rare exposures, often fulfill the important function of providing some reassurance to women who have already had the exposure of interest by ruling out major risks for teratogenicity, that is, on the order of thalidomide. Collaborations across TIS nationally and internationally help to address the sample size challenges. A formal collaboration between the TIS cohort study model with a case-control study design is also underway and will provide complementary strengths.
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