Birth defects and neonatal morbidity caused by teratogen exposure after the embryonic period

Pharmaceutical pregnancy exposure registries seek to evaluate temporal associations between drug exposures and adverse outcomes, particularly congenital anomalies. These registries record observed associations that may or may not be causally-related to the exposure. Most major congenital malformations (i.e., structural birth defects) result from abnormal development during embryogenesis. A standardized catalog of defects of concern (colloquially the "BPA Codes") is used both in public health surveillance programs and pregnancy exposure registries. There are, however, some anomalies that cause significant morbidity and mortality for which isolated second or third trimester exposures may be pathogenically significant. There currently exists no standardized list of defects for which exposure limited to the fetal period may be problematic.

The six-digit-code list was used to determine anomalies that might result from medication exposures limited to the fetal period.

Defects with documented first trimester pathogenesis (e.g., anencephaly, heterotaxy) were eliminated from consideration, as were chromosomal and single gene disorders (e.g., trisomy 21, achondroplasia). The remaining defects include the following: (1) those that are known to or could reasonably originate or manifest after the embryonic period (e.g., porencephaly, cataracts); (2) those for which pathogenesis is unclear or variable enough that exposure at any gestational age might be considered relevant (e.g., club foot, microcephaly); and (3) those that include some component of abnormal growth (e.g., hemihyperplasia). "Unspecified" defects (e.g., "abnormality of the leg") were included by default because there is insufficient information to assume first trimester embryogenesis.

The final result is a list of major and minor anomalies in 11 organ system categories that may be caused by teratogen exposure during the fetal period. Birth Defects Research (Part A) 106:935-939, 2016. © 2016 Wiley Periodicals, Inc.