Maternal occupation and the risk of birth defects: an overview from the National Birth Defects Prevention Study.

OBJECTIVES: To examine the association between a spectrum of 24 maternal occupations and 45 birth defects for hypothesis generating purposes.
METHODS: Cases of isolated and multiple birth defects (n = 8977) and all non-malformed live-born control births (n = 3833) included in the National Birth Defects Prevention Study (NBDPS) with estimated dates of delivery from 1 October 1997 through 31 December 2003 were included. A computer-assisted telephone interview with mothers was conducted. Occupational coding using the 2000 Standard Occupational Classification System and the 1997 North American Industry Classification System was completed for all jobs held by mothers. Jobs held from 1 month before pregnancy to the end of the third pregnancy month were considered exposures. Logistic regression models were run, adjusted for potential confounders. We also used a Bayesian approach to logistic regression.
RESULTS: Approximately 72% of case mothers and 72% of control mothers in the NBDPS were employed. Several occupational groups were positively associated with one or more birth defects, including janitors/cleaners, scientists and electronic equipment operators. Using standard logistic regression, we found 42 (26 for Bayesian) significantly elevated risks of birth defects in offspring of working mothers. In addition, several other occupational groups were found to be negatively associated with one or more birth defects, including teachers and healthcare workers. Using standard logistic regression, we found 12 (11 for Bayesian) significantly reduced risks of birth defects among offspring of working women.
CONCLUSIONS: Results from these analyses can be used for hypothesis generating purposes and guiding future investigations of occupational exposures and birth defects.