Fathers' occupational exposures may play an important role in the development of birth defects

Can exposure to hazardous substances at work contribute to the development of birth defects? If so, then fathers' occupational exposures may play a more important role than mothers' exposures, suggests a study in the September Journal of Occupational and Environmental Medicine, official publication of the American College of Occupational and Environmental Medicine (ACOEM).

Led by Dr. Sin-Eng Chia of National University of Singapore, the researchers looked at whether rates of common birth defects were related to parents' occupations. The study included data on all babies born in Singapore from 1994 through 1998—nearly 238,000 infants.

Links between occupational categories and birth defects were much more common for the fathers' jobs than for the mothers'. For example, babies whose fathers were clerical workers were 2.25 times more likely to be born with heart defects, compared to those who worked as senior officers and managers.

The risk of heart defects was also approximately doubled for babies of fathers classified as production craftsmen. The same job category was also linked to a nearly tripled risk of a group of relatively minor congenital musculoskeletal deformities.

One fathers' job category—plant and machine operators and assemblers—was linked to all three of the most common birth defect categories. Associations included a 2.5 times increase in heart defects, a tripled risk of musculoskeletal defects, and more than a fivefold increase in risk of defects involving the urinary system.

For mothers' occupations, just one significant relationship was found. The risk of urinary system defects was about 3.5 times higher for babies whose mothers were classified as professionals.

In Singapore as in other developing countries, more and more women are working outside the home, including during pregnancy. This makes it important to understand how possible exposure to hazardous conditions at work might affect the risk of birth defects.

However, the new results suggest that fathers' exposures are more strongly related to birth defects than the mothers' exposures are. The risks may be highest for fathers working as plant and machine operators, compared with those working at the senior or managerial level.

More research is needed to clarify the true meaning of the results. For example, the links between occupational groups and birth defects may reflect social and economic factors, rather than exposure to hazardous substances.

The study finds no specific exposures linked to specific birth defects, but it does highlight the potential importance of fathers' occupational exposures. "Future studies of pregnancy outcomes should not ignore the father," Dr. Chia and colleagues conclude.

ACOEM, an international society of 6,000 occupational physicians and other healthcare professionals, provides leadership to promote optimal health and safety of workers, workplaces, and environments.