NIOSHBy Carissa M. Rocheleau, PhD

Pregnant and breastfeeding women get a lot of advice from just about everyone on just about everything– what to eat, medications to avoid, how much exercise they should do. When it comes to their jobs, though, the advice seems to dry up. That’s because occupational exposure limits are based on studies of healthy, non-pregnant workers and many early studies of occupational hazards were limited to men. These recommended exposure limits might not be sufficient to protect a developing fetus. We are trying to find out whether things people were exposed to at work like chemicals, noise, shift work, radiation, or germs affect their pregnancy outcomes and health of their children. One of the outcomes we study is birth defects.

Epidemiology is the art and science of using data to answer questions about the health of groups. In occupational epidemiology, we use that data to understand how work affects health. This blog entry is part of a series that shares the stories behind the data.

Birth defects affect 1 in 33 births in the United States. They are a leading cause of infant death, and can result in disabilities lasting a lifetime. One of the big challenges in studying birth defects is that there are really 3 people involved: mom, dad, and the baby. A chemical could damage either parent’s reproductive system before conception, which might cause harm to the fetus; a chemical could change the mother’s body in a way that harms the fetus, such as reducing the amount of certain nutrients in her blood; or a chemical could pass through the placenta and directly affect the fetus. Also, anyone who lives in the household could bring hazardous chemicals home on their skin, shoes, and clothes.

How are we studying birth defects and occupation?

In order to untangle all these possible routes of exposure, we need to compare a lot of families. Although birth defects are not uncommon, specific types of defects are much rarer; that means we need to study thousands of pregnancies. We worked with the National Birth Defects Prevention Study (, one of the largest studies of birth defects in the United States. This study is coordinated by CDC’s National Center for Birth Defects and Developmental Disabilities together with birth defects registries from ten states. Mothers of infants with and without birth defects were asked many questions about their health, lifestyle, diet, and...Click here to read the rest of the post.