Can Workplace Exposures Increase Risks of Birth Defects? – Epidemiology in Action

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.

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 (www.nbdps.org), 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 family history of diseases. They also told us what they did at their jobs before and during pregnancy.

We worked with expert industrial hygienists to estimate exposure to chemicals based on the moms’ detailed job descriptions. This kind of exposure assessment is very time-consuming, but it is the most accurate way to estimate exposures when we don’t have direct measurements from a workplace. Most of the time, people don’t know or remember all the chemicals they are exposed to–or they can’t estimate how much of a chemical they might be exposed to, because they don’t know enough about the ventilation or other engineering controls in their workplaces.

Using the experts’ estimates of exposure intensity and frequency, we can put the moms into groups that have lower and higher exposure during the most important time periods for a developing fetus. We can then compare mothers of babies with and without birth defects to see if they differ in how much, or how often, or when they were exposed to hazardous chemicals.

Our recent research on occupational exposures and birth defects

With our collaborators from the National Birth Defects Prevention Study, we’ve studied whether pesticides, polycyclic aromatic hydrocarbons (PAHs, chemicals made when carbon-based substances burn), and certain chlorinated solvents are associated with several different birth defects. Recently, we found that exposures to fungicides, insecticides, and herbicides were not linked to most congenital heart defects, but a few rare heart birth defects were linked to specific patterns of pesticide exposure. For example, mothers of children with a condition called Hypoplastic Left Heart Syndrome (HLHS) were 5 times as likely to be exposed to high doses of both insecticides and herbicides compared to mothers of children without birth defects. There weren’t very many children with HLHS to compare, though, so other factors that differed between exposed and unexposed women may have contributed to HLHS (like differences in family history of heart defects or mom’s age). Also, we don’t know yet which specific insecticides and herbicides are linked to HLHS. These are things we are continuing to investigate.

As we learn more about how workplace exposures affect pregnancy, we share this information with other researchers by publishing scientific papers in peer-reviewed journals. We also share this information with the public on the Reproductive Health and the Workplace Topic Page.

We would like to hear from you, too. What kind of information or resources on workplace safety during pregnancy would be helpful to you as an employee, employer, health and safety officer, or healthcare provider?

Carissa M. Rocheleau, PhD

Dr. Rocheleau is an epidemiologist in the NIOSH Division of Surveillance, Hazard Evaluations and Field Studies.