


Posted on by 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.

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 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.

Posted on by Carissa M. Rocheleau, PhD

8 comments on “Can Workplace Exposures Increase Risks of Birth Defects? – Epidemiology in Action”


    Workplace safety is about preventing injury and illness to employees. To make the workplace safer, the organization has to acknowledge which potential health and safety hazards are present. Or determine where and what and how a worker is likely to become injured or ill. It starts with analyzing individual workstations and program areas for hazards — the potential for harm — be it a frayed electrical cord, repetitive motion, toxic chemicals, mold, lead paint or lifting heavy objects.

    Is there any evidence that workplace exposure to ozone emanating from office machinery is a reproductive hazard?

    Note: This comment was edited to ensure privacy.

    This is a reasonable question to ask, because laser printers can produce small amounts of ozone. In high concentrations, there is evidence from animal studies that ozone can cause adverse effects on a fetus. Although high-quality human studies have not yet answered this question for sure, based on the current evidence I think it is unlikely that ozone from office machinery is a reproductive hazard.

    Most office equipment does not produce ozone—only some laser printers. Inkjet printers do not produce ozone. In closed-chamber testing, most laser printers have only produced very small amounts of ozone for a short period of time during printing. The NIOSH Recommended Exposure Limit (REL) for ozone is 0.1 parts per million (ppm) as a ceiling. Although we do not know for sure what level of ozone exposure is safe for a fetus, previous animal studies only showed effects on offspring at considerably higher concentrations than 0.1 ppm, often for 24 hours a day for all or most of the pregnancy. At the concentrations where reproductive effects were seen, the pregnant animal also had pronounced respiratory symptoms. So for these reasons, in a typical office I expect ozone concentrations to be well below levels at which any fetal effects were observed in animal studies.

    More information on NIOSH’s recommendations regarding ozone can be found at

    Can you send me the reference to the original article on Hypoplastic Left Heart Syndrome and exposure to herbicides and insectides? I will greatly appreciate .

    That article is currently in press. We will post a link as soon as it is available online.

    I think that it is important to understand how birth defects happen. There is a lot to look into for pregnant women. I hope women that are pregnant look into why birth defects happen and how to prevent it.

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