The CDC recommends the use of DEET to protect people against the mosquito that carries the Zika virus, especially pregnant women. But there are very few published studies looking at the possible effects of DEET on unborn children, and none of the existing studies looked at exposure during the first trimester. One study conducted in Thailand found that daily usage of 20% DEET did not affect the fetus development or growth, but the study only looked at second and third trimester exposures. The study also found that DEET can cross the placenta and reach the fetus, but out of 900 participants only 50 were found to have DEET in the umbilical cord.

Still, given the lack of research—especially for first trimester exposures, when most birth defects develop—there is reason to be cautious. The PROTECT Center’s Project 1, led by Dr. John Meeker, is tracking concentrations of DEET and other pesticides in subset of the PROTECT cohort of pregnant women to see whether these pesticides are linked to adverse pregnancy outcomes. Dr. Meeker’s research includes first, second, and third trimesters, and will continue to follow children from birth through age four as part of the new CRECE Center.

Click here to read more about the CDC’s recommendations.