Study Examines How Pregnancy May Help the Body Eliminate Mercury from Fish

Researchers at the University of Rochester are investigating whether natural biological changes during pregnancy help reduce a fetus’s exposure to mercury. The project will examine how the maternal gut microbiome and pregnancy-related physiological changes may increase the body’s ability to eliminate methylmercury, the toxic form of mercury commonly found in fish, before it reaches the developing fetus.

“Much of environmental health research focuses on identifying risks,” said Matt Rand, PhD, associate professor of Environmental Medicine and the study’s principal investigator. “What excites us about this project is the opportunity to understand the body’s natural defenses. Namely, how pregnancy itself may help protect the fetus from environmental exposures like mercury.”

Building on decades of mercury research

Concern about prenatal mercury exposure has driven decades of research into how fish consumption affects fetal brain development. One of the most consequential efforts is the Seychelles Child Development Study, a landmark international research program that has followed families in the Seychelles for decades.

That work, led by scientists at the University of Rochester, has found no measurable harm to children’s neurodevelopment in a population that consumes roughly ten times more fish than in the United States. These and other findings have helped shift public-health guidance toward encouraging pregnant people to eat fish to obtain key nutrients important for fetal brain development.

Still, questions remain about how the body manages mercury exposure during pregnancy.

A new hypothesis: pregnancy may boost mercury elimination

Rand and his colleagues have uncovered preliminary evidence suggesting that pregnant women may eliminate mercury more efficiently later in pregnancy.

Using advanced laser ablation mass spectrometry, the team can analyze a single strand of hair to reconstruct patterns of mercury exposure and elimination throughout pregnancy. Early results suggest that mercury may be cleared from the body more rapidly during the third trimester, a key time in fetal development, than in earlier stages.

The researchers believe changes in the gut microbiome, the community of microbes that live in the digestive system, may help drive this process. Previous studies from Rand’s laboratory have shown that the microbiome plays a major role in converting methylmercury into forms that the body can more easily excrete.

If pregnancy-related shifts in the microbiome enhance this process, they could represent a natural protective mechanism that reduces fetal exposure.

Tracking mercury exposure in mothers and babies

The study, which is supported by a grant from the National Institute of Environmental Health Sciences, will recruit pregnant people who already eat fish and plan to continue doing so during pregnancy, consistent with federal dietary guidelines.

Participants will provide stool samples early and late in pregnancy so researchers can track changes in the gut microbiome. Maternal and newborn hair samples will allow scientists to reconstruct mercury exposure throughout pregnancy. The noninvasive approach could provide a unique window into how mercury is transferred between the mother and the fetus.

“Pregnant patients often receive mixed messages about fish consumption,” said Loralei Thornburg, MD, a professor of Obstetrics and Gynecology at the University of Rochester and co-investigator of the study. “This research will help us better understand how the body handles mercury during pregnancy and may ultimately guide clearer recommendations that support both maternal nutrition and fetal health.”

Beyond mercury, the researchers believe the tools developed for this project, including hair-based exposure profiling and microbiome analysis, could eventually be applied to other environmental contaminants, such as PFAS, which is thought to affect fetal and maternal health.