A growing number of studies suggest that pregnant women who eat at least three servings of fish per week can positively impact their child’s overall brain function, but at what cost? A recent study published in the JAMA Pediatrics has found that women who eat the recommended three servings of fish a week during pregnancy increase thier child's risk for obesity.

"Women who ate fish more than three times per week when they were pregnant gave birth to children with higher BMI values at two, four and six years of age compared with women who ate fish less," the study concluded. "High maternal fish intake during pregnancy also was associated with an increased risk of rapid growth from birth to two years and with an increased risk of overweight/obesity for children at ages four and six years compared with maternal fish intake while pregnant of once a week or less."

A research team led by Dr. Leda Chatzi, from the University of Crete, gathered data from 26,184 pregnant women and their children every two years until each child turned 6. All pregnancies ended in single deliveries and occurred between 1996 and 2011 in Europe and North America. Expecting mothers were asked to gauge how much fish they consumed on a weekly basis and children had their BMI recorded during each follow up.

Fish consumption varied by which country pregnant women were from. For example, women from Belgium consumed a relatively small amount of fish at 0.5 times per week while women from Spain ate fish 4.45 times per week. Women from Massachusetts consumed, on average, one to two servings of fish per week. Both the FDA and EPA recommended that pregnant women eat two to three servings of fish per week back in July 2014.

Children born to mothers who reported the highest level of fish consumption during pregnancy were between 14 percent and 22 percent more likely to be overweight or obese by the ages of 4 and 6 compared to children born from mothers with the lowest amount of fish consumption. 

Fears over mercury contamination have caused a lot of pregnant women to become wary of fish, however, some doctors say pregnant woman shouldn't neglect the omega-3 fatty acids found in fish, which are essential to fetal development. Fatty fish sources of omega-3 fatty acids include salmon, mackerel, herring, sardines, and tuna.

Chatzu and her colleagues from this new study speculated these fatty acids could also lead to fetal stem cells developing into fat cells. Another explanation they deemed “speculative” was that the pollutants found in fish, including mercury, could disrupt fetal hormones that result in more fat storage and are associated with metabolism.

Source: Stratakis N, Roumeliotaki T, Chatzi L, et al. Fish Intake in Pregnancy and Child GrowthA Pooled Analysis of 15 European and US Birth Cohorts. JAMA Pediatrics. 2016.