It’s a bit of a conundrum during pregnancy: Fish provides the developing fetus with essential nutrients, including omega-3 long-chain polyunsaturated fatty acids. At the same time, swimmers can introduce mercury into the diet, and mercury is a potent toxin that can cause permanent neurological damage.

Findings published in JAMA Network Open should help expectant mothers to rest a bit easier the next time they troll for dinner at the fishmonger. In a study that looked at 805 mother-and-child pairs from five European countries, pregnant women were queried about their weekly fish consumption and were also assessed for mercury exposure. When the children were 6–12 years old, they underwent a clinical examination that included measuring waist circumference, blood pressure, cholesterol numbers and insulin levels. These measures were combined to calculate what was called a metabolic syndrome score.

Children of women who ate fish from one to three times a week while pregnant had lower metabolic syndrome scores than children of women who ate fish less than once a week. It was a case of diminishing returns, however—the benefit declined if participants ate fish more than three times a week.

It’s possible that when women eat fish more frequently, contaminant exposure counterbalances the beneficial effects experienced at more moderate fish consumption levels. The study did find that higher mercury concentration in a woman’s blood was associated with a higher metabolic syndrome score in her child. Pregnant women can reduce their exposure by targeting lower-mercury species like salmon and sardines, while steering clear of riskier choices, including swordfish, orange roughy and ahi tuna.