Cheap, convenient, and full of protein canned tuna is a classic staple in kitchen cabinets across the country, but a new study by Consumer Reports warns it may be “too risky” to eat during pregnancy. The study looked for mercury in samples of canned tuna packed in water from five popular brands. Consumer Reports says it found six individual spikes in mercury content that researchers deemed troublesome.

“Mercury levels can spike in unpredictable ways that might jeopardize the health of a fetus,” says James Rogers, Director of Food Safety Research and Testing at Consumer Reports. “The variation we see from can to can make tuna too risky for pregnant people”. The organization’s advice is to avoid canned tuna altogether if you are pregnant. It also recommends children should eat light or skipjack tuna only.

According to the current guidelines from the American College of Obstetricians and Gynecologists pregnant women can safely consume up to six ounces of tuna per week.