If you're pregnant, should you eat fish? They're full of omega 3 fatty acids, great for a baby's developing brain, but they can also contain mercury.
To chart a course through these troubled waters, America's health regulator, the Food and Drug Administration (FDA), has issued new guidelines for expectant mums.
It reckons the health benefits outweigh the risks, provided you choose the right fish. Pregnant and breastfeeding women should eat eight to 12 ounces of salmon, Pollack, squid, sardines or oysters a week. The fish have the highest levels of EPA and DHA oils and the lowest levels of mercury.
Fish to avoid include shark, swordfish, mackerel and tuna as they have the highest levels of mercury.
Taking omega 3 supplements doesn't seem to have the same beneficial effects as eating fish.
The omega 3s help the brain develop, and also maintain healthy connections in the body's neurotransmitters.
(Source: American Journal of Obstetrics and Gynecology, 2014; 211 (5): 475)