Fish contain something essential to human health and development: omega-3 fatty acids. They contribute to, among other things, brain and heart health, and they're especially important to the developing brain and heart of a fetus. The human body cannot make omega-3s. People have to get them from outside sources, and one of the richest sources is fatty fish.
Coldwater seafood such as salmon, lake trout and sardines are excellent sources of omega-3s, including one of the most important ones for a growing fetus (and baby, for that matter), called DHA. Fish oil supplements containing DHA are a possibility during pregnancy, but they do have side effects for some people, like excessive burping or nausea, which pregnant women already may have trouble with.
Some nonfish sources of omega-3s include walnuts, eggs and flaxseed. They don't have nearly as much as fish, though. Two 4-ounce servings of low-mercury, coldwater fish per week should take care of the omega-3 requirement [source: AskDrSears].
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