The exact effects of fish oil on pregnant or breastfeeding women is unknown. However, fish oil may contain chemicals that can have been known to harm pregnant women and children. If improperly processed or manufactured, fish oil may contain heavy metals such as methylmercury, dioxins, and polychlorinated biphenyls (PCBs). These chemicals are typically found in the meat of fish, and fish oil is unlikely to carry traces of them. However, it is important for pregnant women to make sure their supplements are carefully manufactured. Because large doses of fish oil have been associated with excessive bleeding, pregnant women are recommended to take small doses of fish oil if they choose to take it.
It is not known whether the omega-3 fatty acids contained in fish oil can be transmitted to an infant through the breast milk of a nursing mother. Some studies maintain that ingesting omgea-3 fatty acids (especially docosahexaenoic acid/DHA) during pregnancy increases the birth weight and length of the infant. Because of this, small amounts of omega-3 fatty acids have been fed to some infants. If you are pregnant or wish to become pregnant, ask your doctor about the safety of fish oil supplementation.