Studies reveal that a pregnant woman’s high intake of essential fatty acids, particularly docosahexaenoic acid or DHA from her diet yields a higher cognitive function and longer attention span of their babies.
One landmark research in 2007 by Hibblen JR et al, entitled "Maternal seafood consumption in pregnancy and neurodevelopmental outcomes in childhood", showed that babies born to moms with higher blood levels of DHA had longer attention spans (an effect that lasted until their second year). Attention span is a non-verbal indicator of intelligence in infants.
Pregnant women especially need DHA during their third trimester. Most of the DHA that the fetus needs is transferred via the placenta from mother to fetus to further fuel its brain and nervous tissue development.
DHA is not naturally produced by the human body, thus, is needed to be sourced from the diet. Experts recommend that pregnant women get 300 milligrams of DHA a day (based on the International Society for the Study of Fatty Acids and Lipids Adequate Intake for DHA.) It is abundant in oily fishes like salmon, sardines, tuna, seaweed and dark green, leafy vegetables. However, it is difficult to get an adequate amount of DHA from food alone unless you are able to eat large amounts of fish (but then mercury content will be a concern.) Thus, supplementation is highly recommended. It is good to note that there are prenatal milk supplements that are fortified with good amounts of DHA.