Taking fish oil supplement during pregnancy has good and bad effects. Generally, there are two types of fish oil supplement – one is made from the liver of the fish and the other is from the body of the fish.  
 
Fish oil supplements made from the liver of the fish, for example cod liver oil which comprises the vitamin A1 which is not good for pregnant women. So supplement made from the liver of the fish is not recommended during pregnancy. However, fish oil supplements which are not derived from fish livers (omega-3) have lots of DHA (docosahexaenoic acid) and play a vital role in the development of your baby's eyes and brain. However, you can get plenty of DHA from wide range of foods and these natural sources of DHA have the same benefits as those from fish oil supplements.

The Food Standards Agency suggests that pregnant women having a balanced diet do not have to take fish oil supplements, in particular, cod liver oil. Some people believe that the fish oil supplements will enhance your baby's cognitive development. And there are some studies which indicate that having fish oil supplements during pregnancy can help to prevent low birth weight and premature birth.