I started taking fish oil during my second pregnancy because I read that it reduced one's risk of developing postpartum depression. It has worked like a charm in two pregnancies. Zero postpartum tears and no baby blues. In fact, I feel very happy and emotionally stable whenever I take fish oil. I have noticed that it really helps my children as well. My latest reading on fish oil here:
Taking fish oil...
prevents allergies: here
helps reduce inflammation/autoimmune disease: here
Helps autism/ADHD: here, here, here
helps pregnancy/fertility: link
We use this fish oil. It is pharmaceutical grade and tested for contamination (mercury, etc.).