Eating omega-3 fatty acids during pregnancy may increase fetal growth, without prolonging pregnancy. Women who ate the most omega-3 seemed to boost the birth weight of the baby. Further, restricted growth of the fetus, which occurs in about one in 10 pregnancies typically, increased to one in eight among women who did not eat omega-3. If you click on the link below you'll see that the study actually recommends eating fish to get the omega-3. This is something I strongly advise against, as mercury in fish can severely harm the developing fetus--even public health officials have warned women of the dangers of eating fish during pregnancy. Instead, you should take fish oil, which is purified and does not pose the risk of introducing toxins to your baby that eating fish does, yet will give you all of the beneficial effects of omega-3.
Yahoo! News May 12, 2004