Derived mostly from plants, Omega-3 PUFAs have alpha-linolenic acid (ALA). Fish oils are comprised of eicosapentenoic acid (EPA) and docosahexaenoic acid (DHA). The omega-6 PUFAs come mainly from whole grains, vegetables, eggs and cereals and contain linoleic acid (LA) and arachidonic acid (AA).
During the 3rd trimester your baby's brain growth is at its peak. This is when these supplements were supposed to have had an effect. What seems to be more important is the ratio of the omega-3 and omega-6 fatty acids. For example, if you increase the omega-3 PUFAs, you may decrease the arachidonic acid (AA), an omega-6 PUFA, which may slow infant growth and development. DHA alone, without AA may also have negative side effects. Though it appears that real fish is what makes the difference and not artificial DHA.
This does not mean that the omega-3 PUFAs don't have a chance. In fact some recent observational studies have shown that there may be a correlation in preterm birth, precclampsia as well as hypertension in pregnancy with the Omega-3 PUFAs. Women with a history of preterm labor had a 50% reduction in preterm labor rates with omega-3 PUFAs, though the general population did not seem to benefit. Though more quality studies are needed for all of these cases.
So before you buy supplements for yourself during pregnancy or feed supplements to your baby after birth, be sure to talk to your doctor or midwife about the potential benefits for you and your baby and how they may or may not outweigh the risks. Remember, it's about a good ratio and timing. Because when all is said and done, no expert has the answer as to the appropriate amount or type of supplement that works well in pregnancy.
Carlson SE, Cooke RJ, Werkman SH, Tolley EA. First year growth of preterm infants fed standard compared to marine oil n-3 supplemented formula. Lipids 1992;27:9017.
De Groot RH, Hornstra G, van Houwelingen AC, Roumen F. Effect of alpha-linolenic acid supplementation during pregnancy on maternal and neonatal polyunsaturated fatty acid status and pregnancy outcome. Am J Clin Nutr 2004;79:251-60.
Dubnov G, Berry EM. Polyunsaturated fatty acids, insulin resistance, and atherosclerosis: is inflammation the connecting link? Metabol Synd Relat Disord 2004;2:124-8.
Dubnov G, Berry EM. Omega 6/omega 3 fatty acid ratio: the Israeli paradox. World Rev Nutr Diet 2003;92:81-91.
Larque E, Demmelmair H, Koletzko B. Perinatal supply and metabolism of long-chain polyunsaturated fatty acids. Importance for the early development of the nervous system. Ann NY Acad Sci 2002;967:299-310.
Makrides M, Gibson RA. Long-chain polyunsaturated fatty acid requirements during pregnancy and lactation. Am J Clin Nutr 2000;71(1 Suppl):307S-11S. Makrides M, et al "Effect of DHA supplementation during pregnancy on maternal depression and neurodevelopment of young children: A randomized controlled trial" JAMA 2010; 304: 1675-1683.
McCann JC, Ames B. Is docosahexaenoic acid, an n-3 long-chain polyunsaturated fatty acid, required for development of normal brain function? An overview of evidence from cognitive and behavioural tests in humans and animals. Am J Clin Nutr 2005;82:28195.
Onwude JL, Lilford RJ, Hjartardottir H, Staines A, Tuffnell D. A randomised double blind placebo controlled trial of fish oil in high risk pregnancy. Br J Obstet Gynaecol 1995;102:95100.
Olafsdottir AS, Skuladottir GV, Thorsdottir I, Hauksson A, Thorgeirsdottir H, Steingrimsdottir L. Relationship between high consumption of marine fatty acids in early pregnancy and hypertensive disorders in pregnancy. Br J Obstet Gynaecol 2006;113:301-9.
Olsen SF, Secher NJ, Tabor A, Weber T, Walker JJ, Gluud C. Randomised clinical trials of fish oil supplementation in high risk pregnancies. Fish Oil Trials in Pregnancy (FOTIP) Team. Br J Obstet Gynaecol 2000;107:38295.
Ryan AS, Montalto MB, Groh-Wargo S, Mimouni F, Sentipal-Walerius J, Doyle J, et al. Effect of DHA-containing formula on growth of preterm infants to 59 weeks postmenstrual age. Am J Hum Biol 1999;11:45767.
Smuts CM, Huang M, Mundy D, Plasse T, Major S, Carlson SE. A randomized trial of docosahexaenoic acid supplementation during the third trimester of pregnancy. Obstet Gynecol 2003;101:469-79.
Van Houwelingen AC, Sorensen JD, Hornstra G, Simonis MM, Boris J, Olsen SF, et al. Essential fatty acid status in neonates after fish-oil supplementation during late pregnancy. Br J Nutr 1995;74:72331.