Marine oil supplementation to improve pregnancy outcomes
Biological, behavioural and contextual rationale
Omega-3 fatty acids are long-chain polyunsaturated essential fatty acids that are necessary for good health and development. Unlike omega-3 fatty acids from plant sources such as flaxseed and canola oils, fish oils and algae-derived marine oils contain the longer-chain docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids. These are called essential fatty acids because the body cannot produce them independently, so they must be consumed in adequate amounts.
The prenatal period is a time of increased risk for omega-3 deficiency as maternal tissue stores tend to decline 1 as they are used for the developing fetus2, 3. Marine oil supplements are often recommended to pregnant women to fulfil their omega-3 requirements.
The use of marine oil supplements during pregnancy has been studied as a possible strategy to prevent preterm birth (or increase gestational age) and prevent eclampsia, as well as to increase birth weight along with other potential benefits such as improving fetal brain development, and reducing the risk of cerebral palsy and postpartum depression 4–7. The theories behind the studies on birth outcomes were originally developed based on the observations of high birth weight and long gestation in communities with high fish consumption 8–10.
The fatty acids DHA and EPA that are contained in marine oils are the precursors of prostaglandins, which have been shown to influence the constriction of blood vessels. Among pregnant women and non-pregnant adults, marine oils have been promoted as a treatment for hypertension, or high blood pressure 11. These same components of marine oil may also delay labour and thus potentially increase the length of pregnancy and increase birth weight by preventing the production of prostaglandins that encourage the cervix to ripen 12.
Studies that have investigated these mechanisms and their potential health benefits for mothers and children have, however, been inconsistent in their results 4, 5, 10, 13, 14. The most encouraging conclusions from a recent systematic review suggest that although there is not yet enough evidence to support the routine supplementation with marine oil during pregnancy to reduce the risk of pre-eclampsia, preterm birth or low birth weight, pregnant women could benefit from marine oil supplementation as a means to increase the length of gestation 12.
Nutritional advice for pregnant women regarding marine oil consumption may be complicated with warnings that suggest limiting overall fish consumption. Fish are an important source of omega-3 fatty acids, however many types of fish may be potentially contaminated with methyl mercury or polychlorinated biphenyls (PCBs), which can be harmful to fetal development 15, 16. These potentially harmful contaminants can accumulate more in fish meat than in fish oil. However, there may still be safety concerns if unrefined fish oil preparations are consumed, as they may contain pesticides and PCB residues 17.
Dosages of DHA and EPA from marine oils also vary in terms of the amount required to achieve any potential benefit for the mother and child. Dosages in research trials range from 133 milligrams to 3 grams per day, with most women receiving a dose of approximately 2.7 grams of both EPA and DHA per day 12. Translating this amount into food sources would require a pregnant woman to eat 300 grams of cooked salmon, which would not necessarily correspond to possible fish consumption restrictions because of contaminants for women during pregnancy. Fish oil supplements do not appear, however, to cause any serious side effects such as bleeding complications or discomfort that would influence compliance issues other than the rather minor complaint of unpleasant taste 12, 18, 19.
1 Makrides M, Gibson R.S. Long-chain polyunsaturated fatty acid requirements during pregnancy and lactation. American Journal of Clinical Nutrition, 2000, 71:307S–311S.
2 Al MD et al. Maternal essential fatty acid patterns during normal pregnancy and their relationship to the neonatal essential fatty acid status. British Journal of Nutrition, 1995, 74:55–68.
3 Otto SJ et al. Maternal and neonatal fatty acid status in phospholipids: an international comparative study. European Journal of Clinical Nutrition, 1997, 51:232–242.
4 Olafsdottir AS et al. Relationship between dietary intake of cod liver oil in early pregnancy and birthweight. British Journal of Obstetrics and Gynaecology, 2005, 112:424–429.
5 Ramakrishnan U et al. Effects of docosahexaenoic acid supplementation during pregnancy on gestational age and size at birth: randomized, double-blind, placebo-controlled trial in Mexico. Food and Nutrition Bulletin, 2010, 31:S108–S116.
6 Petridou E et al. Diet during pregnancy and the risk of cerebral palsy. British Journal of Nutrition, 1998, 79:407–412.
7 Borja-Hart NL, Marino J. Role of omega-3 fatty acids for prevention or treatment of perinatal depression. Pharmacotherapy, 2010, 30:210–216.
8 Olsen SF, Joensen HD. High liveborn birth weights in the Faroes: a comparison between birth weights in the Faroes and in Denmark. Journal of Epidemiology and Community Health, 1985, 39:27–32.
9 Olsen SF, Hansen HS. Marine fat, birthweight, and gestational age: a case report. Agents Actions, 1987, 22:373–374.
10 Olsen SF et al. Randomized controlled trial of effect of fish-oil supplementation on pregnancy duration. The Lancet, 1992, 339:1003–1007.
11 Morris MC et al. Does fish oil lower blood pressure? A meta-analysis of controlled trials. Circulation, 1993, 88:523–533.
12 Makrides M et al. Marine oil, and other prostaglandin precursor, supplementation for pregnancy uncomplicated by pre-eclampsia or intrauterine growth restriction. Cochrane Database of Systematic Reviews, 2006, Issue 3, Art. No.: CD003402.
13 Harper M et al. Omega-3 fatty acid supplementation to prevent recurrent preterm birth. Obstetrics and Gynecology, 2010, 115:234–242.
14 Williams MA et al. Omega-3 fatty acids in maternal erythrocytes and risk of preeclampsia. Epidemiology, 1995, 6:232–237.
15 Nutrition in pregnancy: Scientific Advisory Committee Opinion Paper 18. London, Royal College of Obstetricians and Gynaecologists, 2010.
16 Buck GM et al. Maternal fish consumption and infant birth size and gestation: New York State angler cohort study. Environmental Health, 2003, 2:7–16.
17 Rawn DFK et al. Persistent organic pollutants in fish oil supplements on the Canadian market: polychorinated biphenyls and organochlorine insecticides. Journal of Food Science, 2008, 74:T14–T19.
18 Makrides M. Is there a dietary requirement for DHA in pregnancy? Prostaglandins, Leukotrienes and Essential Fatty Acids, 2009, 81:171–174.
19 Akabas SR, Deckelbaum RJ. Summary of a workshop on n-3 fatty acids: current status of recommendations and future directions. American Journal of Clinical Nutrition, 2006, 83:1536S–1538S.