Do pregnant women need fish oil supplementation?

By Dr. James Lee
MBBS, MRCOG, FAMS, GDip

It is important that a pregnant woman should not consume any medication, herbal product or health care supplement unnecessarily or in excess, unless there is strong evidence that she needs it to improve the health of the pregnancy and/or the fetus inside her womb. The use of fish oil during pregnancy and breastfeeding remains contentious. Pregnant women are advised to understand the potential benefits and ills when they decide to take fish oil supplement.

What is fish oil?

Fishes that flourish in cold “temperate” oceans have generally higher content of oil in their muscles and organs. Fish oil comprises mainly omega-3 fatty acids, and DHA and EPA are the two most important omega-3 fatty acids. Omega-3 fatty acids are important building blocks of fatty tissues in human, such as the gray matter of the brain, the light receiving layer (retina) of the eyes and the extensive nerve network.

Why are Omega-3 fatty acids important during pregnancy & breastfeeding?

The critical window when DHA is taken up into these tissues is between the second half of pregnancy and the first two years of life. When animals were fed with diet deficient in DHA, the studies found that the vital nerve organs formed had a different fatty acid composition (with higher omega-6 fatty acids). These changes in fatty acid composition gave lasting negative effects on learning behaviour, brain metabolism, nerve formation and visual functions. These neural changes could not be reversed even when subsequent omega-3 fatty acid treatment successfully return the composition to what it should be. We cannot ignore the significance of adequate omega-3 fatty acid accretion into neural tissue during this window period. Optimizing neural tissue development is by far the most important function of omega-3 FAs in the perinatal period. Nevertheless, omega-3 FA deficiency in pregnancy has been associated with preterm labor, increased risk of postnatal depression, increased tendency of the offspring to develop asthma and other allergic conditions.

What are the natural sources of Omega-3 FA?

The basic omega-3 FA is ALA (alpha-linolenic acid), from which the functionally important omega-3 fatty acids like DHA and EPA are derived. In nature, DHA and EPA are mostly found in fatty fish such as salmon, tuna, sardines and trout. ALA, on the other hand, is a major component of some plant oil,such as canola oil and flaxseed oil. The idea of consuming ALA in large amount of plant oil, so that the body can make DHA and EPA to incorporate them into the brain, is possible, but highly inefficient. The conversion process demands a lot of chemical energy in the body and is extremely slow. Consuming pre-formed DHA and EPA is the better option.

Pregnant women are advised not to eat too much fish!

Years of industrialization have polluted the oceans, by pumping industrial chemicals and toxic wastes directly into the ocean, or by first polluting the atmosphere before poisoning the seas via the rain. Significant levels of mercury, polychlorinated biphenyls (PCBs) and dioxin have been found concentrated in oily ocean fishes. The bigger fishes that survived years of ocean living are more contaminated. These pollutants are toxic to the nerve tissues, especially while the nerves are maturing, and the growing fetus is therefore extremely vulnerable. The pregnant women are to stay away from eating large oily fish, such as shark, swordfish, marlin and king mackerel. In fact, UK and US authorities have advocated restricting their pregnant women to two fish meals a week (i.e. about 340gm a week). Fishes that are bred in the tropics are usually are less contaminated.

On the other hand, the adequate consumption of omega-3 fatty acid is essential for fetal brain growth. On weighing all sides, most authorities proselytise that the health benefits of pregnant women eating fish with low level of mercury contamination outweigh the risks of the pollutants.

Pregnant women are encouraged to eat fish with low mercury contamination, to remove the skin and fat prior to cooking. They are advised against eating raw fish or shellfish, instead, baking, broiling, steaming the fish will reduce the industrial pollutant level.

If not from fish, where else can I get enough Omega-3s?

Pregnant women who do not eat fish, who are not keen to take them while pregnant, or are eating mainly non-oily fish (tropical species), may obtain their omega-3 fatty acids by fish oil pill. The fish oil supplements should be packaged with purified fish oil, so that the PCBs and dioxin contaminants are removed. There are many formulations of fish oil supplements, their characteristics may affect their efficacy, although to date, the claims are not sufficiently researched. The consensus however is to take between 200mg and 300mg of omega-3 fatty acids a day.

What about fish liver oil?

Pregnant women ought not to consume fish liver oil, such as cod liver oil. Fish liver is the main organ where mercury is detoxified and therefore has the highest concentration of the pollutant. Besides, vitamin A (which is fat soluble) is largely stored in the liver, and thus the liver has the highest level of vitamin A in the body. Excessive vitamin A usage in pregnancy is associated with fetal malformation.

Does fish oil supplementation make better babies?

The potential effects of DHA supplementation in pregnancy on early childhood development are promising. Evidence from animal studies and observational surveys has found improved visual response, brain functioning and childhood intelligence scores. Increased DHA in baby’s blood at birth has also been correlated with reduced incidence of childhood allergic diseases such as asthma, atopic dermatitis and allergic rhinitis.

Several interventional randomized controlled trials have been organized to verify these benefits. Some of them have been going on for several years, and their interim results published. To date, the conclusions have been inconsistent; some studies showed beneficial outcomes with DHA supplementation, whereas others found no advantage. This is not unexpected as the study design and the result analysis have to consider many confounding factors that affect the baby’s development and functioning.

Unfortunately we have as yet no consistent proof that fish oil supplementation will give clinical benefits to the children as they grow older. What has been established is the safety of using fish oil supplementation in pregnancy and during breastfeeding. We look forward to more evidence of its clinical effectiveness in the coming years.