Fish Oil During Pregnancy

Pregnant woman on the beach

The relationship between expectant mothers and Omega-3 fatty acid, a major component of fish oil, first caught the interest of Danish investigators in 1980s. It was observed that women on the Faroe Islands had gestation periods that lasted four days longer and they gave birth to babies that weighed 194 grams more than the average birth weight of babies born in Denmark.1 Researchers found that Danish expectant mothers had lower Omega-3 to 6 ratio than the Faroese mothers to be, and if Danish women adjusted their diet to increase this these fatty acids in their blood, then their gestation would possibly increase by nearly six days.

A Norwegian study compared the mental processing scores of children whose mothers took cod liver oil supplements during pregnancy to those whose mother’s diets were supplemented with corn oil (rich in Omega-6s). It was concluded that children whose mother’s used cod liver oil (rich in Omega-3s) had better mental processing results.2 An Australian group of researchers carried out a similar trial and also came to the same conclusion, that mothers whose diets were supplemented with fish oil produced offspring with higher mental processing scores.3

DHA is one of the two types of Omega-3s. In a study using Inuit women of Arctic Quebec, it was found that the elevated DHA concentrations in the mothers’ blood also resulted in proportionally higher baby’s cord blood concentrations. These elevated DHA concentrations led to enhanced visual awareness as well as mental and psychomotor skills in the baby.4

So how is a mother to be supposed to meet her omega-3 requirement? The best option is to have two servings of omega-3 rich fish a week. Many expectant mothers avoid seafood for fear of mercury contamination, even though the risk is negligible at best. However, if they did consume seafood twice a week, it would only provide 100 to 250 milligrams of omega-3s a day, whereas the goal during pregnancy should be 650 mg, with 300 mg being DHA.5 To make up the shortfall, fish oil supplements may be recommended by the doctor.

Fish oil supplements, generally tend to house 1 to 2 parts per billion (ppb) of mercury, which is significantly more than what is typically found in seafood (0.05 ppb). However, the quantity of fish oil in supplements is much less than the quantity consumed when seafood is eaten (200 g, two times a week). Thus, toxicity from mercury becomes insignificant in fish oil supplements also. While cod liver oil is considered to be another good source of EPA and DHA, it is important to note that it is also a good source of vitamin A and prolonged excessive use of vitamin A, enhances the risk of osteoporosis.


  1. Olsen SF, Hansen HS, Sorensen TI, et al. Intake of marine fat, rich in (n-3)-polyunsaturated fatty acids, may increase birthweight by prolonging gestation. Lancet. 1986;2:367¬369.
  2. Helland IB, Smith L, Saarem K, et al. Maternal supplementation with very-long-chain n-3 fatty acids during pregnancy and lactation augments children’s IQ at 4 years of age. Pediatrics. 2003;111:e39¬e44.
  3. Dunstan JA, Simmer K, Dixon G, et al. Cognitive assessment of children at age 2(1/2) years after maternal fish oil supplementation in pregnancy: a randomised controlled trial. Arch Dis Child Fetal Neonatal Ed. 2008;93:F45¬F50.
  4. Jacobson JL, Jacobson SW, Muckle G, et al. Beneficial effects of a polyunsaturated fatty acid on infant development: evidence from the Inuit of Arctic Quebec. J Pediatr. 2008;152:356¬364.
  5. Simopoulos ATP, Leaf A, Salem N. Essentiality of and recommended dietary intakes for omega-6 and omega-3 fatty acids. Ann Nutr Metab. 1999;43:127¬130.
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By Andy

Hi, my name is Dr. Andy Williams and I am a biologist with a keen interest in diet and nutrition. This site was set up to help me explore the research, facts and fiction about Krill Oil. Please feel free to contact me if you have any comments, questions or suggestions.

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