fish oil supplements during pregnancy

Researchers found that fish oil supplements during pregnancy were associated with prolonged pregnancy duration and increased birth weight.

The process of creating a human being in a woman’s uterus is a highly complex and sophisticated process. There are many factors that need to be taken into consideration for a healthy pregnancy, one such factor being a woman’s dietary habits during pregnancy. Poor nutrition affects not only the course of the pregnancy and how the fetus develops, but it can also affect the life of the child after birth. Insufficient nutrients can lead to problems with normal patterns of growth in the uterus and it can also reduce the amount of time that the baby is able to remain in the uterus. Both factors can increase the likelihood of being diseased as well as potentially impair development.

The term ‘fish oil supplements’ is one that is sure to have been heard a few times in discussions of health and wellness, with the general theme around the topic seeming to be that fish oil is something that is good for you. But what is fish oil, and does it actually have any health benefits? Is it something that pregnant women should add to their diet?

Fish oil is derived from the tissues of oily fish and, in general, it is the omega-3 fatty acids in fish that have been associated with beneficial outcomes. Previous research on fish intake and pregnancy has shown that there are positive effects on pregnancy outcomes that are associated with high fish intake. This effect of high fish intake has been connected to a class of molecules, known as ‘n-3 long-chain polyunsaturated fatty acids (LCPUFAs)’, that are present in the fish. Prior research into the effect of n-3 LCPUFA supplements during pregnancy has shown that this supplementation increases the duration of pregnancy, and as a result, also increases the birth weight of the baby.

A group of researchers conducted a study on the relationship between supplementation with n-3 LCPUFAs, through the use of fish oil supplements, and duration of pregnancy, birth weight, and size for gestational age. The study, reported in The Journal of Nutrition, consisted of 736 pregnant women who were enrolled in the study between November 2008 and November 2010. The women were recruited for the study when they were 24 weeks pregnant and remained as part of the study until one week after they gave birth. As part of the study, they were randomly assigned to either take fish oil supplements daily during pregnancy or taking olive oil pills daily. The gestational age, how far along the pregnancy a woman was, was calculated based on the woman’s expected due date. Following birth, the infant’s birth weight was measured, and fetal growth curves were used to compare the actual birth weight of the child to the expected weight based on gestational age.

Infants delivered from mothers who were taking fish oil supplements during pregnancy had a higher birth weight in comparison to infants delivered from mothers who did not. In addition, infants born to mothers from taking fish oil were larger for gestational age. In the fish oil group, there was also a two-day increase in the duration of pregnancy compared to the olive oil group.

This research is important because it is one of the largest studies regarding the use of n-3 LCPUFA supplements during pregnancy and its effects on pregnancy duration and fetal growth. The findings are consistent with most previous research, but this study also introduces new data regarding the increase in birth weight, which was not just due to an increased period of pregnancy, but a result of increased growth in the uterus (as evidenced by larger sizes for gestational age seen in the fish oil group).

There is a concern that increased pregnancy duration and birth weight could lead to “unwanted complications during pregnancy and birth”, which the researchers did not find in their study, but they acknowledge that larger studies would be needed to confirm the findings. However, in this study the researchers found that supplementation with n-3 LCPUFAs had positive effects on three different organ systems in children, indicating that n-3 LCPUFAs could have beneficial impacts on development, which should be studied further.

Fish oil supplementation appears to be a promising supplement, but future research should focus on the quantity and quality of n-3 LCPUFAs in fish oil supplements, as well as if regular supplementation during pregnancy is truly beneficial and relevant to the health of the mother and child.


Written by Haritha Thevar, BSc



Gestational age: MedlinePlus Medical Encyclopedia. (2019). Retrieved 2 November 2019, from

Villines, Z. (2019). Fish oil side effects: How much is too much?. Retrieved 2 November 2019, from

Vinding, R., Stokholm, J., Sevelsted, A., Chawes, B., Bønnelykke, K., & Barman, M. et al. (2018). Fish Oil Supplementation in Pregnancy Increases Gestational Age, Size for Gestational Age, and Birth Weight in Infants: A Randomized Controlled Trial. The Journal Of Nutrition, 149(4), 628-634. doi: 10.1093/jn/nxy204

Image by Steve Buissinne from Pixabay

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