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International Health

August 3, 2018

Pregnant women with low levels of Omega 3 fatty acids 10 times more likely to give birth prematurely, new study finds

For three decades, researchers have observed a link between consuming more fish or fish oils and longer pregnancies. The extent of the protection from preterm birth, however, has not been well defined. Results from a new study, published in EBioMedicine on August 3, show a strong and significant association between low levels of omega-3 fatty acids—found in fish oils—and early preterm birth. Women with the lowest levels in their first and second trimesters were at 10 times increased risk of early preterm birth when compared with pregnant women with the highest levels.


“We had pre-planned and registered all of our analyses prior to getting the results back from the lab, and when we saw the findings we were very excited to see such a strong association,” said Andrew Thorne-Lyman, ScD, MHS '97, co-author of the study and an associate scientist in International Health at the Johns Hopkins Bloomberg School of Public Health. “This is some of the strongest evidence yet that omega-3 fatty acids can offer protection from early preterm birth, defined as birth before the 34th week of pregnancy, which can have immense health, economic and emotional costs.”

The study was based at the Statens Serum Institut in Copenhagen and used blood samples collected in the Danish National Birth Cohort study. Researchers analyzed blood samples from 376 women who gave birth very prematurely (prior to 34 weeks of gestation) between 1996 and 2003 and 348 women who did not. Specifically, they analyzed the women’s levels of long-chain omega 3s, eicosapentaenoic acid and docosahexaenoic acid (EPA-DHA) in the first and second trimesters. 

Women in the lowest quintile of EPA+DHA serum levels—with EPA+DHA levels of 1.6% or less of total plasma fatty acids—had a 10 times higher risk of early preterm birth when compared with women in the three highest quintiles, whose EPA+DHA levels were 1.8% or higher. Women in the second lowest quintile had a 2.7 times higher risk compared with women in the three highest quintiles.

Researchers also found that the risk of preterm birth stopped declining around the 2.0-2.5% mark, suggesting there is a threshold level after which increased fatty acid levels offer no additional protection. This could play an important role in determining ideal levels of fish consumption or fish oil supplements during pregnancy.

“While causes of preterm birth are likely to vary by country and setting, these findings support the results of a number of trials of omega-3 fatty acids in pregnancy in higher income settings. It is particularly important to see if we can replicate these findings in low- and middle-income countries where the majority of preterm births occur and where infant mortality is the highest,” explains Thorne-Lyman. 

“These compelling results support the potential role of omega-3 fatty acids EPA+DHA in interventions to reduce preterm birth,” said Jillian Fry, PhD, the Director of the Seafood, Public Health & Food Systems Project at the Johns Hopkins Center for a Livable Future and an assistant scientist in the Environmental Health and Engineering Department at the Bloomberg School. She was not involved with the study. “Global seafood supplies are limited, and gaining a clearer understanding of the effect of seafood consumption and fish oil supplements on various health outcomes better informs evidence-based public health advice. For example, whereas a recent literature review indicates that 1-2 servings of seafood per week improves cardiovascular health, another review concludes that fish oil supplements do not have a consistently positive effect on cardiovascular health outcomes. This study contributes to our understanding of the relationship between EPA+DHA and preterm birth, and raises important questions about whether dietary changes or supplements are needed among pregnant women at risk of preterm delivery.”

“Plasma Concentrations of Long Chain N-3 Fatty Acids in Early and Mid-Pregnancy and Risk of Early Preterm Birth,” was written by Olsen S.F., Halldorsson T.I., Thorne-Lyman A.L.,  Strøm M.,  Gørtz S., Granstrøm C., Nielsen P.H., Wohlfahrt J., Lykke J.A., Langhoff-Roos J., Cohen A.S., Furtado J.D., Giovannucci E.L., Zhou W.

Support for this study came from March of Dimes Birth Defects Foundation (6-FY-96-0240, 6-FY97-0553, 6-FY97-0521, 6-FY00-407), Innovation Fund Denmark (‘Centre for Fetal Programming’, 09-067124), Danish Council for Independent Research (1331-00229A), and the Novo Nordisk Foundation (2010-11-12 and 2009-07-28).