Cochrane for Clinicians

Putting Evidence into Practice

Antepartum Omega-3 Fatty Acid Intake and Length of Gestation


Am Fam Physician. 2020 Jan 1;101(1):17-18.

Clinical Question

Are omega-3 fatty acids safe and effective for reducing the risk of preterm birth (before 37 weeks’ gestation) and early preterm birth (before 34 weeks’ gestation)?

Evidence-Based Answer

Omega-3 fatty acids, whether taken as supplements or consumed as part of the diet, reduce the risk of preterm birth (number needed to treat = 68) and early preterm birth (number needed to treat = 55). However, they also increase the risk of prolonged gestation (more than 42 weeks; number needed to harm = 102).1 (Strength of Recommendation: A, based on consistent, good-quality patient-oriented evidence.)

Practice Pointers

Preterm birth accounts for 85% of perinatal complications and deaths,2 and the percentage is increasing in the United States.3 Previous observational and cohort studies have suggested that omega-3 fatty acid intake can reduce the risk of preterm birth.1 A recent study in Norway evaluated food and supplement intake in a cohort of 67,000 pregnant women. It showed that seafood consumption was associated with a lower prevalence of preterm delivery, whereas use of omega-3 supplements resulted in a lower prevalence only of early preterm delivery.4 (The authors did not specify the type of seafood consumed.) The anti-inflammatory properties of omega-3 fatty acids may be the mechanism by which intake influences delivery timing.1 The primary outcomes discussed in this review were preterm birth, early preterm birth, and prolonged gestation in relation to omega-3 fatty acid intake in any form. The authors also investigated a number of secondary outcomes involving maternal, perinatal, neonatal, and child health.

This Cochrane review, which included 70 randomized controlled trials and 19,927 women, compared omega-3 fatty acid intake to placebo or no intake.1 Omega-3 fatty acid intake involved using supplements, eating foods rich in omega-3 fatty acids, or receiving advice to consume these types of foods. The studies included women at low, high, and mixed risk of poor pregnancy outcomes based on a combination of factors, including history and age. Most of the studies investigated the effect of omega-3 fatty acids in the form of supplements. The study-level risk of bias was mixed. Most trials were conducted in upper-middle income or high-income countries, with the highest number conducted in the United States.

Patients who used omega-3 fatty acids demonstrated a reduced risk of preterm birth (11.9% vs. 13.4% in those who did not use them; relative risk [RR] = 0.89; 95% CI, 0.81 to 0.97), as well as a reduced risk of early preterm birth (2.7% vs. 4.6%; RR = 0.58; 95% CI, 0.44 to 0.77). A subgroup analysis showed a decreased risk of prelabor rupture of membranes in those using omega-3 fatty acids (RR = 0.46; 95% CI, 0.28 to 0.76; four trials; 1,281 participants). However, omega-3 fatty acid intake increased the risk of prolonged gestation (2.6% vs. 1.6%; RR = 1.61; 95% CI, 1.11 to 2.33).

The studies also demonstrated a reduced risk of low birth weight with omega-3 fatty acids (14% vs. 15.6%; RR = 0.90; 95% CI, 0.82 to 0.99). There were no statistically significant differences in maternal outcomes. In addition, the authors evaluated a variety of neurodevelopmental and growth outcomes in children but concluded that there were no differences between those who were treated and those who were not.

The 2012 American College of Obstetricians and Gynecologists practice bulletin, “Prediction and Prevention of Preterm Birth,” does not make a recommendation about using omega-3 fatty acids to prevent preterm birth.5 Since then, several systematic reviews and meta-analyses have been published about whether supplementation decreases the risk of preterm birth. The results of three studies were consistent with those of the Cochrane review in demonstrating that omega-3 fatty acids reduce the risk of preterm birth,68 but two other

Author disclosure: No relevant financial affiliations.


show all references

1. Middleton P, Gomersall JC, Gould JF, et al. Omega-3 fatty acid addition during pregnancy. Cochrane Database Syst Rev. 2018;(11):CD003402....

2. Thornton S. Preterm birth: causes, consequences and prevention. Obstet Gynaecol. 2008;10(4):280.

3. Martin JA, Hamilton BE, Osterman MJK, et al. Births: final data for 2016. Natl Vital Stat Rep. 2018;67(1):1–55.

4. Brantsæter AL, Englund-Ögge L, Haugen M, et al. Maternal intake of seafood and supplementary long chain n-3 poly-unsaturated fatty acids and preterm delivery [published correction appears in BMC Pregnancy Childbirth. 2017;17(1):61]. BMC Pregnancy Childbirth. 2017;17(1):41.

5. Committee on Practice Bulletins—Obstetrics, American College of Obstetricians and Gynecologists. Practice bulletin no. 130: prediction and prevention of preterm birth. Obstet Gynecol. 2012;120(4):964–973.

6. Kar S, Wong M, Rogozinska E, et al. Effects of omega-3 fatty acids in prevention of early preterm delivery: a systematic review and meta-analysis of randomized studies. Eur J Obstet Gynecol Reprod Biol. 2016;19840–46.

7. Imhoff-Kunsch B, Briggs V, Goldenberg T, et al. Effect of n-3 long-chain polyunsaturated fatty acid intake during pregnancy on maternal, infant, and child health outcomes: a systematic review. Paediatr Perinat Epidemiol. 2012;26(suppl 1):91–107.

8. Chen B, Ji X, Zhang L, et al. Fish oil supplementation improves pregnancy outcomes and size of the newborn: a meta-analysis of 21 randomized controlled trials. J Matern Fetal Neonatal Med. 2016;29(12):2017–2027.

9. Saccone G, Berghella V. Omega-3 supplementation to prevent recurrent preterm birth: a systematic review and metaanalysis of randomized controlled trials. Am J Obstet Gynecol. 2015;213(2):135–140.

10. Agency for Healthcare Research and Quality. Omega-3 fatty acids and maternal and child health: An updated systematic review. Page last reviewed August 2018. Accessed October 24, 2019.

These are summaries of reviews from the Cochrane Library.

This series is coordinated by Corey D. Fogleman, MD, assistant medical editor.

A collection of Cochrane for Clinicians published in AFP is available at



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