Preterm birth — delivery before 37 weeks of gestation — is the leading cause of neonatal death and the second leading cause of death in children under five worldwide. The World Health Organization estimates that 1 in 10 babies globally are born early.1 Strategies to prevent preterm birth have historically been limited. That changed with a body of evidence centred on one nutrient: omega-3 docosahexaenoic acid (DHA).
The Cochrane evidence
The landmark 2018 Cochrane Review by Middleton and colleagues examined 70 randomised controlled trials involving 19,927 women. The findings were unequivocal: pregnant women assigned to increase omega-3 intake (through food or supplementation) had an 11% reduction in all-cause preterm birth at less than 37 weeks (RR 0.89, 95% CI 0.81–0.97) and a 42% reduction in early preterm birth at less than 34 weeks (RR 0.58, 95% CI 0.44–0.77).2
These results were rated as high-quality evidence. The review authors stated that additional placebo-controlled trials were very unlikely to change the confidence in this estimate — an unusually strong conclusion for a Cochrane review. The effect was driven predominantly by trials providing more than 500 mg per day of DHA.2
Two subsequent large-scale RCTs confirmed that the benefit is greatest in women with low baseline omega-3 levels. The Australian ORIP trial (5,544 women) found that supplementation with 800 mg DHA plus 100 mg EPA significantly reduced early preterm birth in women with low omega-3 status, while women already consuming adequate omega-3 showed no additional benefit.3
Clinical guidelines: where we are now
In 2024, the European Board and College of Obstetrics and Gynaecology (EBCOG) published a formal position statement establishing clinical practice guidelines for omega-3 supplementation during pregnancy. The statement called for identification of women at increased risk of preterm birth due to low DHA intake and recommended supplementation to reduce that risk.4
The International Society for the Study of Fatty Acids and Lipids (ISSFAL), in a 2022 consensus statement, recommended that women with low omega-3 status supplement with approximately 1,000 mg of DHA plus EPA, preferably starting before 20 weeks' gestation.5
In April 2025, the NIH Office of Dietary Supplements updated its guidance, stating that experts recommend all women of childbearing age consume at least 250 mg per day of DHA plus EPA, with an additional 100–200 mg of DHA during pregnancy. The NIH explicitly recognised that omega-3 DHA supplementation reduces the risk of preterm and early preterm birth — the first time a major US government agency officially acknowledged this.6
Australia's 2021 Pregnancy Care Guidelines went further, recommending 800 mg DHA plus 100 mg EPA daily for women with low omega-3 levels — the most specific dosing guidance of any national body.7
How much and when
Based on the converging evidence from the Cochrane review, EBCOG, ISSFAL, and the NIH:
Minimum recommendation: 250 mg DHA plus EPA daily for all women of childbearing age, with an additional 100–200 mg DHA during pregnancy.6
For women with low omega-3 status or risk factors for preterm birth: 800–1,000 mg DHA (or DHA plus EPA) daily, starting before 20 weeks' gestation.5 7
Safety: The 2024 clinical practice guideline stated that 1,000 mg per day of DHA or DHA plus EPA in pregnant women did not raise safety concerns. No upper limit has been established by the NIH.6
Source matters: Most pregnant women in the United States have omega-3 intakes well below recommended levels.8 Dietary sources include fatty fish (salmon, sardines, mackerel, anchovies), but supplementation is typically necessary to reach the therapeutic doses shown to reduce preterm birth risk. Most prenatal vitamins contain 200 mg of DHA or less — well below the evidence-based threshold.
What this means for you
Check your prenatal supplement. If it contains less than 200 mg of DHA, you are below even the minimum NIH recommendation. If you have any risk factors for preterm birth, discuss higher-dose supplementation with your provider. The evidence for omega-3 DHA in preventing preterm birth is among the strongest for any single nutritional intervention in pregnancy — and most women are not getting enough.
