Pregnant women who increase their intake of omega-3 long-chain fatty acids are less likely to have a premature birth, according to a Cochrane Review published today.

Most pregnancies last between 38 and 42 weeks, but if a baby arrives before 37 weeks, the chances of poorer health for that baby increase. One in 12 babies in Australia are born prematurely – before 37 weeks.

The earlier a baby is born, the higher the risk of poor health, and a small number of babies don’t survive.

Read more: Mums and dads of very preterm babies more likely to be depressed

Some premature babies have to spend the first weeks or months of life in special intensive care units in hospital. Premature babies can develop conditions that last a lifetime, including problems with their lungs, gut, and immune system, and vision and hearing loss.

Problems with behaviour and learning are also more common in children born too early. These consequences result in substantial costs to health care systems and to families of premature babies.

What did we find?

The Cochrane Review, led by our research team at the South Australian Health and Medical Research Institute, included 70 randomised trials with nearly 20,000 women.

It found increasing the daily intake of omega-3 long-chain fatty acids during pregnancy:

• lowers the risk of having a premature baby (birth before 37 weeks) by 11%, from 134 per 1,000 to 119 per 1,000 births

• lowers the risk of having an early premature baby (birth before 34 weeks) by 42%, from 46 per 1,000 to 27 per 1,000 births.

Most of the trials were conducted in high-income countries (Australia, the United States, England, The Netherlands and Denmark) and included women who were both at normal and high risk for poor pregnancy outcomes. Most women studied were pregnant with one baby.

The trials generally used supplements containing the omega-3 long-chain fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA).

Risk of premature birth

The causes of premature birth are still not well understood. But we know that when a pregnant woman’s labour starts, powerful hormones called prostaglandins take hold.

Sometimes women produce high amounts of prostaglandins, and those produced from omega-6 fats can make birth come too early.

Read more: Despite new findings, the jury is still out on whether omega-3 supplements reduce heart attacks

So where does omega-3 come in?

In the 1980s, researchers noticed women in Denmark had shorter pregnancies and more premature babies than their neighbours in the Faroe Islands who eat much more fish. The omega-3 long-chain fatty acids in fish seemed to be responsible – they are thought to help prevent premature birth by reducing the potency of prostaglandins that can trigger early birth.

Our review shows supplementation with omega-3 long-chain fatty acids during pregnancy is one of the few safe and effective strategies capable of preventing early labour and premature birth.

Fish or supplements?

Most of the trials included in this Cochrane review that reported on premature birth used omega-3 supplements, rather than dietary changes.

It is difficult to get the amount of the omega-3 long-chain fatty acids used in the many trials from food alone, unless you regularly eat fatty fish such as salmon, sardines or mackerel. To get the recommended amount of DHA that was used in many trials, you would need to eat at least two to three 150g serves of salmon every week.

The advice for pregnant women expecting a single baby is to consume daily fish oil supplements containing at least 500mg of DHA, starting at 12 weeks of pregnancy. The supplement does not need to contain more than 1000mg DHA+EPA. There appears to be no extra benefit of higher doses.

This advice is currently being integrated into national clinical practice pregnancy guidelines.

Read more: You can't rely on fish oil supplements in pregnancy to make your children smarter

Philippa Middleton receives funding from the NHMRC.

Maria Makrides receives funding from National Health and Medical Research Council. She is President Elect of International Society for the Study of Fatty Acids and Lipids (ISSFAL).

Jamie De Seymour and Lucy Simmonds do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.