One-thousand milligrams of docosahexaenoic acid, or DHA, per day during pregnancy has been linked with a lower rate of early preterm births in some women, compared with a lower dose common in prenatal supplements.

Researchers, who published their findings May 17 in EClinicalMedicine, looked at the rate of preterm births in U.S. women who took either 200- or 1,000-milligram supplements of DHA, an omega-3 fatty acid. The higher dose was most effective in reducing early preterm births in women who had low DHA levels at the start of the study.

"Many women in the United States and probably in many parts of the world would likely benefit from having a higher dose of DHA than what's in our current prenatal [supplements]," said Susan E. Carlson, the study's lead author and a professor of dietetics and nutrition at the University of Kansas Medical Center. 

Preterm births occur before 37 weeks of pregnancy, while early preterm birth refers to those that occur before 34 weeks. Preemie babies can have breathing, heart, developmental and immune complications and face a greater risk of long-term disabilities and death.

Preterm births are difficult to predict, although a recent study found that blood biomarkers could help pinpoint a woman's due date. 

Some studies indicated that DHA supplements during pregnancy could help reduce preterm births, but the optimal dose has not been established. According to Carlson, most prenatal supplements in the U.S. contain 200 milligrams, but the researchers suspected that higher doses could be better at reducing early births.

Carlson and her colleagues recruited 1,100 women at three medical centers in the U.S. who were older than 18 and were between 12 and 20 weeks along in their pregnancies. The women were instructed to take capsules containing either 200 or 1,000 milligrams of DHA each day.

"About half the women that enrolled in the study were already taking DHA as a supplement. So we didn't want to ask them to stop taking it, because there was already evidence that it would be helpful," Carlson told The Academic Times. "We just didn't know if more would be better."

The results suggest that is indeed the case. For women who entered the study with low DHA levels, in the high-dose group, the rate of early preterm births was half that of the low-dose group: 2%, compared with 4.1% in women who took only 200 milligrams.

For women who entered the study with high DHA levels, the early preterm birth rate was very low, at just 1.2%, and there was no appreciable difference between those taking the low- and high-dose supplements.

The findings line up with a similar Australian study, which found that in women with low DHA levels, the group that took a supplement that contained 800 milligrams of DHA and 100 milligrams of another omega-3 called eicosapentaenoic acid had fewer preterm births than women who took a placebo.

The World Health Organization currently recommends between 300 and 1,000 milligrams of DHA per day during pregnancy, according to Carlson. 

"But in the United States, we do not have any recommendations for DHA for pregnancy or any other purpose, and one of the reasons is that we have not had studies that convinced anyone that it was beneficial," she said. "I'm hoping this study goes some way toward making some recommendations for pregnant women."

For now, she suggests that women talk to their physicians about taking DHA supplements during pregnancy. For example, women who have low DHA levels or have previously had a preterm birth might benefit from taking a high dose.

In ongoing work, Carlson and her colleagues are developing food questionnaires to assess women's DHA intake from their diets. This omega-3 fatty acid is found in eggs and fish, particularly oily fish such as salmon and tuna.

"Our goal is to see if we can develop a pragmatic way to help obstetricians know who has low [DHA] status and who they could then recommend a higher dose to," she said.

The mechanism by which DHA could prevent preterm birth is not entirely clear.

"We do know that DHA is a precursor for resolvins and maresins, which are agents in our body that shut down inflammation," Carlson said. "Our hypothesis is that this could be one of the mechanisms by which preterm birth is reduced, but that would assume that there's some kind of inflammatory process going on that leads to preterm birth, which is not necessarily confirmed."

"There's probably more than one mechanism for early preterm birth," she continued. "And maybe DHA addresses [at least] one of those." 

Certain factors, such as race, age, stress levels and tobacco use, increase the risk of early labor. In the U.S., Black women are about 50% more likely to have a preterm birth than their Hispanic or white peers. 

The researchers sought to include diverse women in their study; the group was about 50% white, 22% Black and 22% Hispanic. According to Carlson, the results indicate that DHA is beneficial regardless of race or ethnicity, but the team plans to dig deeper into differences among races in future analyses. 

In many nutritional studies, there are some people who don't take all the capsules, a problem known as noncompliance. At the end of the study, the researchers asked participants to mail back unconsumed capsules so that the scope of this issue could be assessed. They will report those findings in a forthcoming study. 

"We're working on compliance," Carlson said. "Part of that is education — being able to tell people that DHA will likely help them. But we have to get the message out to women that DHA is important."

Carlson said that women who have lower socioeconomic status are often the least compliant.

"Reaching that group of women — who actually have the highest rate of early preterm birth — is always a challenge," she said, "but one that we want to work on."

The study, "Higher dose docosahexaenoic acid supplementation during pregnancy and early preterm birth: a randomised, double-blind, adaptive-design superiority trial," published May 17 in EClinicalMedicine, was authored by Susan E. Carlson, Byron J. Gajewski, Elizabeth H. Kerling, Carl P. Weiner, Scott A. Sands, Alexandra R. Brown, Dinesh Pal Mudaranthakam and Sarah A. Crawford, University of Kansas Medical Center; Christina J. Valentine and Emily A. DeFranco, University of Cincinnati; Michael Cackovic, Ohio State University; Catalin S. Buhimschi, University of Illinois; and Lynette K. Rogers, Nationwide Children's Hospital.