Can fish oil prolong pregnancy?

Fish-oil capsules taken during the third trimester of pregnancy may extend gestation, according to a new study. If scientists confirm that preliminary finding, doctors may one day prescribe fish-oil supplements or recommend a fish-rich diet for pregnant women at risk of delivering a premature baby.

Epidemiologist Sjurdur F. Olsen at the University of Aarhus in Denmark and his colleagues began their experiment with the knowledge that women living in the harsh Faroe Islands -- a group of Danish islands in the North Atlantic -- experience longer-than-average preganancies. The team speculated that the islanders' diet, which includes a lot of fish, plays a role in extending gestation by several days. Olsen thinks the omega-3 fatty acids in fish may influence the onset of labor.

To test that theory, the team recruited 533 healthy Danish women in their third trimester. They randomly assigned 266 of them to a treatment group that received daily capsules containing omega-3 fatty acids. A control group of 136 women got daily capsules containing olive oil. The remaining 131 women served as a second control group and received no capsules.

Pregnancies in the fish-oil group lasted an average of four days longer than those in the olive-oil group, the researchers found. Fish-oil babies also averaged about 107 grams heavier than their olive-oil peers. Olsen says fish-oil babies put on the weight simply because they stayed in the womb longer.

Pregnancies in the control group that got no capsules lasted about 2.4 days longer than those in the olive-oil group. Olsen says women in the no-treatment group may have been adding fish to their diet during the study because of the perceived health benefit of a fishy diet. By contrast, the olive-oil group didn't know whether their capsule contained fish or olive oil and thus were less likely to boost their fish consumption.

When the researchers divided the women into groups based on how much fish they included in their diet at the study's start, they discovered that women who reported consuming the least amount of fish showed the biggest response to fish-oil supplementation. Women in that group had pregnancies that lasted more than a week longer than women in the same low-fish category who were assigned to the olive-oil group.

Nobody understands the mechanism behind fish-oil's action, but Olsen speculates that the omega-3 fatty acids in fish may affect the body's production of prostaglandins, a group of hormone-like substances involved in pregnancy duration.

The new study, reported in the April 25 LANCET, focused on healthy women, Olsen notes. So scientists don't know if fish-oil capsules would benefit women at risk of preterm delivery. The Danish team plans a second fish-oil study that will enroll women with a history of premature delivery, he says. Babies delivered prematurely often suffer from serious health problems.

Until the additional data come in, Susan E. Carlson, a fish-oil researcher at the University of Tennessee in Memphis, warns pregrant women against popping fish-oil capsules. Such supplementation might cause complications, she speculates.

Another fish-oil expert, Artemis P. Simopoulos of the Center for Genetics, Nutrition and Health in Washington, D.C., agrees. However, Simopoulos believes that further research will eventually prove fish oil's benefits. While she shies away from recommending fish-oil's tablets, she says pregant women can increase their consumption of fish. Nobody knows whether that strategy will prevent preterm labor, Olsen says. However, eating more fish will -- at the very least -- provide a delicous addition to help vary the diet, he says.