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.
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.
So scientists don't know if fish-oil capsules would benefit women at risk of preterm delivery.
Carlson, a fish-oil researcher at the University of Tennessee in Memphis, warns pregrant women against popping fish-oil capsules.
In the past decade, studies have shown that fish-oil fatty acids seem to protect against atherosclerosis, a fatty buildup on artery walls.
Milner of the Washington (D.C.) Hospital Center and his colleagues report that large fish-oil doses can "dramatically improve" the results of angioplasty.
Those in the fish-oil group took nine capsules containing 4.5 grams of omega-3 fatty acids per day for six months -- the daily equivalent of that found in about two cans of sardines.
"The control group had a 35.4 percent reocclusion rate and the fish-oil group had only a 19 percent reocclusion rate."