"It's unfortunate this study is a negative finding, but I don't think it closes the door to looking further," said Dr. Tiffany Moore Simas, an associate professor of obstetrics and gynecology at the University of Massachusetts Medical School in Worcester, who was not involved in the study.

Left untreated, gestational diabetes and preeclampsia can lead to serious -- or even fatal -- complications for both mother and child.

Women with gestational diabetes are more likely to develop type 2 diabetes later in life and their children are at increased risk of obesity and insulin resistance, a diabetes precursor. Between three and eight percent of pregnant women in the U.S. develop gestational diabetes.

Preeclampsia, which causes high blood pressure as well as excess protein in the urine, may necessitate early delivery of the baby. The disorder is estimated to cause 18 percent of all maternal deaths in the U.S.

Previous research has led to conflicting claims about the benefits of fish oil for pregnant women. Because there's evidence omega-3s may improve blood sugar control and vascular health in general, Australian researchers set out to see whether fish oil might offer some protection during pregnancy.

For the new study, published in the American Journal of Clinical Nutrition, Maria Makrides at the University of Adelaide and her colleagues tracked data on 2,400 women recruited from five pregnancy centers between October 2005 and January 2008.

All study participants received three daily capsules containing either fish oil rich in docosahexaenoic acid (DHA), an omega-3, or a blend of three vegetable oils. Neither the subjects nor the study staff knew who was taking which type of capsule.

Overall, eight percent of the participants developed gestational diabetes and five percent developed preeclampsia.

Women who took the fish oil supplement had a three percent lower risk of gestational diabetes and 13 percent lower risk of preeclampsia than those who received the vegetable oil pills.

But that difference was not considered statistically significant, meaning it could have happened by chance.

"There's no need to take fish oil if your outcome is to prevent gestational diabetes or preeclampsia," said Makrides.

When her team analyzed birth complications, however, they found three deaths and no convulsions among infants whose mothers took fish oil, compared with 12 deaths and five convulsions in the placebo group. This "requires further investigation," they wrote.

"It did reduce the rate of early pre-term births," which led to fewer admissions to neonatal intensive care among babies in the fish oil group, Makrides told Reuters Health.

Simas noted that the women in the study started taking fish oil capsules only after 20 weeks of pregnancy, but a much earlier start might show a different and possibly beneficial effect on gestational diabetes and preeclampsia.

"Both… are significantly related to the placenta, and your placenta starts growing very early in pregnancy," Simas told Reuters Health.

Many women take these supplements during pregnancy in the belief that DHA can aid in a baby's brain development.

A large study, also by Makrides, published in The Journal of the American Medical Association in 2010 found no evidence of a benefit.

Still, fish oil is safe and has few known downsides, Simas pointed out.

"I would continue to recommend taking fish oil supplements," she said.

SOURCE: bit.ly/Kcz8r6 The American Journal of Clinical Nutrition, online May 2, 2012.

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