However, the researchers did find a "slight increase" in the risk of excessive bleeding during labor, and the failure of the uterus to contract normally after delivery, for women who used the drugs while pregnant.

Triptans are among the most powerful drugs used for migraine; others include aspirin, Excedrin, and ibuprofen.

While as many as three in 10 women may develop migraines during their childbearing years, women often shy away from using such drugs during pregnancy because of safety concerns, according to study co-author Katerina Nezvalova-Henriksen of the University of Oslo in Norway and her colleagues.

However, the authors of the study in Headache note, untreated migraine may itself carry risks for mother and child; some studies have linked it to pre-eclampsia, a potentially deadly pregnancy complication.

"While it is important to exert caution when using any medications during pregnancy, this study indicates" that pregnant women can either start or continue taking triptans without "any major risk" of miscarriage, premature delivery, or other bad outcomes, the authors conclude.

Nezvalova-Henriksen and her team studied nearly 70,000 women. Two percent, or 1,535, had used sumatriptan (Imitrex), rizatriptan (Maxalt), zolmitriptan (Zomig), or eletriptan (Relpax) in pregnancy.

Less than one percent -- 373 women -- had used the drugs before getting pregnant but not during pregnancy.

The overall birth defect rate, which encompasses everything from large birthmarks to serious heart problems, was the same among women who had taken triptans during pregnancy and those who didn't have migraines: 5 percent. Among those who had used triptans in the past but not during pregnancy, it was slightly higher: 6 percent.

The women who used triptans were also more likely than non-triptan users to take other drugs during pregnancy, including acetaminophen (Tylenol) with codeine and non-steroidal anti-inflammatory drugs such as ibuprofen.

However, the rate of major birth defects - such as serious problems of the limbs or internal organs -- was 3 percent for all three groups. That rate - about one in 33 births - is about what would be expected for all birth defects in the general population.

The researchers did find that women who used triptans in their second or third trimester were more likely to develop a condition called atonic uterus, in which the uterus fails to contract back to its normal size after delivery. This is the leading cause of excessive bleeding after delivery. They were also more likely to lose significant amounts of blood during labor and delivery.

And during pregnancy, they were more likely to suffer from vomiting than women who had never used the drug; they were also more likely to develop pre-eclampsia or eclampsia, and more likely to have deficiencies in the B-vitamin folate.

While many women who suffer migraines will experience improvements in their symptoms after their first trimester, Nezvalova-Henriksen and her team note, those whose symptoms don't improve by then aren't likely to get better.

"Although the findings are reassuring, confirmation in independent studies is warranted," the researchers conclude.

SOURCE: Headache, online January 28, 2010.