THURSDAY, May 25 (HealthDay News) -- Researchers say they've found the first evidence directly linking assisted reproductive techniques, such as in vitro fertilization, to an increased risk of a potentially dangerous complication called placenta previa.

In placenta previa, the placenta covers or partially covers the cervix, blocking a baby's passage into the birth canal. It can cause serious or life-threatening complications, including hemorrhage and the need for Caesarean section in mothers, and prematurity and perinatal problems in babies.

The study of more than 845,300 pregnancies in Norway between 1988 and 2002 concluded that mothers with single-baby pregnancies conceived through assisted reproductive techniques (ART) had a sixfold higher risk of placenta previa, compared with natural conception. Mothers who conceived both naturally and through ART had a threefold increased risk.

"What this means in absolute terms is that, after adjusting for factors such as maternal age, which tends to be higher in ART pregnancies, the risk of placenta previa rose from about three in 1,000 births to 16 in 1,000 births for ART pregnancies compared with the general population," study author Dr. Liv Bente Romundstad, of the department of obstetrics and gynecology at St. Olavs University Hospital in Trondheim, said in a prepared statement. Risk for placenta previa rose "from about seven in 1,000 births to 20 in 1,000 births for those who had both assisted and natural conceptions," she added.

Some previous studies have suggested an association between ART and increased risk of placenta previa, but the Norwegian researchers say their study is most extensive and the first to indicate a direct link.

They're calling on ART centers worldwide to collect more data on the potential problem.

"Although the risk of placenta previa is considerably higher with ART, it is still quite rare, which means it will probably take several thousand pregnancies to get sufficient data to be able to make any definite recommendations about clinical practice," Romundstad said.

The findings appear in the current issue of Human Reproduction.

More information

The U.S. National Library of Medicine has more about placenta previa.

-- Robert Preidt

SOURCE: European Society of Human Reproduction and Embryology, news release, May 25, 2006

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