Fibroids are quite often discovered on a sonogram after a woman becomes pregnant, and they are associated with an increased likelihood of complications such as cesarean delivery, breech presentation and preterm birth.

Those findings come from Dr. Alison F. Jacoby and colleagues from the University of California, San Francisco, who compared outcomes in more than 15,000 pregnant women with or without fibroids discovered during a routine second trimester sonogram.

A little less than 3 percent of the women had at least one fibroid of 1 centimeter or more in size, with most women having only one fibroid, the investigators report in the medical journal Obstetrics & Gynecology.

Women with fibroids had a 64 percent increased risk of having a cesarean delivery, a 59 percent increased risk of the baby being malpositioned, and a 45 percent increased risk of delivering before term, the authors report.

Also, the likelihood of severe post-birth bleeding went up 157 percent.

Overall cesarean delivery rates did not differ significantly between women with larger fibroids (10 cm or greater) and women with smaller fibroids, the researchers note, but women with larger fibroids were more likely to have malpresentation.

“The biologic basis for the association between (fibroids) and obstetric complications is unclear, although physical interference leading to decreased uterine distensibility or mechanical obstructions likely plays a role,” Jacoby and colleagues point out.

SOURCE: Obstetrics & Gynecology, February 2006.