Small uterine fibroids are associated with an increased risk of miscarriage

Apr 13 2004

Fibroids, benign muscle tumors of the uterus, are estimated to affect more than one in five women of reproductive age. But little is known about the influence of these growths on pregnancy outcomes, including miscarriage, premature birth and fetal growth restriction.

"No studies have prospectively investigated these risks in a large cohort of women early in pregnancy where presence of fibroids was uniformly assessed using ultrasound imaging. This is the first large-scale prospective study to do that," said Dr. Katherine Hartmann, the study's principal investigator. Hartmann also is assistant professor of obstetrics and gynecology as well as epidemiology in UNC's schools of medicine and public health.

"Fibroids are very common, as are these potentially devastating pregnancy outcomes. But research evidence to inform clinical care is meager," she said.

Previous ultrasound studies of uterine fibroids were flawed because they used ultrasound databases including fibroids that doctors considered of concern, Hartmann said. Typically, these were fibroids of at least three centimeters. Others, often much smaller, were not uniformly noted.

"So the studies are flawed by inadequate assessment of the classification of who has fibroids and who does not," she said. "In our pilot study of 1,600 women, we discovered that the majority of those who have fibroids never have been told that they did."

Fibroids were diagnosed in 170 of the women.

Pilot study results show that women with fibroids have a 55 percent increased risk of pregnancy loss, and smaller fibroids are significantly more associated with having a miscarriage than larger ones. Moreover, it appears that presence of fibroids is uniformly associated with miscarriage throughout early pregnancy.

Hartmann recently presented the pilot study findings at the 2004 Annual Meeting of the Society for Gynecologic Investigation in Houston.

During the next five years, funded by a $3 million grant from the National Institute for Child Health and Human Development, Hartmann's UNC research team will enroll an additional 3,300 ethnically diverse women from 15 N.C. counties who are either planning a pregnancy or are in the early weeks of pregnancy.

The study will also explore the influence of pregnancy and events after pregnancy on fibroid growth. With more than 5,000 women enrolled, the study will have the statistical power to more effectively examine the impact of race, maternal age and smoking status on pregnancy outcome in women with and without fibroids, Hartmann said.

The study's strengths include use of sequential ultrasound exams to assess the presence, location and growth of fibroids, and a proven community recruitment plan dedicated to including at least 15 percent Hispanic and 35 percent black women, Hartmann said.

The Center for Women's Health Research, directed by Hartmann, will enroll study participants.

"This is an ideal example of a study that follows from the center's mission of advancing the health of all women through research," she said. "It is imperative to promote multidisciplinary research that gets solid answers from the use of sophisticated research methods."

Co-investigators with Hartmann include Dr. David Savitz, professor and chair of epidemiology; Dr. Amy Herring, assistant professor of biostatistics; and Dr. Donna Baird of the National Institute for Environmental Health Sciences.

The Center for Women's Health Research is a collaborative UNC effort of the School of Medicine, led by the department of obstetrics and gynecology; the School of Public Health, led by the department of epidemiology; and the Cecil G. Sheps Center for Health Services Research.