The largest study of its kind to date revealed that the presence of fibroid tumors did not increase risk of miscarriage, contradicting common beliefs of women and care providers.
Findings by the research team, led by scientists at Vanderbilt University and including NIEHS reproductive epidemiologist Donna Baird, Ph.D., may reduce unnecessary surgery for women with fibroids who plan to become pregnant. The new paper appeared June 7 in the American Journal of Epidemiology.
The research team wanted to learn more about the type and size of fibroids that are most likely to be associated with miscarriage, according to lead author Katherine Hartmann, M.D., Ph.D., from Vanderbilt. The goal was to better understand who might benefit most from surgery to remove fibroids before a future pregnancy.
However, results did not support earlier studies that pointed to fibroids’ alteration of uterine shape or size as a risk factor for miscarriage. "Women with fibroids had identical risk of miscarriage as women without fibroids, when taking into account other risks for pregnancy loss," Hartmann reported in a Vanderbilt press release. "We were stunned."
Her reaction hints at how deeply the conventional wisdom about fibroids and pregnancy is held among health professionals. Yet, according to the authors, the study confirmed several meta-analyses of clinical trials, one as recent as 2012, which found that removing fibroids had no effect on rates of miscarriage. The authors suggested several reasons for the surprising findings.
- Unlike earlier studies, the team used research ultrasound to systematically document the fibroid status of all participants.
- The research team enrolled a large, racially diverse group of women, living in and near eight cities across three states.
- Their statistical analyses accounted for age and race, because fibroids increase with age, and African American women experience a higher prevalence of fibroids.
Fibroids and complications
Fibroid tumors in the uterus are benign growths that occur more frequently as women get older. The authors explained that until now, scientists thought that the location or size of a fibroid could interfere with attachment of the embryo, cramping of the uterus, or function of the placenta. As a result, surgery may be recommended for women with fibroids before they attempt to get pregnant, especially if a previous pregnancy ended in miscarriage.
"Current clinical wisdom purports that fibroids are a cause of miscarriage and prominent professional organizations, such as the American Society of Reproductive Medicine, endorse intervention," they wrote.
Yet when the more than 5,500 women enrolled were divided into two groups, according to whether fibroids were detected in ultrasounds, the team observed the same rate of miscarriage in both groups — 11 percent. The authors advised that surgical removal of fibroids to reduce risk of miscarriage should receive careful scrutiny.
"This study addressed an important question with state-of-the-art methods," said Dale Sandler, Ph.D., head of the NIEHS Epidemiology Branch. "The authors carefully considered all potential challenges to the validity of their findings, concluding rightly that their work calls into question a long-held belief in clinical practice."
Study volunteers were part of Right from the Start: A Study of Early Pregnancy, funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development.
Citation: Hartmann KE, Velez Edwards DR, Savitz DA, Jonsson-Funk ML, Wu P, Sundermann AC, Baird DD. Prospective cohort study of uterine fibroids and miscarriage risk. Am J Epidemiol; doi: 10.1093/aje/kwx062 [Online 7 June 2017].