Do uterine fibroids increase the risk of preterm birth?

One in 10 women with singleton pregnancies have at least 1 uterine fibroid (UF), according to a prospective cohort study.

The study in the journal BMC Pregnancy Childbirth also found that 7.6% of women with singleton pregnancies have preterm birth (PTB).

However, the prevalence of UFs was comparable for women with preterm and term births: 10.2% vs. 10.3%, respectively.

The study recruited women who were pregnant or planning a pregnancy from communities in 3 states (North Carolina, Tennessee, and Texas) between 2000 and 2012.

The population comprised mostly White (71.5%) and Black, non-Hispanic women (17.4%) from a range of household income and education levels.

Overall, 48% of women were nulliparous and 8.2% reported a prior preterm birth.

In addition, 43.8% of women were overweight or obese at pregnancy onset, but only 3.5% smoked.

Participants underwent a research ultrasound in the first trimester to determine pregnancy dating and to record detailed information about the presence, size, number and location of UFs.

PTB was defined as live birth at less than 37 weeks’ gestation.

After adjusting for race/ethnicity and maternal age, UFs were not linked to an increased risk of PTB: adjusted risk ratio (aRR) 0.88; 95% confidence interval (CI): 0.62 to 1.24.

UFs were also not connected to any clinical subtype of PTB. Furthermore, no UF characteristic or combination of characteristics was associated with risk.

But women who were older than 35, Black or obese were more prone to have UFs. For instance, women in this age bracket were more than 5 times as likely to have UFs than women under the age of 25. Likewise, Black, non-Hispanic women were nearly 3 times as likely to have UFs than White, non-Hispanic women.

The average gestational age at birth for both women with and without UFs was 39 weeks and 2 days (P=.34).

Among PTBs, 88% were late preterm, defined as deliveries occurring for any indication between 34 weeks and 0 days and 36 weeks and 6 days.

PTB clinical subtype was identified in 60% of cases. PTB was secondary to spontaneous preterm labor in 39.3% of cases, followed by medically indicated delivery for maternal or fetal conditions in 37% of cases, and PTBs after preterm premature rupture of membranes (PPROM) in 23.7% of cases.

The authors did not detect an association between UF presence and medically indicated PTB or spontaneous PTB.

Findings did not change when adjusted for prior PTB.

Because the imaging was performed by experienced clinical sonographers using a detailed protocol to systematically characterize UFs, the current study is an improvement over previous studies that depend on maternal self-report, which fails to capture up to 80% of UFs, according to the authors.

“If fibroids increase risk of preterm birth, the effect is substantially smaller than previous estimates,” they wrote. “Given lack of effect in a large population of women from the general population, rather than higher risk academic tertiary populations previously most studied, we encourage a reconsideration of the clinical impression that presence of fibroids is a major risk factor for preterm birth.”

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Reference

Sundermann AC, Aldridge TD, Hartmann KE, et al. Uterine fibroids and risk of preterm birth by clinical subtypes: a prospective cohort study. BMC Pregnancy Childbirth. 2021 Aug 17;21(1):560.

doi:10.1186/s12884-021-03968-2