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 pregnancy from communities in 3 states. 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.

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