Fibroids and the risk of miscarriage: a prospective observational study in an early pregnancy population

Background The impact of fibroids on pregnancy outcomes has been studied extensively in the context of in vitro fertilisation; however, evidence in the general obstetric population is limited. No prospective studies from the United Kingdom have examined the relationship between fibroids and early pregnancy loss in a mixed population. This study evaluated the association between fibroids and miscarriage in women presenting to an Early Pregnancy Unit (EPU).Methods Prospective observational study conducted over 15 months, involving 416 women with singleton pregnancies <10 weeks’ gestation at a London tertiary EPU. Participants with fibroids (n = 104) were compared with controls (n = 312); all underwent systematic ultrasound, and confounder data were collected. The primary outcome was miscarriage before 24 weeks; secondary outcomes included gestation of miscarriage, second-trimester pain and bleeding.Results Miscarriage occurred in 65 women: 22.9% with fibroids versus 14.6% without (unadjusted odds ratio [OR] 1.74, 95% CI 0.98–3.10; p = .059); after adjustment, the association was attenuated (adjusted OR [aOR] 1.49, 95% CI 0.82–2.70; p = .19). Increasing fibroid number was associated with higher risk (OR per additional fibroid 1.17, 95% CI 1.01–1.37; p = .04). First-trimester miscarriage was higher with fibroids (unadjusted relative risk ratio [RRR] 1.99, 95% CI 1.09–3.61, p = .024); although this association was attenuated with age (aOR 1.59, 95% CI 0.86–2.93, p = .14; adjusted RRR 1.63, 95% CI 0.88–3.04, p = .12). Other fibroid characteristics and uterine volume did not significantly influence miscarriage risk. Second-trimester pain was more common with fibroids (OR 2.92, 95% CI 1.43–5.97, p < .05); there was no difference in bleeding.Conclusion A higher miscarriage rate was observed with fibroids; however, there was no independent association after adjustment. Our study was underpowered to detect a small difference in miscarriage rate. Women of advanced maternal age can be counselled that their risk of miscarriage is influenced more by age than the presence of fibroids.