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

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). 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. 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. 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. This study investigated whether uterine fibroids increase the risk of miscarriage in women attending an Early Pregnancy Unit in the United Kingdom. Researchers followed 416 women with pregnancies under 10 weeks, including 104 women with fibroids and 312 women without fibroids. Pregnancy loss before 24 weeks was compared between the groups. Women with fibroids had a higher miscarriage rate than those without fibroids; however, after accounting for maternal age, fibroids were not independently associated with miscarriage. In this study, increasing maternal age was the strongest predictor of miscarriage, whilst prenatal vitamin use was associated with a lower risk. There was no association between fibroid size, location or uterine volume and miscarriage; however, having a greater number of fibroids showed a possible association. Women with fibroids were more likely to experience pain in the second trimester. Women with fibroids can be advised that maternal age appeared to be a more important predictor of miscarriage than fibroid status in this study. However, based on this study, a small to moderate effect of fibroids on miscarriage cannot be completely ruled out, and larger studies are needed to confirm these findings and assess the impact of specific fibroid characteristics.