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.