Uterine Fibroids and Pregnancy: How Do They Affect Each Other?

The present narrative review is aimed to rekindle discussion regarding whether and how uterine leiomyoma and pregnancy may impact each other. Although fibroids are hormone-dependent lesions, their growth during pregnancy seems to have a nonlinear trend. Besides placental estrogens and progesterone, an array of endocrine and paracrine factors affect fibroid blood supply, growth rate, and risk of degeneration along the gestational and puerperal periods. According to current evidence, the presence of leiomyomas might increase the risk of some adverse pregnancy outcomes. Although a causative relation between fibroids and spontaneous abortion is questionable, the presence of multiple submucosal lesions in certain populations, such as infertile women, may increase the risk of pregnancy loss. Slightly increased risks of placenta previa, placental abruption and fetal malpresentation may occur, mainly due to the mechanical influence of multiple and large fibroids. Cesarean section and preterm birth rates are also probably increased in the presence of fibroids. The risk associations are based on meta-analyses of cohort studies (level of evidence 2a), retrospective cohort studies (2b), case-control (3a), and cross-sectional studies (3b), but with a predominantly low risk of bias. For evaluating the growth pattern of leiomyomas and their real influence on obstetric outcomes, future studies should enroll women with fibroids diagnosed prior to pregnancy and follow them prospectively throughout the gestation and puerperium.