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Pregnancy in women with uterine leiomyomas (fibroids)

David W Ouyang, MD
Errol R Norwitz, MD, PhD, MBA
Section Editor
Charles J Lockwood, MD, MHCM
Deputy Editor
Vanessa A Barss, MD, FACOG


Uterine fibroids (leiomyomas) are benign smooth muscle tumors of the uterus. The potential effects of fibroids on pregnancy and the potential effects of pregnancy on fibroids are a frequent clinical concern since these tumors are common in women of reproductive age. Most pregnant women with fibroids do not have any complications during pregnancy related to the fibroids. Pain is the most common problem, and there may be a slightly increased risk of obstetrical complications such as miscarriage, premature labor and delivery, abnormal fetal position, and placental abruption.

This topic will review issues specifically relating to pregnant women with uterine fibroids. Fibroids in nonpregnant women, including fertility issues, are discussed separately. (See "Uterine leiomyomas (fibroids): Epidemiology, clinical features, diagnosis, and natural history" and "Reproductive issues in women with uterine leiomyomas (fibroids)".)


Several factors make it difficult to assess the impact of fibroids on pregnancy outcome and identify specific fibroid characteristics that are important. For example, the mechanisms whereby fibroids may cause adverse obstetric outcomes are not clearly understood. In addition, available evidence is difficult to interpret due to the heterogeneity of the study populations in these reports, which differ in fibroid number, size, location (lower uterus, fundus), and type (submucosal, intramural, or subserosal; pedunculated or sessile); gestational age at diagnosis; and method of ascertainment (eg, prospective versus retrospective study design). Lastly, small fibroids (<4 to 5 cm) may not be detected consistently because they can be difficult to distinguish from physiologically thickened myometrium.


The prevalence of uterine fibroids in pregnancy varies between 1.6 and 10.7 percent, depending upon the trimester of assessment and the size threshold [1-5]. In one study, 4 percent of 12,708 pregnant patients had fibroids with a diameter >3 cm [2]. In another, 1.6 percent of 12,600 consecutive pregnant patients had fibroids >1 cm [3]. A third series in over 15,000 women with nonanomalous singleton pregnancies undergoing routine second trimester ultrasonography reported that 2.7 percent had fibroids ≥1 cm [1]. A fourth series of 4271 first trimester or post-miscarriage ultrasound examinations observed 10.7 percent of women had a fibroid of ≥0.5 cm [4]. (See "Uterine leiomyomas (fibroids): Epidemiology, clinical features, diagnosis, and natural history", section on 'Prevalence'.)

The prevalence of fibroids increases with age and is higher in African-American women than in white or Hispanic women [4]. Increasing parity and prolonged duration of breastfeeding are associated with a small, but statistically significant, reduction in prevalence [6].

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Literature review current through: Dec 2017. | This topic last updated: Dec 19, 2017.
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