Uterine fibroids occur most commonly in women of reproductive age and are increasingly seen in younger women. As a result, fibroids coexisting with pregnancy is a frequent clinical scenario. The incidence of pregnancy complicated by uterine fibroids is 0.5%–1% among all fibroid patients, and 0.3%–7.2% among all pregnancies.
In recent years, delayed marriage and childbearing have led to a rise in advanced maternal age, contributing to a higher detection rate. Widespread use of prenatal ultrasound, improved diagnostic accuracy, and higher cesarean section rates have also increased identification of fibroids during pregnancy. Since most fibroids are small and asymptomatic, they are easily overlooked during labor and delivery; the true prevalence is likely higher. Pregnancy with fibroids has become an important factor affecting pregnancy outcomes, and this article aims to provide clinical guidance for affected patients.
Mutual Effects Between Fibroids and Pregnancy
Pregnancy complicated by uterine fibroids is classified as a high-risk pregnancy. Fibroids can adversely affect the pregnancy, delivery, and postpartum (puerperium) period up to 6 weeks after birth. The rate of fibroid degeneration is also significantly higher during pregnancy.
Effects of Uterine Fibroids on Pregnancy
1. Infertility
Infertility affects 20%–30% of women with fibroids, mainly because fibroids distort pelvic anatomy and impair reproductive function, hindering fertilization, implantation, and embryonic development. In many cases, fertility is restored after fibroid treatment or removal.
2. Miscarriage and Preterm Birth
The rate of spontaneous miscarriage reaches 20%–30% in women with fibroids—2–3 times higher than in unaffected pregnancies. Miscarriages are often incomplete and accompanied by heavy bleeding. In the second and third trimesters, rapid fibroid growth or degeneration may lead to preterm birth. Studies show inconsistent correlations between fibroid size/location and miscarriage risk, with most finding no strong linear relationship.
3. Placental and Fetal Malposition
Large fibroids, especially intramural or submucous fibroids, may restrict fetal movement, increasing the incidence of malpresentation such as transverse or breech lie. Fibroids also impair decidual development at the implantation site, raising risks of placenta previa, placental abruption, and placental adherence.
4. Premature Rupture of Membranes (PROM)
Fibroids may obstruct fetal descent or interfere with membrane development, leading to premature rupture of membranes.
5. Antepartum Hemorrhage
Fibroids located behind the placenta are associated with higher antepartum bleeding, which is also linked to placental abnormalities and preterm birth.
6. Pregnancy-Related Fibroid Pain Syndrome
This is the most common complication, including red degeneration, aseptic necrosis, malignant transformation, and hemorrhagic infarction. The incidence of abdominal pain reaches 25.6% when fibroids exceed 5 cm in diameter.
Effects of Uterine Fibroids on Labor
The impact depends on fibroid number, location, and size:
- Higher rates of malpresentation increase the risk of dystocia and cesarean section.
- Fibroids may disrupt uterine contractility, prolonging labor. Fibroids impacted in the pelvis—such as cervical or large lower-segment fibroids—can cause mechanical obstruction and dystocia.
- Post-delivery uterine contraction may be impaired, especially by fundal fibroids, increasing risks of placental adherence, retained placenta, and postpartum hemorrhage. Newborn outcomes may also be affected, including decreased neonatal reactivity.
Effects of Uterine Fibroids on the Puerperium
- Large or multiple fibroids may impair uterine involution and cause late postpartum hemorrhage due to inadequate contraction.
- Poor lochial drainage or ulceration of submucous fibroids increases infection risk, especially with lower-segment or large fibroids.
Women with fibroids have higher risks of late postpartum hemorrhage and puerperal infection. In severe cases, uncontrolled bleeding or infection may lead to hysterectomy. Close monitoring for prolonged lochia, increased bleeding, lower abdominal pain, or fever is essential, with prompt antibiotic and uterotonic therapy when needed.
Effects of Pregnancy on Uterine Fibroids
Fibroid growth is strongly hormone-dependent, especially on estrogen and progesterone. Pregnancy-related hormonal changes affect fibroids in several ways:
1. Fibroid Enlargement
Increased estrogen and progesterone cause myometrial hypertrophy, tissue edema, and enhanced blood flow, leading to fibroid enlargement, most notably before 16 weeks’ gestation. Approximately 55% of fibroids grow during pregnancy and often shrink postpartum as hormone levels decline.
Growth patterns vary:
- Early pregnancy: about half change noticeably; others remain stable or slightly enlarge.
- Mid-pregnancy: fibroids 2–5.9 cm often grow, while large fibroids 6–11.9 cm may shrink due to reduced hormone receptor density.
- Late pregnancy: most fibroids stabilize or decrease in size.
Larger fibroids may have fewer estrogen receptors, limiting further growth.
2. Fibroid Degeneration
Red degeneration, a benign form, is most common. It results from vascular injury, hemorrhage, and hemolysis within the fibroid, giving it a fleshy red appearance. It typically occurs in late pregnancy or the puerperium, likely related to localized ischemia.
3. Torsion, Incarceration, or Uterine Torsion
These rare complications mainly affect pedunculated subserosal fibroids. Laparotomy may be required if conservative management fails.