Uterine Leiomyomas and Pregnancy Outcomes
Yes, uterine leiomyomas (fibroids) significantly affect pregnancy outcomes, with the impact heavily dependent on fibroid location and size—submucosal and intramural fibroids increase risks of preterm delivery, placental abruption, and cesarean delivery, while subserosal fibroids have minimal impact on pregnancy outcomes.
Impact on Fetal Growth
The evidence shows that leiomyomas do not typically cause intrauterine growth restriction (IUGR) in term pregnancies 1, 2. When low birth weight occurs in pregnancies complicated by fibroids, it is primarily due to preterm delivery rather than growth restriction 1. One study specifically found that fibroids did not significantly alter the incidence of intrauterine growth retardation 2.
However, there is a critical exception: retroplacental fibroids (those located beneath the placenta) carry substantially higher risks, with one study showing 57% of patients with retroplacental leiomyomas developed placental abruption, resulting in four fetal deaths 2. This represents a dramatically elevated risk compared to the 2.5% abruption rate when fibroids are not retroplacental.
Impact on Delivery Outcomes
Preterm Delivery Risk
Pregnant women with leiomyomas face significantly increased risks of preterm birth 1, 3:
- 1.7-fold increased risk of delivery before 34 weeks (adjusted OR 1.7,95% CI 1.1-2.6)
- 1.9-fold increased risk before 32 weeks (adjusted OR 1.9,95% CI 1.2-3.2)
- 2.0-fold increased risk before 28 weeks (adjusted OR 2.0,95% CI 1.1-3.8)
The risk of premature labor correlates positively with the size of the largest myoma, occurring in 21.5% of patients with fibroids 2.
Cesarean Delivery
The presence of uterine leiomyomas dramatically increases cesarean delivery rates, with a 6.7-fold increased risk (OR 6.7,95% CI 5.5-8.1) compared to pregnancies without fibroids 3. This elevated rate persists even after adjusting for maternal age, parity, gestational age, and malpresentation.
Other Delivery Complications
Pregnancies with fibroids are associated with 4, 3:
- Placental abruption: 2.6-fold increased risk (OR 2.6,95% CI 1.6-4.2)
- Abnormal fetal presentation in labor
- Pelvic outlet obstruction
- Postpartum hemorrhage
- Puerperal sepsis
Perinatal Mortality
The data on perinatal mortality shows nuanced findings. While crude rates appear elevated (2.2% vs 1.2%), after controlling for confounders including maternal age, parity, and gestational age, the difference in perinatal mortality is not statistically significant (OR 1.4,95% CI 0.7-2.8) 3.
However, intrauterine fetal demise (IUFD) risk is significantly elevated at earlier gestational ages, with a 4.2-fold increased risk before 32 weeks (OR 4.2,95% CI 1.2-14.7), though not after 32 weeks 1.
Location-Specific Effects
The type and location of fibroids critically determine pregnancy outcomes 4, 5:
Submucosal (SM) fibroids: Associated with increased risks of spontaneous abortion, preterm delivery, and significantly reduced implantation rates (4.3% vs 15.7% in controls)
Intramural (IM) fibroids: Even without cavity distortion, these reduce pregnancy rates (16.4% vs 30.1% in controls) and implantation rates (6.4% vs 15.7%)
Subserosal (SS) fibroids: Pregnancy and implantation rates are NOT influenced by subserosal fibroids (34.1% pregnancy rate, comparable to 30.1% in controls) 4
Clinical Management Implications
Women with leiomyomas constitute a high-risk obstetric group requiring specialized management 6, 7:
Preconception counseling should address fibroid characteristics (type, size, location, number) as these determine pregnancy risk stratification 5
Surgical or medical treatment should be considered for intramural and submucosal fibroids before attempting conception, particularly for those undergoing assisted reproductive technology 4
During pregnancy, women with fibroids require closer monitoring, particularly those with:
- Retroplacental fibroids (highest risk for abruption)
- Large fibroids (increased risk of pain requiring narcotics in 15.1% and premature labor in 21.5%)
- Multiple fibroids
Hospitalization in specialized obstetrical facilities is recommended during high-risk pregnancy periods 6
Important Caveats
- Passive surveillance is not advisable for women of childbearing age with uterine leiomyomas 6
- The clinical significance depends heavily on fibroid characteristics—size, position, and number all matter 4, 5, 2
- Most fibroids are asymptomatic and require no intervention 7
- Hysteroscopic myomectomy for submucosal fibroids does not appear to reduce preterm delivery rates or other adverse obstetrical outcomes, though it may improve fertility 8, 9