Fibroids in Pregnancy

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2876319/Management of Fibroids in Pregnancy
Uterine fibroids are a very common finding in women of reproductive age.
 The majority of fibroids do not change their size during pregnancy, but one-third may grow in the first trimester. Although the data are conflicting and most women with fibroids have uneventful pregnancies, the weight of evidence in the literature suggests that uterine fibroids are associated with an increased rate of spontaneous miscarriage, preterm labor, placenta abruption, malpresentation, labor dystocia, cesarean delivery, and postpartum hemorrhage.

Fibroids (leiomyomas) are benign smooth muscle cell tumors of the uterus. Although they are extremely common, with an overall incidence of 40% to 60% by age 35 and 70% to 80% by age 50, the precise etiology of uterine fibroids remains unclear.¹
Only 42% of large fibroids (> 5 cm) and 12.5% of smaller fibroids (3–5 cm) can be diagnosed on physical examination.

Early Pregnancy

Miscarriage. Spontaneous miscarriage rates are greatly increased in pregnant women with fibroids compared with control subjects without fibroids (14% vs 7.6%, respectively).¹⁴ The weight of evidence in the literature suggests that the size of the fibroid does not affect the rate of miscarriage, but multiple fibroids may increase the miscarriage rate compared with the presence of a single fibroid only (23.6% vs 8.0%).¹⁴ The location of the fibroid may also be important. Early miscarriage is more common in women with fibroids located in the uterine corpus (body) than in the lower uterine segment¹⁰ and in women with intramural or submucosal fibroids.^7,15–17 The mechanism by which fibroids cause spontaneous abortion is unclear. Increased uterine irritability and contractility, the compressive effect of fibroids, and compromise to the blood supply of the developing placenta and fetus have all been implicated.¹⁸

Bleeding in early pregnancy. The location of the fibroid determines the risk for bleeding. Bleeding in early pregnancy is significantly more common if the placenta implants close to the fibroid compared with pregnancies in which there is no contact between the placenta and fibroid (60% vs 9%, respectively).^2,19

Late Pregnancy

 

Preterm labor and preterm premature rupture of membranes. Pregnant women with fibroids are significantly more likely to develop preterm labor and to deliver preterm than women without fibroids (16.1% vs 8.7% and 16% vs 10.8%, respectively; Table 1).⁷ Multiple fibroids and fibroids contacting the placenta appear to be independent risk factors for preterm labor.^10,19 In contrast, fibroids do not appear to be a risk factor for preterm premature rupture of membranes (PPROM). Indeed, a recent systematic review suggests that fibroids are associated with a decreased risk of PPROM

Placental abruption. Although reports are conflicting, pooled cumulative data suggest that the risk of placental abruption is increased 3-fold in women with fibroids (Table 1).⁷ Submucosal fibroids, retroplacental fibroids, and fibroid volumes > 200 cm³ are independent risk factors for placental abruption.²⁰ One retrospective study reported placental abruption in 57% of women with retroplacental fibroids in contrast with 2.5% of women with fibroids located in alternate sites.³ One possible mechanism of placental abruption may be diminished blood flow to the fibroid and the adjacent tissues which results in partial ischemia and decidual necrosis in the placental tissues overlaying the leiomyoma.³

Placenta previa. The relationship between fibroids and placenta previa has been examined in only 2 studies, both of which suggest that the presence of fibroids is associated with a 2-fold increased risk of placenta previa even after adjusting for prior surgeries such as cesarean section or myomectomy (Table 1).^4,7,21

Fetal growth restriction and fetal anomalies. Fetal growth does not appear to be affected by the presence of uterine fibroids. Although cumulative data and a population-based study suggested that women with fibroids are at slightly increased risk of delivering a growth-restricted infant, these results were not adjusted for maternal age or gestational age (Table 1).^7,22 Rarely, large fibroids can compress and distort the intrauterine cavity leading to fetal deformities. A number of fetal anomalies have been reported in women with large submucosal fibroids, including dolichocephaly (lateral compression of the fetal skull), torticollis (abnormal twisting of the neck), and limb reduction defects.^23–25

Labor and Delivery

Malpresentation, labor dystocia, and cesarean delivery. The risk of fetal malpresentation increases in women with fibroids compared with control subjects (13% vs 4.5%, respectively; Table 1).^7,22 Large fibroids, multiple fibroids, and fibroids in the lower uterine segment have all been reported as independent risk factors for malpresentation.^4,10,21,26

Numerous studies have shown that uterine fibroids are a risk factor for cesarean delivery.^{3,7,10,21,22,27–29} In a systematic review, women with fibroids were at a 3.7-fold increased risk of cesarean delivery (48.8% vs 13.3%, respectively).⁷ This is due in part to an increase in labor dystocia, which is increased 2-fold in pregnant women with fibroids (Table 1).^7,22 Malpresentation, large fibroids, multiple fibroids, submucosal fibroids, and fibroids in the lower uterine segment are considered predisposing factors for cesarean delivery.^{5,10,21,27–29} Despite the increased risk of cesarean, the presence of uterine fibroids-even large fibroids (> 5 cm)-should not be regarded as a contraindication to a trial of labor.^4,21,22

Postpartum hemorrhage. Reports on the association between fibroids and postpartum hemorrhage are conflicting.^{2,10,27,30–32} Pooled cumulative data suggest that postpartum hemorrhage is significantly more likely in women with fibroids compared with control subjects (2.5% vs 1.4%, respectively; Table 1).⁷ Fibroids may distort the uterine architecture and interfere with myometrial contractions leading to uterine atony and postpartum hemorrhage.³³ This same mechanism may also explain why women with fibroids are at increased risk of puerperal hysterectomy.^3,7,20

Retained placenta. One study reported that retained placenta was more common in women with fibroids, but only if the fibroid was located in the lower uterine segment.¹⁰ However, pooled cumulative data suggest that retained placenta is more common in all women with fibroids compared with control subjects, regardless of the location of the fibroid (1.4% vs 0.6%, respectively; Table 1).⁷

 

Uterine rupture after myomectomy. Uterine rupture after abdominal myomectomy is extremely rare.^34–36 In a retrospective study of 120 women delivering at term following abdominal myomectomy in which the uterine cavity was not entered, there were no cases of uterine rupture reported.³⁶ Whether the same is true also of laparoscopic myomectomy is not known, because there are numerous case reports and case series describing intrapartum uterine rupture after laparoscopic myomectomy.^37–45 Recent data suggest that such uterine ruptures occur prior to the onset of labor at the site of the prior laparoscopic myomectomy.^37–39,44 Fortunately, the absolute risk of uterine rupture following laparoscopic myomectomy remains low at 0.5% to 1%.