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ABSTRACT & COMMENTARY
By John C. Hobbins, MD
Professor, Department of Obstetrics and Gynecology, University of Colorado School of Medicine, Aurora
Dr. Hobbins reports no financial relationships relevant to this field of study.
Synopsis: A recent study in patients with fibroids has correlated the size, location, and number of fibroids with the rate of preterm birth, postpartum hemorrhage, need for cesarean section, and fetal size — findings that can be useful in counselling patients with fibroids.
Source: Lam SJ, et al. The impact of fibroid characteristics on pregnancy outcome. Am J Obstet Gynecol 2014;211:395.e1-5.
It is not easy to counsel patients with fibroids about what to expect when they become pregnant or even, more commonly, when fibroids are found for the first time during their pregnancies. The difficulty stems from misleading and/or conflicting data in the literature regarding complications and perinatal outcomes in this setting.
Lam et al reviewed data over a 10-year period in patients with fibroids whose size was ≤ 4 cm.1 During that time, data were available on 121 patients with 179 pregnancies, representing 136 live births. Forty percent had a single fibroid. Nineteen percent had fibroids in the lower segment or had fibroids encroaching on the cervix.
Those women with multiple fibroids had a greater risk of preterm birth (PTB) than women with a single fibroid (18% vs 6%). When fibroids were found in the lower uterine segment, cesarean section was required more frequently (86% vs 40%), and total blood loss at the time of delivery was greater (830 mL vs 530 mL). Also, postpartum hemorrhage was greater in those with fibroids in the lower uterus (22% vs 11%). There was a positive relationship between fibroid size and the rate of postpartum hemorrhage, but, interestingly, there was no effect on birth weight. Smaller fibroids (4-7 cm) had less hospital admissions for “fibroid pain” than larger fibroids (> 7 cm) (5% vs 23%). Last, the size and location of the fibroid had no effect on the rate of preterm birth.
In a book published in 2008, I wrote that “fibroids (in pregnancy) are over-rated.”2 However, the take-home messages from this study are that the location of the fibroid does have an effect on the rates of cesarean section, blood loss, and postpartum hemorrhage. The size of the fibroid has an effect on the rates of postpartum hemorrhage and estimated blood loss. Neither location nor size has an effect on the rate of preterm birth, but the presence of multiple fibroids does increase the risk somewhat of preterm birth, with a rate of PTB of 18%.
The overall prevalence of fibroids in pregnancy is under-reported in the literature (1.4% to 2.7%)3 and overestimated in clinical practice — under-reported because fibroids can often go unrecognized with ultrasound when attention is concentrated on the fetus and over-estimated because an ultrasound exam can be misleading in the first and second trimesters by a prolonged, localized, uterine contraction that can masquerade as a fibroid (a “fibroid” that disappears on a later exam). Older women seeking treatment have a prevalence of fibroids between 12% and 25%.4
There is a misconception that fibroids can grow appreciably during pregnancy, thereby warranting heightened surveillance. Actually, the literature suggests that 60-78% of fibroids do not have any significant change in size during pregnancy.5 If there is growth, it happens predominantly in the first trimester. Interestingly, smaller fibroids have a greater tendency to grow than larger ones. Two studies show that most fibroids decrease in size in the third trimester.5,6
In the featured study, the number of patients requiring admission for “fibroid pain” (5% with smaller fibroids and 25% with larger fibroids) was surprisingly high and far exceeds my experience. “Red degeneration” is a term that has been used sometimes to describe the mottled appearance that the fibroid takes on when it outstrips its blood supply — an event that often coincides in time with the onset of pain. Since this type of tissue necrosis can be accompanied by a release of prostaglandins, prostaglandin synthetase inhibitors (e.g., ibuprofen) are often the best approach to combating fibroid pain.
The above Australian study represents one of the largest sample sizes, consisting of data accumulated over a 10-year period. While giving us a rough idea of perinatal outcome and maternal complications according to size, location, and number of fibroids, the lack of controls does not allow risk to be assessed over baseline.
One of the concerns has been that either the fibroid will compete with the blood supply to the fetus or that a placenta implanting over a fibroid would be less able to supply adequate nutrients to the fetus. This study does not completely answer this question, but it did show that the size and location of fibroids had no effect on the birth weight in the overall population of patients with fibroids. The literature is confusing with regard to intrauterine growth restriction and fibroids. One study suggests a slightly higher rate of low birth weight babies in a population of women with fibroids,7 but this study did not account for confounding factors such as maternal age or, more importantly, gestational age at delivery.
Suggestions for management of patients with fibroids in pregnancy: