During pregnancy, fibroids can cause problems in some patients, depending on the size and location of the fibroids. As these benign tumors are dependent on estrogen to grow, the high levels of estrogen during pregnancy can, in some cases, lead to rapid growth. If the fibroid is on the outer surface of the uterus, it may present only minor problems, if any, with conception and carrying the pregnancy. If the fibroid is located within the uterus muscle wall or nearer the uterine cavity where the fetus is growing, a patient may be at higher risk for miscarriage. In rare cases, the fibroid may grow so rapidly during pregnancy that it outgrows its blood supply and the center of the tumor undergoes a process of degeneration, which can be painful. Also uncommon, some fibroids may block the lower portion of the uterus and not allow the baby’s head to descend for birth. Cesarean delivery may be necessary in this case.

Fertility and Fibroids

The exact mechanism by which fibroids may prevent embryo implantation is unclear, but it does appear that fibroids that enlarge or distort the uterine cavity do diminish the chances that an embryo will implant in the uterine lining. Fibroids that not distort the lining, do not appear in most cases to cause implantation failure.

Data from a large study by Buttram and colleagues reported that of over 1,200 women undergoing myomectomy surgery for fibroid tumors, 27 percent complained of infertility and 3 percent had a history of miscarriage, but of these women, only 76 women had no other cause for their infertility. When these women underwent myomectomy to remove the fibroids, the conception rate was significantly improved and 40 percent of the women conceived, suggesting but not proving that the fibroids contributed to their infertility. Other more recent studies have reported pregnancy rates in the range of 35 to 60 percent following either abdominally or hysteroscopic (trans-vaginal) myomectomy.

As with any potential fertility factor, the age of the woman must be considered when evaluating results from myomectomy studies. For instance, Buttram’s study reported decreased pregnancy rates following myomectomy when the patients were 36 years old or older. Likewise, the size of the uterus prior to surgery may predict the likelihood of success of the procedure. Women with very large fibroids and with uterine measurements greater than the size of a three-month pregnant uterus had a diminished chance of successful conception after myomectomy.

Location of the fibroid and impact of the fibroid (or fibroids) on the uterine cavity appear to be important factors. A 1995 study by Farhi and colleagues suggested that when the fibroid distorts the endometrial (uterine) lining, the chance that any one embryo will implant at the time of in vitro fertilization was reduced to about one third the implantation rate seen when women had fibroids that did not distort the cavity. In this group of women with non-distorting fibroids, the embryo implantation rate was the same as the women who were undergoing in vitro fertilization with no fibroids present.

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Categories: Fibroids, Myomectomy