Uterine Fibroids and Pregnancy

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Uterine fibroids are benign (meaning not cancerous) tumors that include leiomyomas (often simply called myomas) that develop in the smooth muscle of the wall of the uterus. Leiomyomas can be present prior to pregnancy, during pregnancy, or after a woman gives birth. As pregnancy develops and advances, however, these tumors can cause trouble, since they occupy space in the uterus and interfere with its normal ability to stretch evenly. Uterine fibroids are the most common tumors in the female pelvis. About 60 percent of reproductive age women and 80 percent of women overall will have uterine fibroids. Uterine fibroids are reported to exist in about 11 percent of pregnancies. Very likely, however, the percentage is higher, since only very large fibroids produce symptoms.

Your doctor will suspect that you have uterine fibroids if you report of uterine bleeding, especially heavy bleeding during your menstrual cycle and if a routine pelvic exam provides the doctor with certain signs. Blood tests also will be ordered to test for hormone levels and signs of blood loss. After this, the presence of uterine fibroids can be confirmed through several techniques, such as hysteroscopy, hysterosonography magnetic resonance imaging (MRI), and hysterosalpingography.

Generally, uterine fibroids do not cause major problems during pregnancy but, when the fibroids grow large, they may cause problems whether or not the woman is pregnant. Regarding the former, the presence of fibroids during pregnancy increases slightly the risk of spontaneous abortion (miscarriage) and preterm delivery, which can lead to some medical problems during infancy and behavioral problems during childhood.

Medications to treat uterine fibroids are hormonal treatments, such as gonadotropin-releasing hormone (Gn-RH) agonists. These treatments block the production of estrogen and progesterone, making it as if you were post-menopausal, so they are not given during pregnancy. Another treatment is an implanted device that releases the hormone progestin. Non-hormonal treatments include tranexamic acid that you take only on days with heavy menstrual bleeding (thus not during pregnancy), oral contraceptives, and nonsteroidal anti-inflammatory drugs (NSAIDs). NSAIDs include ibuprofen, naproxen, and various other agents. Oral contraceptives must not be taken at any point during pregnancy, whereas NSAIDs must be avoided during late pregnancy.

Hormone therapy is avoided for uterine fibroids during pregnancy. The standard treatment for fibroids in this case is simply “watchful waiting”. That’s because most uterine fibroids are small and do not produce symptoms. Furthermore, fibroids can wax and wane over time, and pregnancies generally proceed normally in the presence of uterine fibroids. On the other hand, in severe cases, you can work with your doctors and decide on a range of treatment options, some of which could begin during pregnancy, while the rest could start after you give birth. As for breastfeeding, NSAIDs are considered fairly safe in nursing mothers, while hormonal treatments for uterine fibroids are probably safe, because breast milk tends to be full of sex hormones anyway.

When medical treatment is not enough, there are surgical procedures, including myomectomy (removal of the fibroids), ablation (destroying them with heat, microwaves, electric current, low temperature, or radiofrequency, or by uterine artery embolization –the intentional production of blood clots in the arteries that feed the fibroids.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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