Uterine fibroids are the most common non-cancerous tumors affecting women of childbearing age. While some women with fibroids may have no symptoms, others may experience infertility, bleeding, and/or pain. In many women, fibroids may disappear or decrease in size during pregnancy or in the postpartum period without any additional treatment. Understanding why fibroids naturally shrink during pregnancy may help scientists develop new treatments for women with fibroids who are not pregnant.
To analyze the factors that might help fibroids shrink in pregnancy, researchers Pregnancy and Perinatology Branch studied over 200 women with fibroids who became pregnant. The scientists used ultrasound to measure the fibroids during early pregnancy, and then again between 3 and 6 months after delivery. Researchers gathered information on the participants’ antibiotic use, breastfeeding, and postpartum contraception use, in addition to demographic information and the gestational age of their newborn.
The study (PMID: 21492823) found that:
- In 72% percent of the women, fibroids shrank in size between the early pregnancy and postpartum periods.
- Black, non-Hispanic women were less likely to have fibroid regression.
- Participants using progestin-only birth control methods postpartum had significantly less fibroid regression than those using a combined estrogen-progestin contraceptive or a non-hormonal contraceptive method.
- Neither the method of delivery (cesarean or vaginal birth) nor the gestational age of the infant was associated with fibroid regression.
- Similarly, none of the other factors in the study was associated with changes in fibroid size – including the woman’s age, BMI, characteristics of the fibroids, breastfeeding, smoking, or antibiotics.