Uterine Fibroids and Breastfeeding
by Anne Eglash MD, IBCLC, FABM
Uterine fibroids are non-cancerous growths that occur during childbearing years. According to the authors of this week’s CQW, the prevalence of uterine fibroids during pregnancy is not clear, estimated at 0.1-10%, partially because they are harder to identify during pregnancy. They can cause health problems, such as infertility and risk of pregnancy complications. Sometimes they can twist on their own blood supply, causing inflammation and pain.
Uterine fibroids vary as to whether they grow during pregnancy and if they do grow, they tend to grow in the first trimester. Most fibroids will not grow during the second and third trimesters. Many fibroids become smaller after childbirth and several studies have shown that the more pregnancies a woman has, the lower the risk of uterine fibroids.
In this study done at an Italian medical institution, the authors investigated the effect of childbirth and breastfeeding on uterine fibroids.
This is an observational study that identified 213 pregnant women with a pre-pregnancy diagnosis of a uterine fibroid > 1 cm in size. After excluding several individuals due to multiples, miscarriage, and other issues, 157 were in the final cohort. Approximately 28% underwent a cesarean birth, and 9.5% had a preterm birth. At the 6-month follow-up, 67.5% were still breastfeeding.
- The uterine fibroids of the non-breastfeeding mothers grew postpartum, but the fibroids of the breastfeeding mothers didn’t grow.
- Among all mothers, approximately 37% of the fibroids disappeared postpartum, while approximately 17% of fibroids were larger postpartum.
- Women who breastfed were more likely to have stability or regression of their fibroids at 6 mo postpartum, as long as the fibroids were less than 32mm.
- Pre-pregnancy fibroids over 32mm in size were not more likely to regress in size due to breastfeeding.
- Women who delivered via cesarean had more postpartum regression of fibroids.
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The aim of this study was to investigate the effect of childbirth and breastfeeding on uterine fibroids and to identify the factors associated with size variations. This was a monocenter observational study carried on women with a sonographic diagnosis of uterine fibroids from January 2007 to December 2016, with no indication for immediate treatment, and who became pregnant within one year from diagnosis. All patients were re-evaluated six months after delivery. Fibroid diameters were compared between pre-pregnancy period, first, second, third trimester and post-delivery. The rate of “regressed” (growth of diameter <−40%), “unchanged” (growth of diameter between −40% and +40%) or “increased” (growth of diameter >+40%) fibroids at the post-delivery evaluation with respect to the pre-pregnancy state was calculated. One-hundred fifty-seven women were included in the final analysis. At the post-delivery ultrasound, a significant reduction of the fibroid diameter with respect to all previous examinations was observed, and there was no evidence of 67 (37.2%) fibroids. Ongoing breastfeeding was positively associated with an “unchanged” or “regressed” fibroid diameter (adOR 3.23, 95%CI: 1.35–7.70, p < 0.01). Smaller pre-gravidic fibroids were more likely to return to prepregnancy dimensions or to regress, with a cut-off of 32 mm for lactating women and of 26 mm for nonlactating women. In conclusion, fibroids seem to return to pre-pregnancy dimensions or to regress in the post-partum period. This process may be sustained by uterine involution and hormonal variations, with an additional role of breastfeeding.
The authors discuss several possible reasons why fibroids may be smaller postpartum than pre-pregnancy. The short term decreased blood flow to the uterus when the placenta separates, to prevent excessive blood loss, may cause decreased blood flow to the fibroid, resulting in cell death. Uterine remodeling after birth may also cause cell death of the fibroid tissues. Breastfeeding suppresses the ovarian hormones estrogen and progesterone, preventing stimulation of fibroid growth.
Type of birth, either vaginal or cesarean, had no effect on fibroid growth or regression postpartum.