Does pregnancy increase fibroid growth?

This study examined whether early pregnancy is a time of increased fibroid growth.

Fibroids, or myomas, are non-cancerous growths that can occur inside or attached to the uterus. It is not clear what causes fibroids, but hormones, such as estrogen, are thought to play a role in their growth. It is unclear whether or not pregnancy, and the hormonal changes it causes, can lead to an increase in fibroid size. Studies have shown inconsistent results, possibly due to different study designs and timing of ultrasounds (a type of imaging that uses sound waves). The current study followed women with fibroids undergoing in vitro fertilization (IVF; an assisted reproductive technique in which an egg is fertilized outside of the body and then implanted in the uterus) to determine whether early pregnancy causes increased growth of fibroids.

This study followed 50 women undergoing IVF: 25 women who achieved pregnancy in a cycle and 25 women who did not. The numbers of fibroids were approximately equal between the two groups (46 in the group who achieved pregnancy and 41 in the group that did not), and no patient had more than four fibroids. Fibroid size was measured prior to the start of IVF and again 5 weeks after embryo transfer (when the embryo is placed in the uterus, after which it will either implant and a pregnancy will start, or will not implant).

There was a significant increase in fibroid size in pregnant women. There was an average diameter increase of 34% in pregnant women, compared to 2% in non-pregnant women. Fibroid volume (the amount of space taken up by the fibroid) increased by an average of 140% in pregnant women and 0% in non-pregnant women. There was no correlation between the drugs used to stimulate ovulation and fibroid growth.

The authors of this study suggested that fibroids grow rapidly in early pregnancy.

This study examined women undergoing IVF treatment, and while they did not find a correlation between ovarian stimulation and fibroid growth, it is not clear from this study whether fibroid growth would be similar in unassisted pregnancies.