What hormonal factor may influence the growth of fibroids?

Oral contraceptives play a significant role in influencing the growth of fibroids due to their hormonal content, particularly estrogen and progestin. Fibroids, or uterine leiomyomas, are benign tumors that can be sensitive to hormonal changes, especially fluctuations in estrogen levels. Oral contraceptives regulate these hormone levels by maintaining more consistent estrogen and progesterone levels in the body.

This hormonal regulation can help manage the size of fibroids, as lower estrogen levels are generally associated with a decrease in the growth of these tissues. Conversely, during the natural menstrual cycle, estrogen peaks can lead to an increase in fibroid growth. Thus, the regulated hormonal environment provided by oral contraceptives may prevent fibroids from enlarging or even cause them to shrink.

Considering the other choices, estrogen replacement therapy could potentially exacerbate fibroid growth due to increased estrogen levels, while progesterone treatment can also stimulate fibroids in some cases. Selective estrogen receptor modulators can have varying effects on fibroids depending on the tissues involved, but they are not primary factors in the growth regulation of fibroids compared to the consistent hormonal balance achieved through oral contraceptives.