Effect of bromocriptine on menstrual cycle length.

Forty-seven women with regular ovulatory menstrual cycles and normal plasma prolactin levels were treated with different doses of bromocriptine, and changes in follicular and luteal phase length determined by daily estimation of plasma gonadotrophin concentration. Follicular phase length was highly significantly reduced from a median duration of 12.7 days in the basal cycle to 11.7 days in the first treatment cycle, and to 10.7 days during the second treatment cycles. The length of the luteal phase was unaltered by treatment with bromocriptine. Reduction of follicular phase length was not influenced by the dose of bromocriptine used, and it is concluded that this effect is a consequence of the reduction of plasma prolactin concentration.