Enhanced preovulatory progesterone levels in clomiphene citrate-induced cycles

We measured basal body temperature, cervical mucus, follicular diameter, and serum LH, FSH, 17 beta-estradiol, and progesterone daily in 40 spontaneous ovulatory cycles in 27 infertile women and in 40 clomiphene citrate-induced ovulatory cycles in 31 women. The cervical score was significantly lower and the serum FSH, LH, and 17 beta-estradiol levels were significantly higher during the follicular phase in induced compared with spontaneous cycles. Serum progesterone was significantly higher on the 3 days preceding ovulation and the day of ovulation in the induced cycles. These increased preovulatory serum progesterone levels could contribute to the lower cervical mucus score in the induced compared with spontaneous cycle, whereas their effect on the endometrium is still unclear.