Ultrasonographical and hormonal description of the normal ovulatory menstrual cycle.

Objective: To describe the changes in uterine volume, endometrial thickness and follicular size during the normal menstrual cycle by use of transvaginal ultrasonography and to correlate these changes with the endocrine events in the same cycle.

Methods: A group of 23 healthy women with normal body mass index and with a history of regular menstruations were monitored with repeated hormonal and vaginal ultrasonographical investigations during the menstrual cycle.

Results: Sixteen of the women fulfilled the hormonal criteria for ovulation. The mean length of the cycles was 28 days (range 25-30 days) with a mean length of the follicular and the luteal phases of 14.4 days (range 12-17 days) and 13.5 days (range 12-16 days), respectively. The estradiol level in serum the day before the peak of the luteinizing hormone varied between 490 and 1710 pmol/l (mean 1087 pmol/l). Ultrasonographically, the most clinically relevant changes were the increase in diameter of the dominant follicle and the growth of the endometrium. At ovulation the dominant follicle had a mean diameter of 21.4 mm (range 17.4-27.0), whereas the endometrium had a mean thickness of 12.8 mm (range 10.0-15.9). When analysed over the entire follicular phase, the serum estradiol concentration correlated both with the diameter of the dominant follicle (r = 0.93, p = 0.0001) and with the thickness of the endometrium (r = 0.79, p = 0.0001). However, no such correlations were found when only the last part of the follicular phase was analysed. In the luteal phase there was no correlation between the size of the corpus luteum and the serum concentration of progesterone.

Conclusions: Vaginal ultrasonography is a practical and reliable method to monitor structural changes in the ovaries and the uterus during the menstrual cycle. The results are of clinical importance for a better understanding of the physiological changes and helpful when monitoring induction of ovulation in assisted reproduction.