MODULATION OF UTERINE ARTERY RESISTANCE TO BLOOD-FLOW BY THE ORAL-CONTRACEPTIVE PILL

The changes in uterine artery resistance to blood flow were studied du ring a normal ovulatory cycle (control) and during a cycle on the comb ined oral contraceptive pill in 10 healthy women, aged 18-35 years, us ing transvaginal color Doppler imaging. Ovulation was monitored using ultrasound and hormonal assays during both cycles. The Pulsatility Ind ex (PI) was used as a measure of uterine artery resistance, on days 8 (midproliferative) and 22 (midluteal) of the control cycle and on days 22 (maximal ovarian suppression) and 28 (minimal ovarian suppression) of the pill cycle. During the pill cycle, the uterine artery resistan ce decreased from a mean PI = 4.37 (range 2.4-7.95) on day 22 to a mea n of 2.79 (1.94-4.99) on day 28, p = 0.006. The uterine artery resista nce was significantly higher on day 22 during the pill cycle compared to the same day of the control cycle, p < 0.0001. Anovulatory cycles o n the oral contraceptive pill are associated with an increase in uteri ne artery resistance and a decrease in uterine perfusion, this effect being reversed during the pill-free week.