Kate Johnson of the Montreal Bureau contributed to this report.
MONTREAL — Continuous oral contraceptive regimens suppress ovulation better than do conventional 21-day regimens, according to research presented at the conjoint annual meeting of the American Society for Reproductive Medicine and the Canadian Fertility and Andrology Society.
This effect of continuous oral contraceptives (COCs) has not been previously reported, said Roger Pierson, Ph.D., explaining that COCs have been promoted primarily for their ability to eliminate cyclic bleeding and premenstrual symptoms.
“The side effect of not bleeding is much more effective contraceptive control,” said Dr. Pierson, professor of obstetrics, gynecology, and reproductive sciences at the University of Saskatchewan, Saskatoon.
In his single-center, randomized, open-label trial sponsored by the Canadian Institutes of Health Research, Dr. Pierson compared two different formulations of traditional 21-day oral contraceptive (OC) regimens with the same formulations given continuously for 28 days per cycle. Women took the pills for three cycles. Transvaginal ultrasonography was used to monitor follicular development once weekly for the first 3 weeks of the study and then every third day until the end of the third cycle.
The nine women on the 28-day regimen of 30-mcg ethinyl estradiol/150-mcg levonorgestrel and the 11 women on the 28-day regimen of 35-mcg ethinyl estradiol/250-mcg norgestimate showed less follicular development than did the women given the traditional 21-day regimens of both formulations (8 women in each group).
The women on the continuous regimen had no dominant follicles and no ovulations. Together, women on the standard regimens produced a total of eight dominant follicles, two of which ovulated.
The time to return of normal ovulation during the first cycle after contraceptive discontinuation was measured in both the conventional OC and COC groups, and this was compared with historical data for ovulation after discontinuation of other forms of contraception.
Follicles developing after discontinuation of COCs took about 5 days longer to ovulate than did follicles developing after discontinuation of conventional OCs. Time to ovulation for both OC groups was longer than in natural cycles. In addition, serum estradiol 17-? at a follicular diameter of 18 mm was significantly higher after discontinuation of OCs, compared with natural cycles. Dr. Pierson said the delayed return to normal ovulation was not significant, but noted the study's short length.