Timing of onset of contraceptive effectiveness in Depo-Provera users. II. Effects on ovarian function

Abstract

Objective: To determine the timing of onset of contraceptive effectiveness after the first injection of 150 mg of depot medroxyprogesterone acetate (DMPA) administered between days 8 and 13 of the menstrual cycle.

Design: Descriptive, prospective study.

Setting: A tertiary university referral center.

Patient(s): Thirty healthy women between 18 and 40 years of age.

Intervention: Volunteers were injected with DMPA between days 8 and 13 (5 women on each day) of the menstrual cycle.

Main outcome measure(s): Ovarian function determined by serum levels of E2 and progesterone and follicular development evaluated by vaginal ultrasound.

Result(s): In nine (30%) of 30 women studied, DMPA did not prevent ovulation. All ovulations occurred in women receiving DMPA between days 10 and 13 of the cycle. No woman who received injections on day 8 or 9 ovulated. Ovulation suppression was more effective in women with low ovarian activity. All ovulation occurred within 3 days after the injection.

Conclusion: A back-up contraceptive method, used after the 7th day of the menstrual cycle, is recommended for up to 7 days after the first injection of DMPA.

PIP: To ensure ovulation does not occur, it is recommended that Depo-Provera injections be administered within the first 7 days of the menstrual cycle. In some settings, this requirement acts as a barrier to women's free access to injectable contraception. Thus, the present study investigated the timing of onset of contraceptive effectiveness when the first injection of depot medroxyprogesterone acetate is administered between days 8-13 of the menstrual cycle. 30 women 18-40 years of age attending a university referral center in Campinas, Brazil, in 1995-96, were enrolled. Ovulation, detected through serum progesterone and estradiol assays and confirmed by follicle rupture at vaginal ultrasound, occurred in 9 cases (30%). No ovulations occurred when injection was administered on day 8 (n = 5) or day 9 (n = 5) of the menstrual cycle; only 1 of the 5 women treated on day 10 ovulated. On the other hand, 4 of the 10 women treated on days 11 and 12 and 4 of the 5 injected on day 13 showed evidence of ovulation. All ovulation occurred within 3 days after injection. Ovulation occurred only among women who had serum estradiol levels of 100 pg/ml and above and a leading follicle diameter greater than 13 mm at the time of injection. Ovulation suppression was more effective in women with low ovarian activity. A back-up contraceptive method used for 4 days after Depo-Provera injection should provide sufficient protection when the method is administered after day 7 of the menstrual cycle. However, given the uncertainty of the assumption of short viability of the human oocyte, it is safer to recommend 1 week's use of a back-up method or abstinence.