ABSTRACT
Depo-medroxyprogesterone acetate (DMPA) in the conventional dose of 150 mg, was administered intramuscularly to 49 healthy, already sterilized, Thai women on cycle day 5 (13 subjects), day 7 (12 subjects), day 9 (13 subjects) and day 11 (11 subjects) of normal menstrual cycles. Serum progesterone levels were then monitored in order to ascertain the latest follicular phase day in the cycle (up to day 11) when ovulation would be inhibited in the first month after injection. Among the 25 subjects who received DMPA on day 5 and 7, no longitudinal serum progesterone level rises indicative of ovulation were detected. When DMPA was given on day 9 and 11, 2 out of 13 subjects (15.39%) and 3 out of 11 subjects (27.28%), respectively, had serum progesterone levels characteristic of ovulation. It is concluded that the initial cycle's ovulation can also be inhibited when DMPA is administered on day 7 of that cycle. However, DMPA administered on day 9 and 11 failed to inhibit ovulation of that cycle in some of the subjects.
