Management of overstimulated gonadotrophin cycles with a controlled drift period

In an attempt to avoid cancellation, 40 cycles which were biochemically overstimulated with exogenous gonadotrophins (oestradiol level inadvertently exceeding 5400 pmol/l) in 32 patients with polycystic ovarian syndrome, classified as Group II according to the World Health Organization, were managed by a controlled drift period. This involved a schedule where further human menopausal gonadotrophin (HMG) injections were withheld but monitoring continued with daily assays of serum oestradiol and frequent follicular ultrasound examinations. The mean oestradiol level at the start of the drift period was 9249 +/- 3465 (SD) pmol/l and dropped by 64.3 +/- 25.3% to 2945 +/- 1817 pmol/l at the end of 2.8 +/- 1.5 days of drift interval (range 1-8 days) at which time human chorionic gonadotrophin was administered. There was a significant increase in the size of the lead follicle and number of follicles greater than 14 mm in diameter during the drift period. The clinical pregnancy rate per cycle was 25% (10/40). The multiple pregnancy rate was 50% (5/10), and 2.5% (1/40) of the cycles were complicated by severe ovarian hyperstimulation syndrome (OHSS). These data indicate that cycles inadvertently overstimulated with gonadotrophin can be managed with a controlled drift period as an alternative to cancellation, yielding favourable pregnancy rates. The multiple pregnancy rate was 50%, twins in all instances and the rate of severe OHSS was 2.5%, which were within the range reported in the literature for HMG-stimulated cycles.