ABSTRACT
Coasting, or delaying hCG, uses a controlled ‘drift’ period as an alternative to cancellation of the cycle, yielding favorable pregnancy rates (25% per cycle) with low severe OHSS complications (2.5%). In one study by Sher et al.29, gonadotropins were withheld in 17 patients whose serum estradiol levels were >6000 pg/ml and daily administration of the GnRH analog was continued until estradiol levels had fallen to <3000 pg/ml. At this point, 10 000 IU hCG were administered to trigger ovulation. During the first 48 h of initial coasting, the estradiol levels continued to rise, but the follicular diameter reduced by approximately 2.3 mm/day. The estradiol levels plateaued and fell after 96 h. No follicular increase in diameter was seen after 72 h of coasting. The coasting period lasted 4-9 days; hCG administration was reduced on days 12-16. Interestingly, 35% of the cycles led to viable pregnancies and all 17 patients developed signs of grade 2-3 OHSS, however none led to severe OHSS. An update review abstract from the Cochrane Library30, however, identified 13 studies (of which only one met the strict inclusion criteria), showing no difference in the incidence of moderate or severe OHSS, or pregnancy rates, between the groups.
