['To determine whether monitoring follicle stimulating hormone (FSH) levels in over-responding patients whom the gonadotropins were withheld would predict pregnancy outcome.', "A group of 33 female infertility patients aged between 20-40 years who had to be coasted during controlled ovarian hyperstimulation were recruited for this study. The FSH concentrations on human chorionic gonadotropin (HCG) day and on the four preceding days were measured to determine the threshold FSH concentration for follicular growth and conception. Mean and standard deviation were used for presenting parametric data. Student's t test and the Mann Whitney U test were used for statistical analysis. Two-tailed P < 0.05 was taken as significant. Receiver-operating characteristic (ROC) curves were performed to identify the cutoff level for FSH and E2 at HCG day and four preceding days.", 'Of 33 cycles, 16 were stimulated with recombinant FSH and 17 with recombinant FSH and human menopausal gonadotropin (HMG). The basal and mean coasting FSH levels of FSH and FSH + HMG cycles did not reveal any differences. FSH concentrations decreased the day after coasting began in 26 cycles and fell by 30.2 +/- 2.7% (range 2-53). In 7 cycles, we observed 34.5 +/- 7.4% (range 6-56) declines in FSH levels beginning 2 days after coasting. Of the 31 women who received HCG, 21 conceived during in vitro fertilization and embryo transfer (IVF-ET). Gestational sac and fetal heart activity were visualized in 14 patients. ROC analysis releaved a cutoff value of 4.9 in FSH level at HCG day discriminative of conception or nonconception.'] Do falling FSH levels predict poor IVF pregnancy rates in patients whom the gonadotropins are withheld?