Dynamic changes in ovarian follicles measured by ultrasonography during gonadotropin stimulation in rhesus monkeys

The objective was to study dynamic changes of ovaries in rhesus macaques stimulated by gonadotropins to identify an indicator for predicting ovarian response to stimulation. Twenty-one cycling monkeys were given 36 IU/d recombinant human follicle-stimulating hormone (rhFSH) for 8 d. Animals (n = 17) with ≥5 follicles (≥3 mm) in their ovaries on Day 9 of ovarian stimulation were deemed good responders, whereas those with a lesser response were poor responders (n = 4). For these two groups, the mean (±SD) numbers of oocytes retrieved were 44.3 ± 21.4 and 11.0 ± 4.6, respectively. In retrospect, the mean diameters of the ovaries and of the largest follicles, the total number of detectable follicles (diameter >0.5 mm), and serum estradiol concentrations gradually increased during the stimulation period in the good responders but did not increase in the poor responders. Comparing good and poor responders, the number of ovarian follicles >0.5 mm already exhibited a difference (12.9 ± 6.5 vs. 2.9 ± 1.3, respectively, P < 0.05) on Day 1 of stimulation. However, for other end points, differences were not significant until at least Day 5. Moreover, good responders yielded a fivefold higher blastocyst development rate than that of poor responders (P < 0.01). In conclusion, the number of ovarian follicles detected with ultrasonography could be useful to predict the response to FSH stimulation in non-human primates.