Levels of oxytocin-like activity and progesterone in follicular fluid from in vitro fertilization cycles.

Oxytocin-like immunoreactivity, estradiol, and progesterone were measured in follicular fluid collected during oocyte collection in an in vitro fertilization program in which clomiphene citrate was used to stimulate follicular development. Follicles which yielded morphologically normal embryos after fertilization of the oocyte had oxytocin concentrations ranging from less than 10 to 600 ng/liter. Oxytocin concentrations did not differ between follicles from 12 pregnancy cycles (median, 169; N = 21) and follicles from 12 nonpregnancy cycles (median, 110; N = 18). Oxytocin concentrations were correlated negatively with progesterone concentrations (Spearman's rank correlation coefficient r = -0.50; P = 0.001). In cycles with some follicles having progesterone concentrations less than 10 and some greater than 10 mumol/liter, oxytocin concentrations were higher in the less progestogenic follicles in 15 of 16 cases.