Gonadotropin responses to graded GNRF injections in women with prior twin pregnancies.

Fifteen women with prior twin pregnancies and 20 women with prior singleton pregnancies were investigated in the luteal phase of their menstrual cycles. Measurements were made of their basal LH, FSH, estradiol, progesterone, testosterone and dihydrotestosterone levels as well as their LH and FSH responses to serial graded (0.5 microgram, 5.0 micrograms and 50.0 micrograms) intravenous injections of gonadotropin-releasing factor. The women with prior twin pregnancies were heavier and had a higher parity. Their basal serum progesterone and testosterone levels were not different, but they had lower basal serum estradiol levels and higher basal serum dihydrotestosterone levels. No differences were noted between either the basal or the stimulated gonadotropin (LH and FSH) levels. Thus, no identifiable pituitary trophic factors associated with or causing twinning could be identified in the population studied.