INCREASED LEVELS AND PULSATILITY OF FOLLICLE-STIMULATING-HORMONE IN MOTHERS OF HEREDITARY DIZYGOTIC TWINS

According to the endocrine model of hereditary dizygotic twinning, hig h FSH is responsible for multiple ovulation and pregnancy. Our study e xplored the underlying neuroendocrine causes. In a prospective clinica l study, we compared the third day of menses parameters of episodic se cretion of LH and FSH, the pituitary response to LHRH, plasma estradio l, and dimeric inhibin A and B in 16 regularly menstruating and 9 post menopausal mothers of dizygotic twins with a family history of twinnin g and 14 premenopausal and 9 postmenopausal controls. Seven of 16 prem enopausal mothers of twins had abnormally high FSH levels of more than 10 IU/L compared with 1/14 in controls (P = 0.024). In the premenopau sal mothers of twins, mean FSH concentrations (P = 0.025) and FSH puls e frequency (P = 0.003) were significantly elevated, whereas FSH pulse amplitude and FSH response to LHRH were unaltered. For LH, neither th e secretory parameters nor the response to LHRH was different. There w ere no differences between estradiol and inhibin A and B levels. Postm enopausal mothers of twin and controls did not differ with respect to the secretory pattern of LH and FSH. We Conclude that under equal ovar ian feedback conditions, premenopausal mothers of a dizygotic twin hav e hyper stimulation by endogenous FSH caused by neuroendocrine, hypoth alamic, or pituitary mechanisms. This is the result of altered respons iveness to ovarian feedback and/or pituitary or suprapituitary, non-LH RH-like mechanisms that stimulate pulsatile FSH.