Multiple gestation is associated with the use of high sperm numbers in the intrauterine insemination specimen in women undergoing gonadotropin stimulation.

Over a 27-month period, the authors observed 70 pregnancies in 66 women following intrauterine insemination (IUI) in conjunction with human menopausal gonadotropins/human chorionic gonadotropin (hMG/hCG) stimulation. Excluding ectopic pregnancies (n = 3) and spontaneous miscarriages (n = 15) during the first 10 weeks of gestation, 14 of the 52 pregnancies (27%) included multiple fetuses: nine twins, four triplets, and one quadruplet. Analysis of patient characteristics and clinical management, as well as semen characteristics of the conception cycle, revealed a significant correlation between gestation type (multiple versus singleton) and the total number of motile sperm in the IUI inseminate (P less than 0.01, Fisher's exact test). General linear models procedures did not identify additional significant relationships between various combinations of parameters examined and the gestation type. The authors conclude that IUI with high numbers of motile sperm constitutes a risk factor in the genesis of multiple gestation. The risk of multiple gestation rises significantly when the inseminate contains more than 20 million motile sperm.