Among ongoing pregnancies with fetal heart activity , the multiple gestation rate with letrozole ( 9 of 67 pregnancies , 13 % ) did not differ significantly from the rate with gonadotropin or clomiphene ( 42 of 192 , 22 % ; P = 0.15 ) or clomiphene alone ( 8 of 85 , 9 % ; P = 0.44 ) but was lower than the rate with gonadotropin alone ( 34 of 107 , 32 % ; P = 0.006 ) .