Among ongoing pregnancies with fetal heart activity , the multiple gestation rate with letrozole ( @ of @ pregnancies , @ % ) did not differ significantly from the rate with gonadotropin or clomiphene ( @ of @ , @ % ; P = @ ) or clomiphene alone ( @ of @ , @ % ; P = @ ) but was lower than the rate with gonadotropin alone ( @ of @ , @ % ; P = @ ) .