The standard treatment for women with unexplained infertility is gonadotropins or clomiphene; ovarian stimulation with letrozole has been suggested to maintain birth rates while reducing multiple pregnancies, according to a study published in the New England Journal of Medicine (NEJM). This multicenter randomized trial enrolled couples with unexplained infertility. 18- to 40-year-old women who ovulated and had at least one reopened fallopian tube were randomly assigned to the ovarian stimulation (up to four cycles) group with gonadotropins (301 women), the clomiphene group (300 women), or the letrozole group (299 women). As a result, the incidence of clinical pregnancy after clinical treatment with gonadotropins, clomiphene, or letrozole was 35.5%, 28.3%, and 22.4%, respectively, and the birth rate was 32.2%, 23.3%, and 18.7%, respectively; the pregnancy rate with letrozole was lower than with standard treatment (gonadotropins or clomiphene) or gonadotropins alone, but not lower than with clomiphene alone. The pregnancy rate with letrozole is lower than with standard therapy (gonadotropins or clomiphene) or gonadotropins alone, but not with clomiphene alone. In pregnancies with fetal heart activity, the rate of multiple pregnancies with letrozole (13%) was not significantly different from that with gonadotropin or clomiphene (22%) or clomiphene alone (9%), but was lower than that with gonadotropin alone (32%). All multiple pregnancies in the clomiphene and letrozole groups were twins, whereas gonadotropin treatment resulted in 24 twin pregnancies and 10 triplet pregnancies. The frequency of congenital anomalies or major fetal and neonatal complications did not differ significantly between groups. http://www.dxy.cn/bbs/topic/31983019?keywords=不孕不育