Tamoxifen has been reported to be oestrogenic on the lower genital tract. To evaluate its potential positive effect on the endometrium, and consequently early miscarriage and ongoing pregnancy rate, a prospective study was employed in patients for intrauterine insemination who failed to develop an adequate endometrial thickness in a previous ovulatory cycle. Ovarian stimulation was initiated with tamoxifen 40 mg/day from day 3 of the menstrual cycle for 7 days or clomiphene 100 mg/day for 5 days, in combination with 150 IU of human menopausal gonadotrophin on alternate days starting on day 4. Human chorionic gonadotrophin (HCG) was administered when at least one leading follicle was larger than 20 mm. Intrauterine insemination was accomplished 24-36 h after HCG injection and luteal phase supplement was achieved with micronized progesterone 200 mg transvaginally per day. It was found that tamoxifen-treated patients required more stimulation days and used more gonadotrophin, but recruited less follicles larger than 14 mm than clomiphene-treated patients. However, a significantly increased endometrial thickness (P < 0.001) and pregnancy rate (P = 0.015), decreased early miscarriage rate (P = 0.001) and thus improved ongoing pregnancy (P < 0.001) rate were noted in tamoxifen-treated patients. These results suggest that although tamoxifen may not be a first-line treatment in patients with adequate endometrium, it may be a promising alternative for patients with thin endometrium.

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An adequate thickness and pattern of the pre-ovulatory endometrium is considered one of the essential requirements for a successful pregnancy. Although various methods for increasing endometrial thickness have been proposed, the real value of these interventions remains controversial. Here, we present a case of successful administration of extended estrogen supplementation before conventional controlled ovarian hyperstimulation in a woman who had experienced repeated implantation failure because of an unresponsive thin endometrium. After the estrogen supplement was administrated for an extended period, the in vitro fertilization/embryo transfer in this patient led to an uneventful twin pregnancy and delivery at term.