It is known that Clomiphene citrate (CC) reduces endometrial thickness, but it is unknown if additional gonadotrophin stimulation increases endometrial thickness and if this has an effect on implantation rate in in vitro fertilization (IVF). The retrospective study included 263 minimal stimulation IVF-cycles stimulated with 25 mg CC per day (CC- IVF), and 161 IVF-cycles stimulated with CC plus 75IU hMG (human Menopausal Gonadotrophin) per day (CC/ hMG-IVF). Endometrial and oestradiol (E2) measurements were analysed between day -4 and 0 (0 = day of oocyte retrieval) and the association of endometrial thickness and treatment on implantation rates were studied after multiple adjustments. It was shown that on day 0, endometrium was significantly thicker in CC/hMG-IVF versus CC-IVF cycles (9.81 ±2.68 versus 9.06 ±2.54 mm, p = 0.005). However, increased endometrial thickness did not have an effect on implantation and live birth rates. In conclusion, gonadotrophins should not be added to low dose CC treated IVF cycles just to increase endometrial thickness as increased endometrial thickness does not increase implantation rate.
