Glujovsky D, Pesce R, Fiszbajn G, Sueldo C, Hart RJ, Ciapponi A. 2010. The Cochrane Collaboration. Published by JohnWiley & Sons, Ltd.

Couples undergo in vitro fertilisation (IVF) after a long period of subfertility, because women have blocked fallopian tubes or severe endometriosis, where the male partner has a reduced semen count, or when pregnancy has not resulted after previous less invasive fertility treatment. Subsequent to an unsuccessful fresh embryo IVF cycle, a frozen-thawed embryo transfer can be performed when frozen embryos are available. Alternatively for women who have ovarian insufficiency (premature menopause), poor ovarian capacity to respond to stimulation, or have had several unsuccessful IVF cycles, oocyte donation is a frequent  treatment option, particularly for older women. Adequate hormonal preparation of the endometrium is of outmost importance in both egg donor and frozen embryo replacement cycles to provide the optimal chances of pregnancy. Many drugs and various modes of administration have been tried by several investigators in order to optimise implantation rates and consequently improve the success rates of the embryo transfer procedures. A total of 22 randomised controlled trials were included in this review. There is insufficient evidence from these trials to be able to identify one particular intervention for endometrial preparation that clearly improves the treatment outcome for women receiving embryo transfers with either frozen embryos or embryos derived from donated oocytes. Better quality studies are needed to more accurately evaluate each treatment.