Implantation After Embryo Transfer

The widespread clinical application of in vitro fertilization (IVF) and other advanced techniques of assisted conception has emphasized the relative inefficiency of human reproduction. Currently, only 10%–15% of in vitro-fertilized oocytes implant following transfer into a “synchronous” endometrium. This figure is still well below 20%, even when adverse factors associated with superovulation are negated by transfer of frozen-thawed embryos during natural or hormone replacement cycles. Making some fundamental assumptions regarding the frequency of unprotected intercourse and in vivo fertilization rates, it has been estimated that 25%–30% of naturally created embryos implant [1]. So it would seem that, at present, assisted conception techniques can only match nature when three or more embryos are transferred. A failure to achieve pregnancy in both natural and IVF cycles can be attributed to embryonic factors, endometrial factors or a combination of both.