Endocrine and biological factors influencing implantation of human embryos following cryopreservation

Several parameters affecting survival and implantation of frozen-thawed embryos were studied. Of 386 embryos frozen in dimethylsulfoxide (DMSO) or in 1, 2 propandiol (PROH), the survival rate was 63.5% (245/386). Three different methods of cycle preparation were compared prior to thawed embryo replacement. The pregnancy rate was 16.1% (5/56) in spontaneous cycles; 11.4% (5/44) in an ovarian stimulation protocol; and 9.5% (4/42) with estrogen and progesterone substitutional therapy (p = NS). There was no difference in the estradiol/progesterone ratio among the three different protocols during the early luteal phase of the cycle, which may indicate that implantation of thawed embryos could be related to their developmental potential rather than to the endometrial environment. In the spontaneous cycles, when endometrium was synchronized or advanced to embryonic stage up to 32h, implantation rate was 29.2%