Clinical status of human embryo cryopreservation in the United States of America.

This report describes the results with frozen human embryos from 25 member institutions of the Society of Assisted Reproductive Technology with cryopreservation experience before 1989. Two thousand eighty-five patients had a total of 7397 oocytes and pre-implantation embryos frozen. The number of oocytes, zygotes, cleaved embryos, and blastocysts frozen, thawed, transferred, and the resulting number of pregnancies were 463/127/8/0, 2,133/778/540/47, 4,460/1,567/1,089/68, and 341/186/138/3, respectively. The number of embryos transferred per pregnancy and pregnancy rate per transfer for zygotes, cleaved embryos, and blastocysts were 11.5/17.4%, 16.0/12.5%, and 46.0/4.3%, respectively. The average number of frozen-thawed embryos transferred per pregnancy was 15.0 and the average clinical pregnancy rate per transfer was 13.4%. Forty-eight births have resulted in 41 singletons and 7 sets of twins. Of centers reporting frozen-thawed transfers, 54.6% (12/22) have at least one clinical pregnancy and 75.0% (9/12) of centers reporting a pregnancy have at least one birth.