Clinical experience with ultra-rapid freezing of embryos

A modified ultra-rapid freezing technique was introduced in January 1989 in our clinical in-vitro fertilization freezing programme. Thus, we wish to report our 1 1/2 year experience with ultra-rapid freezing as a simple and inexpensive method of routine cryopreservation. Of 181 frozen-thawed embryos, 110 (61%) survived with 50-100% blastomeres intact, and were used in 91 embryo replacements. Nine clinical pregnancies were established including two sets of twins. There was one miscarriage and one ectopic pregnancy. So far, five patients have delivered six normal, healthy infants and two other pregnancies are normally ongoing, including another twin pregnancy. These results were similar to those obtained by the conventional slow freezing method using propanediol. There is no doubt that there is a marked advantage of ultra-rapid freezing when compared to previous methods in terms of cost and time. We therefore believe that more clinical attention should be given to ultra-rapid freezing and it should become increasingly the method of choice for human embryo freezing in IVF programmes.