Blastocyst Transfer

A blastocyst is an embryo which develops five to six days following fertilization and is composed of approximately 75-120 cells. The blastocyst hatches from its outer coat, the zona pellucida, on day 6-7 and implants in the uterine lining. Since only the highest quality embryos continue dividing beyond day 3 of fertilization in vitro (in the laboratory), embryos that form blastocysts may have a slightly higher implantation potential. Because each blastocyst has a higher chance of implantation, the maximum number of embryos for transfer in a blastocyst cycle is two, irrespective of the patient's age. Blastocyst transfer appears to be most useful for younger, good prognosis patients (female partner less than 35 with at least six good quality embryos) who cannot carry a twin or greater multiple pregnancy for medical reasons. The transfer of one blastocyst embryo is recommended for these patients to reduce the chance of a twin pregnancy.