Blastocyst transfer in day-5 embryo transfer depends primarily on the number of oocytes retrieved and not on age.

OBJECTIVE: To analyze the effects of patient age and treatment cycle number on the occurrence of blastocyst transfer and subsequent implantation.
DESIGN: Prospective study.
SETTING: Department of endocrinology and reproduction. PATIENT(S): All 1,099 women had day-5 transfers after IVF or intracytoplasmic sperm injection treatment. INTERVENTION(S): All patients were checked for embryo development in vitro in consecutive day-5 transfer cycles. Two blastocysts or three lesser-developed embryos were transferred. MAIN OUTCOME MEASURE(S): Blastocyst formation rate or clinical pregnancy/implantation rate. RESULT(S): Of 929 patients in the first cycle, 545 (59%) had at least one blastocyst available for ET. Among 151 patients with a blastocyst in cycle 1, 77 developed one or more blastocysts in cycle 2 (51%). Fifty of 143 patients without a blastocyst in cycle 1 had at least one blastocyst in cycle 2 (35%). After subdivision of all day-5 ETs according to the first four cycles, the following implantation rates per embryo were found for ET with one or more blastocysts: cycle 1 (n = 545), 23%; cycle 2 (n = 264), 23%; cycle 3 (n = 110), 14%; and cycle 4 (n = 27), 12%, and with noncavitating embryos, respectively: (n = 384) 6%, (n = 193) 6%, (n = 94) 2%, and (n = 35) 3%. The negative correlation of the age of the woman on blastulation depended primarily on the number of oocytes retrieved. CONCLUSION(S): The blastocyst implantation rate decreased after cycle 2. Biologic ovarian age, rather than chronologic age, determines the frequency of blastocyst transfer or pregnancy rate.