Transfer of frozen-thawed blastocysts that underwent quarter laser-assisted hatching at the day 3 cleaving stage before freezing.

OBJECTIVE: To examine the pregnancy potential of frozen-thawed blastocysts that underwent quarter laser-assisted hatching (AH) at the cleaving stage before freezing and to compare clinical and embryo characteristics between the groups that succeeded in and failed to achieve pregnancy.

DESIGN: Prospective observational study.

PATIENT(S): Thirty-four of 112 patients with frozen blastocysts requiring transfer of thawed embryos between January 2000 and December 2001.

SETTING: Assisted reproductive technology unit in a tertiary medical center.

INTERVENTION(S): Embryos of patients undergoing blastocyst transfers routinely underwent quarter AH using a nontouch 1.48-microm diode laser. Blastocysts not transferred were cryopreserved using a six-step freezing protocol with glycerol as the cryoprotectant.

MAIN OUTCOME MEASURE(S): Postthaw embryo survival and zona pellucida (ZP) maintenance, implantation rate, and clinical pregnancy rate per transfer of thawed blastocysts.

RESULT(S): A total of 118 frozen blastocysts was thawed. Of these, 89 (75.4%) embryos survived and were transferred in 35 cycles. Assisted hatching-manipulated ZP tolerated the freeze-thaw procedures without shape distortion in surviving embryos. Eleven (31.4%) clinical pregnancies with 15 intrauterine gestational sacs occurred, for an implantation rate of 16.9%. Those who succeeded in pregnancy tended to have more embryos available before freezing, more original blastocysts of good quality for freezing, and more surviving blastocysts after thawing for transfer than did those who failed to achieve pregnancy.

CONCLUSION(S): An acceptable clinical pregnancy rate was obtained from transfer of thawed blastocysts that underwent laser AH on the ZP at the day 3 cleaving embryo stage in fresh cycles in selected patients. Embryo characteristics before freezing played major roles in determining implantation potential of thawed embryos.