Objective: To compare implantation and pregnancy rates according to the day
of embryo transfer (day 5 or 6 after oocyte retrieval) when transfer was p
ostponed until expanded blastocysts developed.
Design: Retrospective clinical study.
Setting: Private ART center.
Patient(s): One-hundred and eighty-three women undergoing blastocyst-stage
embryo transfer following in vitro fertilization.
Intervention(s): Bipronucleate oocytes were grown for up to 144 hours and s
ubsequently transferred only when at least one embryo attained the expanded
blastocyst stage.
Main Outcome Measure(s): Implantation and pregnancy rates.
Result(s): Blastocysts transferred on day 5 implanted at nearly twice the r
ate of blastocysts transferred on day 6 (36.3% vs. 19.0%). Pregnancy rates
were also almost twice as high among the day 5 transfer patients (59.3% vs.
32.3%). In addition, more blastocysts developed (3.6 vs. 2.4), and more we
re transferred (2.7 vs. 2.3) to the day 5 transfer patients, although the p
roportion of expanded blastocysts among the blastocysts that were transferr
ed was the same for the two groups (91.7% vs. 93.6%).
Conclusion(s): Embryos that develop to the expanded blastocyst stage and ar
e transferred on day 5 after retrieval are approximately twice as likely to
implant compared to those for which expansion and transfer are delayed unt
il day 6. (Fertil Steril(R) 2001;75:1126-30. (C)2001 by American Society fo
r Reproductive Medicine.).