The effect of timing of embryonic progression on chromosomal abnormality.

Objective: To evaluate the relationship between aneuploidy and timing of blastocyst formation.

Design: Historical cohort study.

Setting: Private IVF clinic.

Patient(s): Ninety-four couples undergoing IVF treatment in combination with chromosomal screening of embryos. The mean maternal age was 39.2 years and average number of embryos per patient 5.3.

Intervention(s): A total of 530 embryos were biopsied on day 3 and underwent chromosome screening with microarray-based comparative genomic hybridization.

Main Outcome Measure(s): Effect of day of embryo blastulation and morphologic grade on aneuploidy rate.

Result(s): Day 5 morulas that progressed to blastocysts on day 6 were significantly less likely to be aneuploid (79.8%) than day 5 morulas that did not progress to blastocysts (92.9%). However, there was no significant difference in aneuploidy rates when embryos that became blastocysts on day 5 were directly compared with embryos that became blastocysts on day 6.

Conclusion(s): Delayed blastulation is not associated with increased aneuploidy rates, but absence of blastulation is associated with increased aneuploidy. Therefore, we conclude that when choosing a morula for transfer on day 5, there may be a benefit in waiting an extra day for the possibility of blastulation to occur.