#60 : Is the Imbalance of Gender Ratio (GR) in IVF/ICSI Cycles Being Affected by the Current Blastocyst Selection Criteria?

Background and Aims: Studies have reported a GR skewed towards male offspring in the assisted reproductive technology (ART) field due to the current blastocyst selection criteria. Male blastocysts have been observed to develop faster and with better grading than female blastocysts. Thus, more male blastocysts are chosen for being transferred. However, the underlying mechanism to cause the GR shift is still controversial. This study is aimed to investigate the preconception factors which may affect gender distribution.

Method: In this single-centered retrospective cohort study from 2020 to 2022, a total of 1100 (Day 5: 439, Day 6: 661) blastocysts were biopsied. Blastocyst gender and chromosomal abnormalities were identified using next-generation sequencing-based pre-implantation genetic testing for aneuploidy. Blastocysts were categorized into: euploid, mosaic (25-80% mosaicism) and aneuploid. Pearson chi-square test was performed to analyze the GR and ploidy status between the genders.

Results: Overall, the gender distribution skewed significantly towards female (54% vs 46%, p<0.05). However, male blastocysts possessed higher euploid rate than female blastocysts (39% vs 33%, p<0.05). No significant difference was shown in mosaic and aneuploidy rate between males and females (33% vs 36%, 28% vs 31%, p>0.05). Furthermore, the male-to-female ratio was not significant between day 5 and 6 blastocysts (1:1.23 vs 1:1.74, p>0.05), indicating a similar developmental speed between the genders.

Conclusion: Among all the blastocysts analyzed, the GR is biased towards females, but higher euploid rate was observed in male than female blastocysts. Therefore, our results indicate that the imbalanced GR in favor of male offspring using ART may be correlated to the chromosomal issue, rather than blastocyst selection criteria. However, studies on intrapartum factors are necessary to further investigate the underlying mechanism to cause gender shift in ART.