# Diameter of Human Day Five Blastocysts and Birth Sex

## TL;DR

This study examined if the diameter of day five blastocysts could predict the sex of the baby born after embryo transfer, finding a general tendency toward more female births but no strong link to blastocyst size.

## Contribution

The study explores a potential morphological link between blastocyst diameter and offspring sex in ART procedures.

## Key findings

- More female than male babies were born in the study.
- Blastocysts leading to female offspring tended to be larger, though not statistically significant.
- Fresh embryo transfers showed a tendency for larger blastocyst diameters compared to cryo-thawed transfers.

## Abstract

Background

This study aimed to evaluate the offspring sex ratio, born through fresh and cryo-thawed single blastocyst (BL) transfers regarding a single morphological, static parameter, namely, BL diameter.

Methodology

This retrospective, observational study was conducted at an assisted reproductive technology (ART) center, Kinderwunschzentrum Niederrhein Germany. We conducted a statistical analysis of all births resulting from fresh and thawed in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) cycles after a single embryo transfer (SET). The main outcome measure was the offspring sex ratio after SET of a day five BL in relation to the BL diameter measurement.

Results

There were more female than male babies born in our study. We observed a tendency for BL to have a higher diameter, resulting in female offspring, which was not statistically relevant. We also compared the BL diameter in the fresh embryo transfer (ET) group with that of the cryo-thawed ET group, showing a tendency toward a larger diameter in the fresh ET group. In the ICSI cycles, there was a higher tendency for a larger BL diameter when compared to IVF cycles. In the fresh ET cycles, BL leading to the male sex at birth had a tendency toward a larger diameter than the female BL. In the cryo-thaw ET cycles, BL leading to the female sex had a tendency toward a larger diameter than the male BL.

Conclusions

Our results showed a tendency in the sex of offspring toward the female sex and no significant difference in the BL diameter of BL leading to birth after ART and consecutive transfer of day five BL.