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Sean Lauber: Does Transferring a Cleavage or Blastocyst Stage Embryo Affect the Chance of Having a Boy?
Sean Lauber/LinkedIn
Jul 25, 2026, 10:38

Sean Lauber: Does Transferring a Cleavage or Blastocyst Stage Embryo Affect the Chance of Having a Boy?

Sean Lauber, Healthcare newsletter writer at SmartBrief, shared a post on LinkedIn:

“Does transferring a cleavage stage or blastocyst stage embryo affect the chance of having a boy?

Perlman et al. (2021) analyzed nearly 100,000 frozen embryo transfers (FETs) from the US SART registry to see whether embryo stage affected the baby’s sex.

Cleavage stage transfers resulted in 50.5% male births, while blastocyst stage transfers resulted in 51.9% male births.

Although the difference was statistically significant, it was small (corresponding to 1.4 additional boys per 100 live births after blastocyst transfer). This isn’t enough to influence embryo selection, but it does suggest that blastocyst transfer is associated with a slightly higher chance of having a boy.

Other studies, including a 2022 meta-analysis, have reported similar findings.

Researchers aren’t sure why this happens. One possibility is that male embryos develop slightly faster than female embryos, making them more likely to reach the blastocyst stage first. Since clinics generally transfer the most advanced embryo first, this could slightly increase the chance of transferring a male embryo. However, the exact reason isn’t clear.

Check out more details on Remembryo

Like this post? Get a free weekly summary of the latest IVF research.”

Sean Lauber: Does Transferring a Cleavage or Blastocyst Stage Embryo Affect the Chance of Having a Boy?

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blastocyst stage blastocyst transfer cleavage stage Fertility Fertility News frozen embryo transfers (FETs) live births male births reproductive health Reproductive Medicine Sean Lauber
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