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Updated: Jul 5, 2025

Human Blastocyst Biopsy and Vitrification
Published on: July 26, 2019
Sperm intrusion into the implantation-stage blastocyst and its potential biological significance
Jayasree Sengupta1, Thomas Kroneis2, Amy M Boddy3
1Department of Physiology, All India Institute of Medical Sciences, New Delhi, India.
Abstract:
The human embryo derives from fusion of oocyte and sperm, undergoes growth and differentiation, resulting in a blastocyst. To initiate implantation, the blastocyst hatches from the zona pellucida, allowing access from external inputs. Modelling of uterine sperm distribution indicates that 200-5000 sperm cells may reach the implantation-stage blastocyst following natural coitus. We show ultrastructural evidence of sperm cells intruding into trophectoderm cells of zona-free blastocysts obtained from the uterus of rhesus monkeys. Interaction between additional sperm and zona-free blastocyst could be an evolutionary feature yielding adaptive processes influencing the developmental fate of embryos. This process bears potential implications in pregnancy success, sperm competition and human health.
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