Pathology Portal

Reproductive Science - Clinical Embryology images of human preimplantation embryos - 2-cell embryo

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Following fertilisaton, the two pronuclei (one from the male and one from the female) undergo syngamy. This results in the genetic contributions forming a unique combination for the first time.

The zygote must then undergo the first mitosis and first division. This is a crucial step for the fertilised oocyte. If successful, a two-cell embryo forms. This is usually at the start of the second day of life.

Each cell is now called a blastomere. If the embryo is viable, then each blastomere is diploid.

During IVF treatment, a clinical embryologist assesses each two-cell embryo for shape and symmetry, If both cells are equal-sized, oval and symmetrical, then the embryo is classed as good quality. However, sometimes, the cells are asymmetric and may have formed many smaller fragments of cytoplasm. This indicates a poorer quality embryo that is less likely to implant.

Resource details

Contributed by: Pathology Portal
Authored by: Bryan Woodward, X and Y Fertility, Reproductive Scientist
Catherine Reynolds, NHS Greater Glasgow and Clyde, Reproductive Scientist
Licence: © All rights reserved More information on licences
Last updated: 12 July 2023
First contributed: 15 April 2023
Audience access level: Full user

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