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Akinrolayo Faith: Inside the IVF Laboratory – Day 2

Photo: DepositPhotos

Aug 24, 2026, 16:28

Akinrolayo Faith: Inside the IVF Laboratory – Day 2

Akinrolayo Faith, Junior Embryologist at Present Help Fertility Clinic, shared on LinkedIn:

“Inside the IVF Laboratory – Day 2

From Zygote to Cleavage-Stage Embryo: What Should We See?

Yesterday, we looked at the fertilization check – particularly the significance of 2PN, 1PN, and 3PN.

But fertilization is only the beginning.

Once the pronuclei disappear, the zygote enters its next major phase: cleavage.

The embryo begins dividing from one cell into multiple cells, without an overall increase in embryo volume.

What are we assessing?

At the cleavage stage, an embryologist isn’t simply counting cells.

We assess several morphological features:

Cell number
Is the embryo developing at an appropriate pace for its developmental day?
Blastomere symmetry
Are the cells relatively similar in size, or is there significant asymmetry?
Fragmentation
How much cytoplasmic fragmentation is present?
Multinucleation
Do individual blastomeres contain more than one nucleus?
Overall embryo organization
Does the embryo demonstrate an appropriate developmental pattern?

Day 2 vs Day 3

A normally developing cleavage-stage embryo commonly progresses from approximately 2-4 cells on Day 2 toward around 6-8 cells on Day 3, although developmental timing can vary.

This is important because embryo development is dynamic.

A single snapshot does not always tell the entire story.

From the embryology bench

One lesson that becomes increasingly important with experience is:

Don’t grade what you expect to see. Grade what you actually observe.

A slower or faster-developing embryo should be assessed based on standardized laboratory criteria rather than assumptions.

And morphology is only one component of embryo assessment.

Research has demonstrated that cleavage-stage morphology can provide useful information about developmental potential, but individual parameters are not perfect predictors of implantation or live birth.

This is why experienced embryologists combine observation + timing + standardized grading + clinical context rather than relying on a single characteristic.