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Khalil Faaed: Osmolality – The Hidden Variable in Embryo Culture

Khalil Faaed/LinkedIn

Aug 29, 2026, 16:43

Khalil Faaed: Osmolality – The Hidden Variable in Embryo Culture

Khalil Faaed, Embryologist at Modern IVF Center, shared on LinkedIn:

”What if your IVF culture medium has the ‘right’ pH and temperature but the osmolality is quietly changing?

We often focus on the variables we can see on the incubator:

Temperature
CO₂
pH

But another physicochemical parameter deserves equal attention:

Osmolality.

Osmolality describes the concentration of osmotically active particles in the culture environment.

For an embryo, this is not simply a laboratory number.

The osmotic environment influences water movement across cell membranes and therefore contributes to cellular volume regulation and embryo physiology.

And here is where IVF laboratory practice becomes particularly important.

Culture-medium osmolality can be influenced by factors such as:

Medium composition
Evaporation
Drop volume
Oil overlay
Time outside controlled conditions
Temperature and environmental stability
Handling and equilibration

Even the physical design of the culture system can matter.

Smaller culture volumes can be more susceptible to changes in osmolality, while appropriate oil overlay and controlled environmental conditions can help reduce fluctuations. Importantly, the optimal osmolality for human embryo culture is not defined by a single universal number; culture systems and media formulations differ.

This leads to an important laboratory principle:

Do not evaluate culture conditions one parameter at a time.

A medium with an acceptable pH may still be experiencing changes in other physicochemical variables.

So when we talk about embryo culture quality, perhaps the better question is not:

Is our pH correct? but:

Is the entire physicochemical environment stable?