Question

At what time does the 4-cell stage occur after fertilisation?

Options

• ~30 hours

• ~72 hours

• ~5 days

• ~60 hours

Answer 1

The 4-cell stage occurs at approximately 60 hours after fertilisation. This represents the second cleavage where each of the two blastomeres divides. The embryo is still enclosed in the zona pellucida and continues its journey through the fallopian tube.