Within 1 day of the egg being fertilized,
comprehensive changes have already occurred. By day 4 the embryo has
formed what will become the fetus and the placenta (the organ that
permits the absorption of oxygen, nutrients and the release of carbon
dioxide for the fetus during pregnancy). By day 6 the embryo now called
a blastocyst is ready for implantation into the uterus.
Day1
18 hours after insemination or ICSI, a fertilized egg (zygote)
shows 2 pronuclei. Each pronucleus contains one set of chromosomes.
Day 2
The embryo divides to form two distinct cells (blastomeres).
Day 3
The embryo contains 8 blastomeres and can be transferred back into
the uterus at this stage.
Day 4
Compacting morula: The cells have started to form gap-junctions in
preparation for differentiation into inner cell mass (baby) and
trophectoderm (placenta).
Day 5
- 6
The embryo forms a blastocyst with distinct inner cell mass and
trophectoderm.
A hatching embryo - the blastocyst expands and the
embryo hatches from its shell. Implantation will soon follow.
