Day of egg retrieval

Motile sperm selected by the swim-up procedure for IVF or ICSI.

Day of egg retrieval

Cumulus cells surround this egg that has been aspirated from a mature follicle.

Day 1

The two pronuclei visible in the center of the egg indicates normal fertilization.

Day 2

A normally-progressing embryo will be at the 4-cell stage. The 4th cell is seen slightly above the focal plane in the center of the embryo.

Day 3

A normally-progressing embryo will be at the 8-cell stage, but the cell number can range from 5 to 12 cells.

Day 4

The cells of this Morula-stage embryo are compacting and are not as distinct as they were on Day 3.

Day 5

An embryo will become a blastocyst by forming a fluid-filled cavity. At this stage, the cells differentiate into those destined to become the baby (inner cell mass; seen as a small clump of cells at 7:00), and the placenta and amniotic membranes (trophectoderm; cells on the perimeter).

Day 6

The blastocyst must hatch from the zona pellucida to implant in the uterus. This will occur after the embryo has been transferred into the uterus.