Injections of Lupron, Metrodin, Pergonal or Humegon allow the ovaries to develop many follicles as seen in this ultrasound immediately prior to egg retrieval.

Immediately after fertilization, the egg contains two pronuclei. Each contains half the chromosomal material from each one of the genetic parents.

A four cell pre-embryo. Each of the cells is called a blastomere. The embryo is surrounded by a protein matrix "shell" called the zona pellucida.

On the third day after egg retrieval eight cell pre-embryos can be tranferred to the uterus. On average, 15% of embryos such as this will implant after being transferred.

Prior to implantation, the pre-embryo, now at the blastocyst stage, must hatch out of the zona pellucida prior to implantation.