The growth of the embryo is assessed and at a suitable stage, the embryo is transferred back to the female’s uterus at the four or eight cell stage by means of a fine tube inserted through the cervical canal. The embryo is held between the two air bubbles in a fine tube. More than two embryos are usually transferred to improve the chances of success.
- 2-embryo transfer: 15 % success
- 3-embryo transfer: 25 % success
- 4-embryo transfer: 35 % success
This practice has resulted in many multiple births about 20-25%, compared to just 1 % in the general population. This has raised reasons for concern due to stillbirth, high infant mortality rates and the risk of delivering low birth weight babies.
For each month an attempt is made, only about 10 % eventually end up in a live birth. The major stumbling block in the IVF seems to be the failure of the embryo to implant after transfer to the recipients uterus.