Eggs that have been fertilized by IVF are placed in a culture medium for about three days. At this stage the embryo is referred to as morula. Embryo transfer is done using a flexible catheter. The embryos are placed in the catheter which is passed through the cervix, after which the contents are injected. In vitro cultured embryo transfer is referred to as IVET (in vitro embryo transfer).
Up to the 16 cell stage the embryo is called zigote; henceforth (from 16 to 64 cells) it takes the name of morula (small blackberry, to which the small cluster of cells now resembles). The 16-cell morula is the form in which the embryo arrives in the uterus, approximately three days after fertilization. After the 64-cell phase, the embryo transforms from a full cluster into a mass with a central cystic cavity and is called a blastocyst. It is the blastocyst that implants itself in the wall of the uterus, about a week after fertilization.
Sometimes, the transfer to the usual stage of three days after fertilization does not lead to pregnancy, as the embryo cannot implant itself. An alternative is to culture the embryo for another two or three days, up to the stage of blastocisti. At this point, the embryo has already developed into its two cell types and the chances of achieving pregnancy may be greater.
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- embryo culture and transfer
- assisted fertilization