The oocyte retrieval is an ultrasound guided transvaginally puncture of the ovary to get the mature oocytes from the ovarian follicles out. This is done under a mild sedation and local analgesia, and takes no more than 5-10 minutes. Immediately after the egg collection you will know how many eggs are retrieved and their quality. Sometimes you need a short rest after the procedure, but many of our patients go home very soon after the procedure.
The fertilization takes place 1-4 hours after the egg collection. The technician have prepared first the oocytes in a culture medium and the sperm sample has been washed to ensure only living, normal sperm cells are present in the fertilization medium. In case of a very low sperm quality, micro insemination, also called ICSI is used to place a single sperm into the egg. The next day the eggs are checked for fertilization.
At the moment the eggs are fertilized, we call it an embryo. These cleave from 1 cell to 2 cells and hereafter to 4 cells etc. On day 2 of culture we normally see 4 cell embryos. However sometimes no eggs are fertilized. This is seen in 6% of all cases and also only 80% of the fertilized embryos do cleave.
The quality of the eggs and embryos are varying in-between treatment cycles and in-between the individual embryos. The embryologist is using these quality scores to select the best embryos for embryo transfer. Today we are so efficient in selecting the best embryos by using several different selection criteria such as spindle apparatus (see this), cleavage stages, fragments and zona pellucida thickness. This means that very often we prefer to transfer only one embryo and take the rest for freezing to be used in the following cycles if not pregnant.
When the embryo has been selected for transfer, maybe also assisted hatching has been done, the embryo is placed in a small catheter and given to the doctor. He will take the catheter and introduce it into the endometrial cavity. This is uncomfortable but not associated with any pain. The procedure is often followed by transabdominal guided ultrasound.
In some cases, the embryo quality is good enough for freezing. This is then done, and these embryos can be stored here up to 5 years. Either to be used if not pregnant in the next cycle or if the woman gets pregnant in the fresh cycle to be used for the next child.
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