Embryo Freezing. Vitrification. Embryo Transfer
Embryo cryopreservation – is a safe method of freezing and storage of embryos in liquid nitrogen by the temperature -196C. Using of such low temperatures allows to stop all the chemical processes in the cells for quite a long period of time. Later these embryos might be successfully defreezed and transferred for the same patient if she hasn’t got pregnant after the IVF cycle or she wants to have one more child. In such cases, there is no need of ovarian stimulation and puncture again. Despite the fact that freezing followed with further unfreezing slightly decreases viability of embryos, possibility of pregnancy is still very high. On the other hand, embryo cryopreservation doesn’t have a harmful influence of the child’s health.
Fertility specialists suggest to use embryo cryopreservation while:
- surrogacy programs;
- getting more embryos of good quality for the next IVF attempts;
- any disease states during IVF cycle (e.g. virus diseases, ovarian hyperstumilation syndrome, emergency operation etc) which significantly decrease chances for conception. That’s why, embryos might be transferred later.
How is embryo cryopreservation conducted?
Embryo cryopreservation is conducted only with normal embryos of high quality and at the strictly defined terms of pregnancy. Embryos with bad indications are never freezed as it causes degradation – destruction of embryos. Stage of development is very important for embryo cryopreservation. Embryos are freezed at the stage of zygote, 2,4,8 cells and blastocyst.
Since very beginning of the program, embryos are transferred into the cryoprotective medium with special medicines which protect cells from the injuries. These medicines prevent the development of ice-crystals inside the embryos and, at the same time, helps to preserve cytoplasm of the cells in the “gel-like” state and to renew its functions later. Then embryos are put into micro-container – plastic tubes (for 4-5 items) with individual markers which are put into cryobank and cooled.
Embryo freezing might be slow or ultraspeed (vitrification). Freezed embryos might be stored for few months or even several years. While unfreezing, tubes are taken from liquid nitrogen and thawed by the room temperature. From the cryoprotector embryos are transferred into special favourable medium. Time of the transfer depends on the stage embryos were freezed. Blastocysts and crushing embryos should be transferred into patient’s uterus at the same day. Less mature embryos should be, first of all, examined and controlled for few days.
Transfer of cryopreserved embryos might be conducted in natural and stimulated cycles or cycle with substitutive therapy. Choice of cryo-protocols depends on the spouses’ reproductive problems.
At the end of the terms of cryopreservation each couple have to decide what to do with their embryos: utilize or store them longer, use for IVF cycle or donate them for other infertile couple, transfer into another clinic or allow their scientific researches.
Embryos after cryopreservation and unfreezing
Not all embryos keep their property after cryopreservation and unfreezing. Percentage of embryo “survival” is usually 75-80% but it much depends on the rate of a medical center and professionalism of the fertility specialists. Embryos are damaged as the result of cryopreservation. In other words, not during their storage but while freezing and unfreezing. That’s why, there might be a necessity to unfreeze few embryos to get 2-3 proper embryos for their transfer into the uterus.