What is embryo freezing / cryopreservation?

Embryo cryopreservation is the process of preserving an embryo obtained from IVF /ICSI procedure that is, from fertilization to cleavage stage(day3) or blastocyst stage(day5) at sub-zero temperature (-196degreeC) using Vitrificationtechnique. Embryo freezing is a great way to preserve your fertility. Vitrification appears to result in decreased risk of DNA damage than any other freezing technique.


Why is embryo freezing done?

Embryo cryopreservation is done

  1. If the woman is responding excessively to the stimulation drugs and she has produced too many eggs, she will be at risk of developing ovarian hyperstimulation syndrome (OHSS) if embryos were transferred in the same cycle.
  2. Endometrial problems: Thin endometrium, endometrial polyp, Fluid in the endometrium, Thick endometrium. These problems will affect the lining of the womb making it less receptive to embryos.
  3. The woman may have other medical condition that requires treatment before transferring the embryos back to the womb.
  4. Asynchrony of the treatment cycle between donor and recipient / surrogate.
  5. Excessive embryos remaining after embryo transfer during IVF treatment, where it could be utilised if failed or for the second pregnancy.
  6. Cryopreservation of the extra embryos to avoid multiple pregnancies.
  7. It allows Preimplantation genetic screening (PGS) that tests looking for chromosomal abnormalities.


How is embryo freezing done?

Embryo obtained out of IVF/ICSI procedure on day3 or day5 of culture are frozen using vitrification technique which is an advanced method.

Embryos are put in embryo containers called storage straws and then frozen by vitrification (rapid freezing). The straws containing the embryos are eventually stored in liquid nitrogen tanks. Water in the cell is replaced by a substance known as cryoprotectant. Embryos are further left to equilibrate in the cryoprotectant increasing levels before the freezing starts. The embryos are frozen in their preservation stage after this.

The cryoprotected embryos freeze in this procedure so quickly that the molecules of water do not get enough time to form crystals of ice. The embryos are protected and their chances of survival increase during thawing.

The vitrification method has a higher embryo survival rate on thawing as compared to the old-fashioned slow freezing method, and has therefore become the preferred method of freezing embryos nowadays.

Is there any chance where the embryos are mixed up?

NO! All Straws or ampoules used for each patient’s embryos are carefully and permanently labeled forlater identification purpose.

Will long storage period have impact on embryo?

The outcome from using long period cryopreserved embryos has uniformly been positive with no increase in birth defects or any other abnormalities.Your chances of becoming pregnant with a thawed frozen embryo are not affected by the length of time the embryo has been stored for.

How long can the embryo be stored?

In India, as per ICMR guidelines, embryos can be frozen for a maximum period of five years. If patient wish to extend this period,they are requested to inform the clinic in prior.

Do the couple / patient need to pay for embryo freezingto extend for certain period of time?

Constant maintenance of embryo freezing need frequent use of liquid nitrogen to fill the cryo tank. Fixed charges should be paid periodically once in every 6 months or every 12 months until they are transferred or discarded.

What is the survival rate of frozen embryos when thawed in the future?                                                                                                                                Survival of the embryos depends upon the quality of the embryos at the timing of freezing. Embryos are more stable and with the new vitrification technique, survival is more than 90-95% after thawing.