Egg freezing is a novel technique. The first successful report of normal development of cryo frozen human oocytes to hatching blastocyst stage was in the year 1995 by Gook et al.
Q1. What is oocyte freezing?
Ans. Oocyte freezing is a relatively new technique in which eggs can be stored at temperatures below freezing point. The procedure of egg retrieval following ovarian stimulation is similar to that IVF. Once the eggs are retrieved they are placed in a freezing solution and then cooled very slowly using assisted freezing machine. These are stored at temperatures below – 196oC for an unlimited period and then can be used whenever required.
Q2. Who are the candidates for oocyte freezing?
- Women undergoing chemotherapy or radiotherapy for the treatment of cancer can freeze their eggs before commencing the treatment, for future fertility.
- Women with a higher chance of having premature ovarian failure
- Women less than 35 years who wish to preserve the eggs for future use as they either do not have partners or due to medical reasons.
Q3. How successful is egg freezing?
Since the technique is relatively new, it is difficult to predict the outcome but worldwide about 100 babies have been born through this process.
Q4. Are the babies born after oocyte freezing normal & healthy?
Ans. Studies done so far on mouse as well as human oocytes suggests that freezing does not damage the intricate structures within the egg. But the safety of the procedure is yet to be proved.
Embryo Freezing –
Cryopreservation of embryos has led to tremendous improvement in the pregnancy rate and cumulative success rate possible following a single cycle of IVF.
Q. How is Embryo Freezing done?
Embryo freezing is a well established technique. The first frozen embryo baby was born in 1984.
The good quality embryos that are left after embryo transfer are mixed with a special media called cryoprotectant. These are then loaded into straws which are sealed and then placed in a Freezer which slowly decreases the temperature by 0.3oC till it reaches - 79oC. Thereafter the straws are stored in liquid nitrogen containers at -196oC. These may be used anytime in the future.
Q. What are the risks involved with embryo freezing?
The frozen embryos are labelled and kept in liquid nitrogen containers. With only theoretical loss being due to the damage caused by ice crystallization, the embryos will remain viable.
Q. What is the survival rate after freezing and thawing?
The survival rate following freezing and thawing, in a good centre, is almost up to 70-80%.
Q. What is the procedure for frozen embryo transfer?
The frozen embryos can be transferred into the uterus in a natural cycle, stimulated cycle or a hormone treated cycle with similar success
Q. What are the advantages of cryopreserving embryos?
- Increases the chances of conception following a single IVF cycle
- In women with high risk of PCOS, embryos are frozen and transferred later
- In women with a poor endometrium, bleeding at the time of transfer or endometrial polyp, embryos can be frozen and then transferred in a subsequent cycle
- If the fresh embryo transfer is difficult due to cervical stenosis cryopreservation is useful
- Before starting cancer therapy, embryos are frozen for future use
Vitrification is the solidification of solution into a glassy vitreous state by increasing the speed of temperature conduction. High concentration of cryoprotectant helps to bring high viscosity during cooling. It is an ultra rapid method of embryo freezing.
Advantages of vitrification:
- Direct contact between cells / tissue and liquid nitrogen
- No ice crystallization
- Utilizes higher concentration of cyroprotectant that enables shorter exposure time to the cryoprotectant.
- Speedy vitrification / warming
- Small volume used provides a big increase in the cooling rate
- Cooling rates from -15000 to 30000C / min
- Minimizes diffusion injuries
- Reduces the time of cryopreservation procedure (duration from 2 to 10 mins)
- Simple procedure
- Eliminate the cost of expensive freezing equipment
Embryo cryopreservation has become a well established technique in ART. At our centre we tend to preserve the embryo at 2-8 cell stage and even at blastocyst stage either by typical slow cooling or by vitrification. The major aim of embryo cryo preservation is to provide opportunities for conception and fresh transfer. It additionally contributes to lowering the danger of severe OHSS
Q. What is sperm freezing?
Semen cryopreservation is the freezing and storage of sperms at low temperatures at which all the metabolic processes are arrested
Q. What are the reasons for sperm freezing?
A. Long term freezing is indicated for men:
- Who are undergoing chemotherapy or radiotherapy which may lead to sterility?
- Before vasectomy
B. Short term freezing is indicated for man:-
- Who find it difficult to give the sample for IUI/IVF?
- With variable sperm count
- Who cannot be present at the time of IUI/IVF
Q. What is the procedure for semen freezing?
After collecting the semen volume, the sample is analyzed for volume, viscosity, pH, total count, motility, morphology etc. A small volume of cryoprotectant is added for preventing the damage due to freezing. These are then divided into aliquots and subjected to freezing which are then stored in liquid nitrogen at -196o C
Q. What is the success rate of using frozen sperms?
The success rate is almost similar to that of fresh sperms except that moulity of frozen thawed sample decreases rapidly within 12 hours. Further the chances of transmitting HIV infections are minimal.