Freezing sperms, eggs or embryos at sub-zero temperatures gives a person / couple the opportunity to have a child at a time of their choosing later in life. So, if your current focus is financial stability or career growth, pregnancy can be kept on the backburner without having to worry about the quality of eggs and sperm decreasing with age. Freezing embryos is also an integral part of all IVF programmes where a high number of embryos are generated. These can be used either if the first attempt fails or to have another pregnancy later in life.
Cryopreservation or freezing simply is a process where the temperature is gradually lowered so that all the activities of the cell remain intact. Earlier, it was done by a technique called slow freezing which had lower survival rates (60-70%). Today, it is replaced by vitrification or rapid cooling with survival rates of almost 100%. The tissues are first protected by a cryoprotectant solution which drains water from the tissue. Tissues are then preserved in containers filled with Liquid Nitrogen, at -196o C. Eggs, sperms and embryos can be stored at such temperatures for an indefinite period, but storage incurs a cost, so the storage time period depends on the needs of the person who is storing them. When the person / couple decides to conceive, the frozen sperms/ eggs / embryos are rehydrated by ensuring that the embryo doesn’t blow up. This process is called thawing or warming.
Cryopreservation is used in two situations :
1. Fertility preservation : Either due to a disease (malignancy, endometriosis, autoimmune) which is likely to impair the reproductive potential or due to elective social reasons (career, financial stability or otherwise)
2. As a part of IVF process where extra embryos are stored for future usage.
It is well established that the quantity and quality of a woman’s egg decreases with age especially after the age of 35. In fact, age is one of the most common infertility risk factors. Because of this, many couples prefer to create embryos when they are young and freeze them so that they can have babies later. Experts suggest those mulling about freezing eggs / embryos should do the procedure before the age of 30-33 years, when the eggs and sperm are relatively healthy.
In all IVF procedures, drugs are given to stimulate the ovaries to produce more eggs. Hence, many a times there will be higher number of embryos. All such surplus embryos can be frozen and used later – for a second child when the first attempt is successful or for a second attempt if the first one fails.
In men, testicular tissue or sperms may be frozen whereas in women eggs or ovarian tissue may be frozen. In a couple, it is advisable that embryos are created and frozen. Social freezing is performed when a person / couple is not ready to have a child and want to delay it for career or other reasons. Freezing gametes / embryos at a young age gives them a better chance when they want to have a pregnancy at an older age.
This process involves thawing of a previously cryopreserved embryo and transferring it in the uterus after optimal endometrial preparation.
A frozen embryo transfer is a much simpler process and does not require any injections or anesthesia for egg extraction. It involves intake of oral and vaginal tables to prepare the uterus for the pregnancy.
The cost of frozen embryo transfer is significantly less compared to a fresh IVF cycle
The success rate of embryo transfer using frozen and subsequently warmed embryos is equivalent to a fresh transfer.
Frozen embryo transfer freezes the age: It gives the same success rate as that of the biological age at which the embryos were frozen. For e.g. if a women undergoes an IVF cycle at 28 years and conceives and freezes the extra embryos, even if she plans another child at 35 years, she will get the same success rate with the frozen embryo transfer as before (equivalent to what she had at 28 years )
Patient is called on Day-2 of the menstrual cycle. On that day, an ultrasound is performed, and oral estradiol tablets are started. The next visit is usually after 8-10 days when an ultrasound examination is performed to check the growth of the endometrium. If the endometrium growth is optimal, progesterone tablets are added and depending on the stage at which the embryo was frozen, the embryo transfer is done.
A blood test is done after 2 weeks to check for pregnancy
Eggs and Embryo – what is the difference?
Egg freezing is used when the woman is not married or does not have stable partner. The process is the same stimulating the ovary to produce multiple eggs, removing the eggs followed by vitrification and storage in liquid nitrogen. The difference, however, is in how it can be used when needed. The egg has to be thawed or warmed (brought out from -196 C to room temperature), checked for survival and fertilized with sperms to generate embryos which are then transferred in to the uterus. All eggs may not survive (survival is generally 90 95 %), all eggs may not fertilize and generate embryos (this is generally 50 60 %). Whereas in the case of embryo freezing, embryos are created before they are frozen and when needed simply thawed (> 95 % survive) and used. So, we need a much higher number of eggs to achieve the same results that is obtained by embryo freezing. This number depends on the age of the woman and egg quality.
What if the embryos remain unused after being frozen?
Embryos frozen for a couple can either be used by the Couple or they have to be discarded or donated to a recognized research body for medical research. They cannot be donated to another person / couple. If one of the partner dies or the couple gets divorced, the embryos are given to one of the partner based on the consent given at the time of freezing. Freezing embryos is an excellent way to maintain the quality of embryos while delaying a pregnancy.