Embryo cryopreservation is an established method of fertility preservation providing suitable couples needing fertility preservation with a predictable chance of future pregnancy based on the number and quality of embryos preserved.
Its success and safety is supported by its routine place within in vitro fertilisation (IVF) programmes, where it is commonly used as means of storing surplus embryos after IVF.
What is Embryo Freezing?
Embryo freezing is a process where embryos are frozen under controlled conditions, embryos are cooled and stored at extremely cold temperatures (-196°C) which suspends their development. Once frozen, embryos can remain in liquid nitrogen for years without deterioration before being thawed and, if they survive and develop well, transferred to the woman’s uterus during a frozen embryo transfer [FET].
Freezing good quality embryos is required in IVF, as it offers couples to go for repeat attempts of frozen embryo transfer after an unsuccessful fresh embryo transfer.
It also gives a chance of fertility preservation for couples who wish to prolong having babies. Some patients have had babies more than ten years after their embryos were originally created and frozen.
Using thawed frozen embryos gives the possibility of a brother or sister for a patient’s baby from a single cycle of IVF or ICSI treatment.
Who may benefit from embryo freezing?
Couples who achieve many good quality 'spare' embryos, following embryo transfer, which can be stored for possible future attempts to conceive patients who have had an egg collection for IVF or ICSI treatment, who have been advised not to go ahead with a fresh embryo transfer will have their embryos frozen for use in treatment at a later date.
A woman in a relationship, about to undergo medical treatment that may make her infertile in the future can have embryos created and frozen before the treatment to give her the chance of having children with her current partner, at a later date.
How are embryos frozen?
Suitable embryos are placed in labelled straws in cooling solutions and then stored in tanks of liquid nitrogen at -196 C.
- To be suitable to freeze, embryos must:
Be at the correct developmental stage for the number of days the embryos have been cultured; for example two days after fertilization an embryo should be four cells
- Contain cells which are approximately the same size which indicates regular division
- Contain less than 25% fragmentation
Have well-defined membranes indicating that they are not undergoing a delicate cellular division at that precise moment.
- Embryos may be frozen at various stages of development:
- 2PN Stage: the day after egg collection
- Cleavage Stage: four to eight cells, two or three days after egg collection
- Blastocyst Stage: when the multi-cellular embryo has hatched, usually five or six days after egg collection
- Embryos are stored in cryocans at CARE IVF which are regularly inspected
For how long may embryos be stored?
Legislation determines the time that, with patients’ consent, is allowed to store embryos. Currently embryos may be stored initially for 10 years. Under exceptional circumstances, storage may be extended up to 55 years from the date of freezing (to be reviewed every 10 years), if the patient, partner or someone to whom the embryos are allocated is prematurely infertile or likely to become prematurely infertile.
Does Embryo Freezing improve IVF success rates?
Recently Embryo Preservation gained importance due to its help in enhancing standard IVF pregnancy rates through elimination of embryo- endometrium asynchrony and the association with implantation failure.
Furthermore, studies have also de-mystified myths that frozen embryos may have reduced pregnancy rates than fresh embryos.
Certainly data from the American Society for Assisted Reproductive Technologies 2011 National Summary Report confirmed that pregnancy and live birth rates between frozen non-donor embryo transfers and fresh embryo transfers were comparable. Of all non-donor frozen embryo transfers, 44.6% resulted in pregnancy, compared with 43.9% of fresh transfers, with an overall live birth rate of 34.5% for frozen transfers, compared with 35.8% of fresh transfers.
Long Term Embryo Storage
KSOB is one of the largest cryo-banks in the eastern India. The embryos once frozen can be stored for a period of 10 years. The freezing charges need to be paid annually.
Who can opt for embryo preservation?
- Couples with Primary Infertility undergoing IVF can store their excess embryos till future cycles.
- Couples wishing to delay having their second child can opt for embryo preservation.
Couples in egg donor programs where synchronising donor and recipient may be a problem– can opt for the embryos created using donor oocytes to be frozen till they plan the transfer to the recipient.
Couples looking for pregnancy via surrogacy would need to freeze their embryos till a surrogate is ready for transfer.