A recent eye-catching news article stated: Twins born to parents from embryos frozen 30 years ago breaking the prior record of baby Molly Gibson, who was born in 2020; from an embryo frozen 27 years ago! For nearly three decades these embryos were stored in liquid nitrogen at -196 degree celsius, secure in an IVF laboratory of a Fertility centre. Want to know an interesting fact? The first reported pregnancy in humans from a frozen embryo was in the year 1983! Since then, millions of babies have been born through frozen embryo transfers. Dr Duru Shah, Director, Gynaecworld- The Center for Women’s Health and Fertility shares more such interesting facts.
What is Embryo Freezing?
Freezing of embryos or Embryo Cryopreservation is a vital part of ART (Assisted reproductive technology) services. The procedure involves extracting eggs from the ovaries after stimulating them with certain hormones, fertilising the eggs with sperms in the IVF laboratory, creating embryos and culturing them to a certain day 3 or day 5 embryos before freezing them. In some cycles known as fresh cycles, the embryos are put back inside the uterus in the same cycle when the ovaries are stimulated and the eggs are retrieved. While in frozen cycles, the embryos are frozen and transferred back into the uterus of the same woman at a later stage.
With advancing technology and ultra-rapid techniques called vitrification, freezing of embryos or gametes has enhanced success rates with IVF cycles. Prior to vitrification, embryos were frozen using the slow freezing technique which led to lower recovery of viable embryos after thawing them. The process of freezing enables us to maintain the biological age of the embryos since the most important factor determining the success rate of IVF is the genetic age of the woman at which the eggs or embryos were frozen.
Why do people freeze embryos?
There are various reasons why we freeze embryos. They may be medically indicated or for social reasons such as:
- In PCOS patients/Endometriosis patients: Women with PCOS who have many embryos can develop a complication called ovarian hyperstimulation (OHSS) if embryos are transferred in fresh cycles. Hence they are frozen to be transferred in a much optimal environment and to avoid any complications.
- Patients with endometriosis need to be given a pre-treatment for 2-3 months to get better success rates. Hence we first create the embryos, freeze them, treat them for endometriosis with tablets or injections and then do the transfer.
- Social freezing: Women/couples who want to delay pregnancy due to personal reasons freeze their eggs or embryos.
- Genetic diagnosis/Biopsy of embryos: Couples having any history of a genetic disorder in the family need to get their embryos tested before transferring them. Biopsy also enables us to filter out abnormal embryos before transferring them.
- Prior to cancer therapy: Chemotherapy/Radiotherapy can affect the fertility potential by affecting egg quality and number. Hence, it is advisable to freeze your eggs before starting any cancer treatment.
The good news is that the success rates from both fresh and frozen cycles are largely the same. Few studies vouch for the superiority of frozen cycles over fresh; as frozen transfers promise a better uterine receptivity and also give the patient sufficient time to recover from the fresh cycle, but overall there is no statistical difference between both cycles.
Interesting Facts About Babies Born Out Of Frozen Embryos
There have been many questions regarding the well-being of children born out of frozen cells.
- According to a very recent review study including babies born between 1987-2021, it was concluded that there is a significant birth weight difference between fresh and frozen cycle babies.
- Babies born out of frozen cycles tend to have higher birth weights and lesser risk of preterm deliveries.
- On an interesting note, there is no birth weight difference in twin pregnancies of fresh and frozen cycles! Also, there has been no evidence of any higher risk of birth defects among babies born out of frozen embryos.
- Concerning neurodevelopmental outcomes, a recent 2020 long-term study assessed the developmental status of babies at >2yrs of age after birth from fresh/frozen IVF cycles. They found that babies born out of both fresh or frozen cycles have similar outcomes concerning their fine motor or problem-solving skills!
A new Nordic study including almost 8 million babies compared children born via fresh cycles or natural conceptions with babies born out of frozen cycles. They found that frozen cycle babies might have a little increased chance of developing cancer, but the overall risk was very very low. Hence, more evidence-based data is required to establish global guidelines to consider long-term outcomes of children born via frozen cycles.
There are many centres which only offer frozen cycles since it makes it technically easier for the clinic to schedule their IVF cycles, staff availability and avoid overlapping of cases. Whether this is ethical or not, we surely need bigger studies to justify the use of frozen cycles for all patients needing IVF.