Heard of frozen embryo transfer but don't quite know what it means? This guide has the answers.
When it comes to In Vitro Fertilisation (IVF), every little embryo can seem like a thoughtful little treasure. Which is why saving your leftover embryos from a given IVF cycle can be a wonderful thing.
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IVF treatment is a long process which often involves several attempts at embryo transfer to achieve the final goal of one live-born baby. The process of IVF involves hormonal stimulation to enable the growth of multiple eggs. All of these eggs are fertilised and multiple embryos are created; many more than what one would need for one embryo transfer attempt. These surplus embryos that remain after the first embryo transfer can be cryopreserved or frozen for later utilisation, either if the first embryo transfer is not successful or to have a second child sometime later.
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Frozen embryo transfer (FET) is a technique used in conjunction with IVF, that allows cryopreserved/frozen embryos created in a prior stimulated IVF cycle to be thawed and transferred into a woman's uterus.
The embryos are transferred into the woman's uterus on a specified day of the menstrual cycle. This day is called the 'implantation window' and it signifies the day when the uterus is most receptive to the embryo.
Before the onset of the FET cycle, you will be advised general investigations, a pelvic scan to understand your endometrial thickness and sometimes a hysteroscopy.
After a baseline scan, you will be started on estrogen supplements which will help the endometrium to grow in thickness. When the lining has reached the desired thickness, progesterone is commenced and the FET is planned on a specified date. This protocol may also be combined with suppressive injections called downregulation which can commence on day 21 of the prior cycle.
In the natural cycle FET, no medications are administered. The natural process of ovulation is tracked and the day of ovulation is ascertained using a combination of scan, blood and urine tests. The embryo transfer is planned in the implantation window. On the day of the FET, the embryos are thawed, their survival and quality are checked and then transferred into the uterus.
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Embryos are graded based on their quality before they are frozen. The best quality embryos are the ones who have the best chance of implantation and are the ones preferably chosen for transfer. The survival of the embryos depends upon their prior quality; with the best quality embryos surviving the freeze-thaw cycle and resulting in good pregnancy rates. Our experience reveals that embryo survival is close to 90-95%.
Embryos can be technically frozen/cryopreserved for years. Their quality does not deteriorate over time.
Frozen embryo transfer success rates depend on several factors such as the age of the woman, duration of infertility, quality of the embryos frozen, the day of freezing (day 3 or 5), endometrial thickness, etc. Frozen embryo transfer success rates have surpassed fresh embryo transfer success lately due to advances in freezing techniques. Children born after frozen embryo transfer tend to have higher birth weights and are more likely to be born near term. Success rates following frozen embryo transfer are as high as 50-60% per transfer.
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