Frozen Embryo Transfer (FET)

The first baby born from an embryo that was frozen occurred only seven years after the first IVF baby was born. Since that time the percentage of treatment cycles that are frozen cycles has increased yearly and now a quarter of all cycles of treatment in the UK are with frozen embryos. There are no risks to the health of babies demonstrated from embryos being frozen. Some evidence shows that babies born after frozen embryo transfer have a slightly lower chance of pregnancy complications, such as having a lower weight, preeclampsia and  being born early. All these differences are very small and it is not recommended that all treatment is with frozen embryos because of these small differences. 

No. There are some subtle differences in embryo grading, but essentially if an embryo is deemed suitable for freezing it is a top quality embryo. The success rates in terms of pregnancy will be the same as that embryo which at the time of fresh transfer was chosen as it showed some slight grading superiority.

No, there is no evidence to demonstrate that the duration of freezing has any effect on outcomes in terms of survival rates or pregnancy. The longest time an embryo has been frozen, thawed and used to achieve a successful healthy pregnancy is 24 years.

If your embryos were frozen with Northwest Fertility they will have been frozen using a technique called vitrification, also known as rapid freezing. This technique has been shown to be more effective at protecting embryos from the effects of freezing particularly when frozen as a blastocyst. Each embryo will be frozen individually in a special labelled straw.

The major risk of damage to the embryo from freezing is due to the formation of ice crystals at the time of freezing. To protect them from this they are frozen very rapidly in a special solution that protects them from the effects of freezing. Using this technique the embryologists will expect that 90-95% of embryos will survive being frozen and thawed and be available for transfer.

If your embryos were frozen at another unit using the older slow freeze technique then the survival rate of embryos by freezing falls to around 70-75%. If your embryos have been frozen at an earlier stage in their development as a day 1 or day 3 embryo then these embryos may not reach a stage suitable for transfer at day 5.

For both natural and stimulated cycles treatment is usually the time taken for a normal menstrual cycle. If you are using a natural cycle you will be asked to contact the unit with the first day of your cycle, a scan will be undertaken around day 10 of your cycle to confirm that you are likely to ovulate and the lining of the womb is developing normally. You will be asked test for ovulation using an ovulation testing kit and inform us when you have a ovulation hormone surge, the embryo will be thawed on the day of embryo transfer, six days after the surge. 

If you are undertaking a stimulated cycle you will start daily injections around 6 days prior to your next expected period. You will be asked to ring with the first day of your bleed to organise a scan in the following week. This scan will confirm that your hormones have been switched off and that you are ready to start thickening the lining of your womb in preparation for your embryo transfer. You will be given a date to start oestrogen tablets and given a schedule indicating your next scan (around day 10-13 of tablets) as well as a planned date to start your progesterone and a likely date for your embryo transfer. This medication will be continued to 10-12 weeks of any resulting pregnancy.

For all cycles the principle form of monitoring is an ultrasound scan around day 10-13 of your treatment cycle which allows the clinician to ensure the appropriate development of the lining of the womb. 

You will be asked to complete a new consent to frozen embryo transfer form and Zika declaration before each and every treatment cycle of frozen embryo transfer, this is required by the Human Fertilisation and Embryology Authority (HFEA) to ensure that both you and your partner are happy to continue with treatment.