One in seven couples experience difficulty in conceiving and many of them will require in vitro fertilisation (IVF). IVF involves hormone injections to stimulate a woman's ovaries to produce eggs which are then removed by a minor operation and mixed with sperm to create embryos in the laboratory. Usually these embryos are replaced within the uterus in 3 to 5 days. This is called fresh embryo transfer. Any remaining embryos are usually frozen so that they can be thawed and transferred at a later date if required - a process known as thaw frozen embryo transfer. Both forms of embryo transfer are commonly used as part of routine IVF treatment.
There have been some small studies, which suggest that using thawed frozen embryos may lead to improved pregnancy rates. This is because when frozen embryos are used, there is a delay in embryo transfer of between one and three months, allowing the excess hormones of ovarian stimulation to wear off, giving the uterus time to return to its natural state.
However, as only a few, small studies have currently been done, we do not know which procedure is better for IVF treatment and without further research we cannot say whether fresh or frozen thawed embryo transfer leads to a higher number of healthy babies born. The E-Freeze study will compare these two procedures of embryo transfer in 1,086 couples from IVF centres throughout the UK over the next 2 years to find out which one will give the best chance of having a healthy baby or whether there is no difference at all. Whilst there may be no benefit to being in either treatment arm (fresh or frozen thawed embryo transfer) any risk or adverse effects are unlikely.