Fresh versus frozen embryos - which are better ?
In the past, we believed that the pregnancy rates with fresh embryos were better. Today, we know that frozen embryos have a higher success rate, when the technique of vitrification is used
A few years ago, the answer to this question would have been simple. The traditional teaching has always been that fresh embryos are better than frozen embryos . They have a better chance of becoming a baby - in scientific jargon, they have a higher implantation rate.
However, we are now starting to realise that this is not true.
In a typical fresh IVF cycle , we need to superovulate you . The hormones which are used for helping you to grow many eggs can also mess up your uterine lining , so it's not optimally receptive for implantation. This is why mini-IVF and natural cycle IVF is becoming popular again. Studies have shown that the implantation rates ( pregnancies per embryo transferred) are higher in natural cycles as compared to superovulated cycles, when the embryos are of the same quality.
This is why patients maybe better off transferring frozen embryos , so that the uterine lining is optimally prepared to make it receptive for implantation.
In the past , the only technique we had for freezing embryos was the slow freezing protocol. This was not very efficient, and many embryos would get damaged while freezing and thawing. The survival rates were poor even in the best of labs, because the slow freezing protocol itself was suboptimal. It damaged blastomeres because of ice crystal formation within the cells and the cryoprotectant chemicals used could not consistently prevent this damage .
Today, all that has changed with vitrification ! Survival rates are better than 98 % and we are certain that all the cells ( blastomeres) of the embryos will survive when thawed ( if done properly by a skilled embryologist).
This major advance has changed IVF practise completely !
For one thing, we don't need to transfer too many embryos at at time. As I tell my patients, we can transfer as many as you like, but only 1-2 at a time ! Thanks to the fact that we can promise our patients that the supernumerary embryos we are freezing for them will be safe and sound when we need to use them, patients are quite willing to accept single embryo transfers, because they know that they are not throwing away or wasting their hard-earned precious embryos.
Frozen thaw IVF cycle are much easier for the patient . We just need to do 1-2 scans - which means they are much less stressful and disruptive, and much easier to repeat. They are also much less expensive ! This allows us to reduce the risks of high order multiples; while offering our patients excellent cumulative conception rates !
However, please do remember that not all clinics are good at vitrifying embryos. This is still quite a new technique; and does require the embryologist to be experienced and skilled. There's a steep learning curve associated with vitrification - and many embryologists will end up killing embryos while learning to vitrify them, because they are not quick enough ! If you want your frozen embryos to be treated with the love and respect they deserve, please make sure you choose an experienced clinic which has a full-time expert embryologist working for them. Also, always ask the clinic to provide you with photos of your embryos - before they have been vitrified ; and after they have been thawed !
