Alexandra Izquierdo, MD
Medical Director at IVF-Spain Madrid (Former Clinic), IVF-Spain Madrid
Embryo Implantation, Failed IVF Cycles, Success Rates
“Implantation is the last frontier in assisted reproduction”, said pioneer of in vitro fertilisation, Dr Robert Edwards, and when thinking about IVF, it really is the final hurdle, following hormone injections, fertilisation and the creation of a, hopefully, healthy embryo.Implantation must happen, in order to create a pregnancy, yet, sadly, even after IVF, implantation is not a given, even with a top-grade embryo. Of course, having a good quality embryo is key and each day an embryo survives, in a laboratory situation, embryologists are able to garner further information, about its viability, providing increased knowledge as to which embryo/s will offer a higher chance of implantation. Pre-implantation genetic screening (PGS) also enables greater insight into embryonic health. However, alongside a good quality embryo, there are many other factors which can affect whether, or not, an embryo will implant. Implantation happens when the outer shell, of the embryo, attaches to the cells of the uterine lining, it’s therefore incredibly important that a woman’s body is well prepared, for the transfer; her hormones have to mirror and be in synch with what would happen, during a natural cycle, creating, what Dr Izquierdo describes as; “the window of implantation”. For a pregnancy to occur naturally, the female body goes through various hormonal changes to prepare for receiving a fertilised oocyte (egg). Ovulation (the release of the egg) occurs, typically monthly, and the hormone oestradiol is produced; oestradiol is the main oestrogen found in women, and one of its functions is to induce the endometrial lining to thicken, preparing itself for the attaching of an embryo. If an egg is fertilised, during a natural cycle, and implants, the newly pregnant body then enters, what is referred to as, the luteal phase, whereby the corpus luteum naturally produces the correct amount of progesterone, required to support early pregnancy. Progesterone stimulates the growth of the blood vessels, which supply the uterine wall, and stimulates glands, in the endometrium, which then nourish the early embryo, helping it to become a viable, ongoing pregnancy. All of which needs to be replicated, when undergoing assisted conception; if there is a hormonal imbalance or thinner uterine lining, then an embryo is likely to struggle with implantation.
There is also some controversy surrounding NK (Natural Killer) cells testing, but, again, Dr Izquierdo advises it’s worth testing in women with recurrent implantation failure and miscarriage.NK cells are thought to kill the outer shell of the embryo, thus making implantation impossible. If a patient tests positive, for NK cells, then there are possible treatments, which can be suggested, to see whether the chances of implantation and ongoing pregnancy, can be improved. Whilst embryo quality is the main factor responsible for implantation, it’s important to remember that it’s not the only determinant. Uterine and hormonal health is of great importance too and, whilst some tests may currently not be conclusive, more studies are taking place, and data is being collated, so that medical scientists can improve their knowledge and further understand how to help healthy embryos implant. Each patient is unique and personalised treatment truly does play a huge role in the final frontier, of IVF.