Why embryo implantation fails ?
The course of evolution has armed the body with white blood cells to fight infections. The womb has a special type of white blood cells, called the natural killer cells (NK cells). These cells appear near the surface of the uterine lining and vary in numbers throughout the menstrual cycle as well as at different stages of pregnancy. Infertility specialists have linked an increased activity of these cells with failures in embryo implantation and miscarriages.
One of the limitations of in-vitro fertilization (IVF) is identifying the exact cause of embryo implantation failure. The process of implantation is yet to be completely explored. Immune responses from uterine NK cells (uNK cells) have been implicated as a potential cause of embryo implantation failures in women with good quality embryos and an apparently healthy uterus.
In a recent study, Dr. Divyashree, Dr. Jyothishmathi, and the team from Milann – The Fertility Center evaluated the association between pregnancy and uNK cells among women with a history of implantation failure following IVF.
Majority of the literature focuses on high NK cell activity and failed reproductive outcomes, but it is imperative to note that uNK cell activity, is essential, in moderation for normal implantation to occur.
The study found average conception rates of 29.4%, 35.3% and38.9% in patients with low, intermediate and high numbers of uNK cells. However, the live birth rate among women who had conceived was significantly higher by over 100% in intermediate group when compared with the low and high groups. Thus women with uNK cells in the intermediate range had minimum adverse outcomes and maximum live births. These results are in agreement with previous animal studies by Guimond et al who demonstrated that NK cell deficient Severe Combined Immune Deficiency (SCID) mice have shown poor implantation rates. Further they demonstrated that replenishment of uNK cells by Bone Marrow transplantation in the mice restored the normal dynamics of implantation.
Dr. Kamini Rao, Medical Director of Milann – The Fertility Center shared her views stating that “Dr. Jyothishmathi’s study is probably the first to have suggested a healthy range for uNK cells for optimal pregnancy outcomes in humans.” Future studies can look at a definite range that would help infertility specialists in managing the mechanics of implantation better.