I remain concerned that when IVF doesn’t work, a patient is too often given a diagnosis of carrying high levels of Natural Killer (NK) cells in her uterus, preventing implantation. In fact, it’s far more likely to be a problem on the embryo side — often related to older eggs — and the reality of this can be tough to face. If it was a case of “well, looking for them and treating them can’t do any harm”, the situation might be more acceptable. However the diagnostic tests for NK cells are not well validated (meaning there may be lots of false results), and the commonly used treatment of prednisone (corticosteroids) may carry higher risks to mother and fetus. Here’s a very reasoned view from the UK about this issue. I agree strongly with the comments.