Natural Killer (NK) Cells are cells produced by our immune system to defend us against foreign invaders such as viruses and tumour cells. They are mostly found in the uterus in females. The level of NK cells increases during menstruation and highest during pregnancy, that is when the embryo is implanted in the uterus. Unfortunately, sometimes, these NK Cells mistakenly identify placenta and foetus as a foreign threat and this possibly leads to miscarriages during the early stages of pregnancy or problems during the pregnancy period. This is usually brought to notice via swelling near the pelvic and uterus. Hence a Natural Killer Cells Test is needed in such cases to detect and regulate the activity levels of these cells.