Fertility clinics are increasingly offering women tests to measure the number and activity of natural killer (NK) cells circulating in their blood. These cells are found in the womb (uterus) and accumulate in large numbers during early pregnancy, but their function is completely unknown.
The tests are based on the speculation that women with recurrent miscarriage and infertility have raised levels of NK cells. As a result, many women are offered powerful treatments, such as steroids or immune suppressant drugs, to reduce the levels of NK cells.
But the authors argue that, not only do these tests give no useful information about what is happening in the uterus, these treatments are not appropriate for use in reproductive medicine without shown benefit as they are associated with known risks to mother and fetus.
Recent guidelines from the Royal College of Obstetricians and Gynaecologists, plus two randomised studies, have also concluded that there is no evidence to show they are beneficial.
Understanding the function of uterine NK cells is certainly a major challenge in human reproduction, they say. However, until more is known about their role in normal pregnancy, there is no evidence of any benefit in offering NK cell testing in women with recurrent miscarriage and infertility outside of properly controlled studies.
"This unfortunate group of women are particularly vulnerable to financial exploitation, and of being exposed to powerful treatments that have, as yet, no rational scientific basis," they conclude.