Hi! I'm Dr. Randy Morris. I'm a board-certified fertility expert and the
medical director at the world-renowned IVF1 fertility center in Naperville
Illinois and this is infertilityTV. [music]...... If you have suffered a miscarriage or
multiple miscarriages chances are you've gone online and done a Google search to
try to figure out what the cause for the losses was. And if you did that, you
probably came across some web page that talked about natural killer cells.
This probably terrified you because what sounds scarier than killer cells
attacking your pregnancy? Here is the basic idea: They do a blood test to look
at how many natural killer cells there are. If your levels are high, that means
you're at greater risk for a miscarriage. In order to prevent miscarriage,
you do a really expensive therapy called intravenous immunoglobulin or IVIG.
Unless you do this, you are doomed to have miscarriages over and over.
Sounds reasonable right? Unfortunately it's completely wrong. Natural killer cells
are one type of white blood cells and are therefore part of the immune system.
They circulate in the blood and they can also be found in the uterine lining.
In the blood, natural killer cells work as an early defense to destroy cells
infected with viruses and cancer cells. However, in the uterus these cells are
not cell killers; in fact, they are distinctly different than the natural
killer cells in the blood and have a completely different function. So let's
not call them natural killer cells anymore, let's refer to them the way
scientists do which are "NK cells". The most recent research suggests that
NK cells in the uterus are essential to allow the embryo to implant and allow
the placenta to grow. In the uterus, in fact, uterine NK cells increase in number
after ovulation. around the time that an embryo is expected to implant.
These levels stay high during pregnancy. So measuring the
number of NK cells in the blood or in the uterus is a useless test. So what are
all these NK cells doing in the uterus? In order to answer that question we need
to ask another question first and that is: How is it that an embryo which is
foreign to the mother is not rejected by her immune system like a liver or kidney
transplant? The answer is that the mothers immune system somehow learns not
to reject an embryo. This is called "immune tolerance"
Recent evidence suggests that uterine NK cells are involved in the process of allowing
immune tolerance to embryos. Now in certain cases, based on the
mother's genetic makeup and the father's genetic makeup the mother may fail to
develop tolerance to an embryo. There may be some embryos which therefore get rejected
by the mother's immune system. This may be more likely to occur in
situations like egg donation where there is twice as much tissue which is foreign
to the mother. This is an area of active research. In the meantime, don't waste
time and money doing blood tests for NK cells or biopsies of the uterus for NK
cells and certainly don't have treatments like IVIG which are risky and unproven.
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