Natural Killer cells, immune tests and fertility

Immune tests and therapies have been used over time to identify and treat patients with implantation failure and or recurrent miscarriage.

Evidence from researchers, especially in the UK provide a better understanding of immune function, its role in implantation, validity of available tests, as well as efficacy of treatments.

Natural Killer (NK) cells

Natural Killer (NK) cells are immune cells present in circulation (blood NK cells) as well as in the womb (uterine NK cells).

For many years, it was assumed that a blood test to measure NK levels in circulation would help identify those patients with high NK levels in the womb. They were then offered treatments to reduce NK activity, to hopefully increase success rates following fertility treatment.

However, recent research has confirmed the following:

  • Uterine NK cells are not found in the blood. They occur only in the lining of the womb during early pregnancy, while the embryo is implanting itself there and the placenta is developing. We cannot therefore test them from a blood test.
  • The levels of blood NK do not co-relate with of uterine NK levels. Therefore most clinicians and researchers strongly doubt whether any meaningful information about uterine NK cells can be obtained from a blood sample.
  • There is no evidence that uterine NK cells are destructive and attack placental or embryonic cells. However, heightened activity possibly exposes the embryo to high oxygen levels which may affect implantation.
  • No commercially available tests have been developed for uterine NK cell levels.
  • In a research setting, a small study showed that patients with recurrent miscarriage and high uterine NK levels may benefit from steroid treatment.

So what tests or treatments could be offered?

Unfortunately there are no reliable tests for uterine NK levels which would enable us to identify patients that may benefit from immune treatments.

However, in cases of repeated implantation failure/recurrent miscarriage, low dose steroid therapy may be offered empirically (i.e. as a trial therapy). This is because no tests are available to prove that a particular patient needs it, though there is some evidence that if one had high NK levels, it may be of some benefit.

If you would like to discuss this further with one of our fertility specialists then please contact us to make an appointment – we can usually see you for an appointment within 1-2 weeks.

For further information, visit the HFEA link for a full review.

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