The Role of Peripheral Natural Killer Cells in Recurrent Spontaneous Abortions

Recurrent spontaneous abortion (RSA) is defined as three or more consecutive miscarriages, which affects 0.8 to 1% of pregnant women. Despite several well-established etiologic factors, the cause of RSA cannot be determined in almost 60% of the cases. It has been postulated that a part of these repeated pregnancy losses might be due to immune causes.

In the present case control study using flowcytometry, peripheral NK cytotoxicity was compared in three different groups. 21 women with history of RSA at the time of 3rd or higher abortion (Group I), 32 women with history of three or more previous abortions and at least three months had lapsed since the last abortion (Group II) and 32 pregnant women with no history of abortion and at least one successful pregnancy (Group III) were studied.

Group I and Group II showed significantly higher NK cytotoxicity than Group III in all of the effect to target (E: T) ratios (P≤0.045 and P≤0.002 respectively). NK cytotoxicity was similar in groups I and II. There were no significant correlation between the number of abortions, age and NK cytotoxicity.

The results indicate an increased peripheral NK cell cytotoxicity in RSA groups as compared to pregnant control. NK cell cytotoxicity may be considered as a risk factor for RSA and for maintaining normal pregnancy, NK cell cytotoxicity may be down-regulated. Peripheral NK cytotoxicity is not elevated during first trimester in RSA women. It is suggested that detection of NK cytotoxicity in RSA women should be performed as a routine.