The Effect of Low Molecular Weight Heparin in Recurrent Pregnancy Loss: Changes in Radial Uterine Artery Blood Flow and Peripheral Blood NK Cell Fraction

Abstract

Immunological alteration has been suggested as a cause of unexplained early recurrent pregnancy loss (RPL). Natural killers (NKs) have been reported to play a role in vascular remodeling of decidual vessels. We aimed to find out if there is a relationship between peripheral blood NKs (pbNKs) and uterine radial artery (uRA) blood flow, and if low molecular weight heparin (LMWH) is effective in improving uRA blood flow in RPL cases and pregnancy outcome. The study was conducted on 30 pregnant women (5-7 weeks gestation) with ≥ 2 RPL and control group including 30 healthy pregnant women. The frequency of pbNKs (CD3 negative/CD56+CD16 positive) was measured using flow cytometry. Uterine color-pulsed doppler ultrasound was performed to evaluate uterine radial artery resistance index (uRA-RI). LMWH was administered daily in RPL cases with elevated uRA-RI (≥0.5) and uRA-RI was reassessed one week later. Comparison between cases and controls revealed that uRA-RI was significantly higher in RPL cases than controls (P =0.023), while pbNK frequency showed no significant difference between both groups. Post LMWH treatment, uRA-RI was significantly decreased when compared to pretreatment uRA-RI with mean±SD= (0.48+0.08) and (0.68±0.09) respectively (P=0.007). There was significant correlation of uRA-RI with number of abortions. There was no significant correlation of pbNK% with URa-RI (r=0.125 P=0.509) in RPL group. We concluded that LMWH treatment carries potentiality of improving pregnancy outcome in cases of RPLs with elevated uRA-RI. No significant correlation of NK% with uRA-RI, which denies the association of pbNK and RPL and raises questions about impact of pbNK cell testing in RPL.