Plasma and amniotic fluid concentrations of nitric oxide: Effects on uterine artery and placental vasculature in women who underwent voluntary pregnancy termination and in women with missed and threatened abortion. A pilot study.

Objectives: First trimester miscarriage is a multifactorial event. Various angiogenic factors have been proposed as possible early markers of non-viable pregnancies. The aim of the present study was to evaluate the systemic nitric oxide (NO) production in healthy early pregnancy and its possible role in first trimester miscarriage.

Study Design: We prospectively enrolled women referred to our Unit for elective termination of pregnancy, threatened abortion or missed abortion. Blood samples were taken for testing circulating NO plasma levels. Subsequently, all patients underwent 2-D ultrasonographic analysis and Color Doppler imaging to assess the pulsatility index of the uterine arteries. 3-D ultrasonographic and power Doppler analysis allowed a volumetric and vascular reconstruction of the placenta. During dilatation and vacuum aspiration, amniotic fluid was collected.

Results: Seventy-two patients were enrolled: 25 with elective termination of pregnancy (Group I); 17 with threatened abortion (Group II); 30 with missed abortion (Group III). Group II showed greater placental volume and lower uterine arteries PI than others. The plasma NO concentration resulted statistically higher in women with threatened abortion, while amniotic fluid NO concentration were higher in the viable pregnancies (Group I) than in the aborted fetuses (Group III). Plasma NO was inversely correlated with both mean arterial pressure and uterine artery PI and was positively correlated with amniotic fluid NO and CRL; amniotic fluid NO was positively correlated with placental Vascularization Index and Vascularization-Flow Index.

Conclusion: Amniotic NO concentration was higher in viable pregnancies and positively related to Doppler 3D indices of vascularization and blood flow within the placenta. Further studies are needed to elucidate its role in first trimester miscarriage.