Maternal and fetal nitric oxide production in normal and abnormal pregnancy.

OBJECTIVES To characterize maternal and fetal nitric oxide (NO) production in normal and abnormal pregnancy by measuring nitrate (NO3-) and nitrite (NO2-) metabolites in maternal venous blood, umbilical venous and arterial blood and amniotic fluid. METHODS This was a prospective cross-sectional study in 160 singleton pregnancies: 60 with one complication (infection, n = 37; gestational diabetes, n = 12; pre-eclampsia, n = 11) and 103 normal controls. Nitrate plus nitrite levels were assayed by reduction with Griess reagent. Comparisons were: maternal vs. fetal compartments; normal vs. abnormal pregnancy; and early vs. late pregnancy. RESULTS Amniotic nitrate and nitrite levels increased from early to late normal pregnancy (20.79 to 28.42 micromol/l, p < 0.02), decreasing slightly at term, and increased from early to late abnormal pregnancy (23.29 to 39.18 micromol/l, p < 0.0001). Late pregnancy levels were higher in abnormal vs. normal pregnancy in amniotic fluid (36.25 vs. 21.70 micromol/l, p = 0.003) and maternal blood (25.80 vs. 18.26 micromol/l, p = 0.002). Overall levels were higher in amniotic fluid than in maternal plasma, and in fetal compartments than in co-sampled maternal plasma (p < 0.005, vs. normal pregnancy). CONCLUSIONS NO metabolite levels increased through normal and particularly abnormal pregnancy, predominantly in the fetal compartments, suggesting that NO production is an additional instrument in the fetal control of the intrauterine environment.