ABSTRACT
INTRODUCTION: The Doppler method is extensively applied today for the evaluation of pregnancies with involvement of the uteroplacental blood flow. Although increased nitric oxide (NO) formation plays an important role in regulation of systemic vascular resistance during pregnancy, growing evidence indicates that reduced NO formation is associated with hypertensive disorders of pregnancy, especially preeclampsia. OBJECTIVES: The studies were to assess the maternal and fetal Doppler parameters and to determine the whole blood nitrite levels during pregnancy. METHODS: Thirty-three healthy pregnant women were evaluated during the first (11-14 weeks), second (20-24 weeks) and third trimesters (34-36 weeks) of pregnancy. The maternal (uterine arteries) and fetal (cerebral and umbilical arteries) vessels were evaluated by Doppler velocimetry. venous blood was collected(15mL) for the determination of plasma nitrite by chemiluminescence. RESULTS: Regarding the Doppler parameters of the uterine arteries the mean pulsatility index was 1.73, 1.06 and 0.73 in the first, second and third trimesters of pregnancy, respectively. Fetal Doppler showed a mean resistance index of 0.82 and 0.81 for the middle cerebral artery, 0.73 and 0.60 for the umbilical artery in the second and third trimesters, respectively. The mean plasma nitrite concentration was 189.10, 178.28 and 199.57 nmol/ml in the first, second and third trimesters of pregnancy, respectively. CONCLUSION: The study demonstrated that a fall in flow resistance occurs in the uteroplacental vessels without changes in plasma nitrite concentrations during pregnancy.