Amniotic fluid nitric oxide and uteroplacental blood flow in pregnancy complicated by intrauterine growth retardation

Objective To examine the correlation between placental nitric oxide production and uteroplacental blood flow.
Participants Thirty-one pregnant women with fetuses with intrauterine growth retardation and 27 normal pregnancies as controls.
Design Correlation between amniotic fluid measurements of nitrite metabolite in the third trimester and flow velocimetry waveforms recorded from uterine, umbilical and fetal middle cerebral arteries. Intrauterine growth retarded pregnancies were compared with controls.
Main outcome measures Concentrations of nitric oxide metabolites (NO₂^- and NO₃^-) in amniotic fluid were correlated with flow velocimetry waveforms findings by the determination of correlation coefficient.
Results Overall median nitrite values in amniotic fluid were higher (   P < 0.01  ) in intrauterine growth retarded patients (median 8.6 μmol/mg creatinine) than in controls (5.6 μmol/mg creatinine). Pathologic uterine flow velocimetry waveforms in uterine artery (-2SD) were observed in 12 women of the intrauterine growth retarded group, and the concentration of amniotic fluid nitrite was significantly lower (   P < 0.01  ) in these patients (median 4.45 μmol/mg creatinine) than in those with normal flow velocity waveforms (median 11.43 μmol/mg creatinine). A significant negative correlation was observed between nitrite concentrations and uterine artery resistance index, umbilical artery pulsatility index and umbilical artery pulsatility index:middle cerebral artery pulsatility index ratio.
Conclusions We conclude that placental nitric oxide is significantly associated with uteroplacental blood flow and may be important in maintaining adequate uteroplacental perfusion in intrauterine growth retarded pregnancies.