Nitric oxide metabolites and preterm pregnancy complications

Intraamniotic infection may play a significant role in preterm labor and premature rupture of membranes. Synthesis of nitric oxide and its metabolites nitrite and nitrate purportedly are increased in infection. This project was designed to evaluate whether plasma or urine nitrate concentrations are increased in patients with either preterm labor or premature rupture of membranes in comparison with pregnant controls.

A total of 42 patients between 24 and 35 weeks' gestation (20 with preterm labor; 14 with premature rupture of membranes, and 8 with premature rupture of membranes and contractions) and 35 additional patients without preterm labor or premature rupture of membranes (controls) had blood and urine collected for nitrate determination. Nitrate was reduced to nitrite and quantitated with the Griess reagent.

The urine nitrate concentrations were significantly higher only in the preterm labor group compared with the control group (1.23 +/- 0.22 vs 0.67 +/- 0.05 mumol/mg creatinine, p < 0.05). The plasma nitrate level, however, was significantly higher in both the preterm labor and the premature rupture of membranes groups compared with the control group (52.47 +/- 10.11 and 40.05 +/- 5.38 mumol/L vs 16.29 +/- 2.89 mumol/L, p < 0.05). However, the concentrations of nitrate in the urine or plasma did not correlate with time from admission to delivery (p > 0.2). Finally, the presence of positive cervical or urine cultures, a clinical examination consistent with chorioamnionitis, or a maternal temperature > 100.4 degrees F was not associated with higher levels of nitrates in this small series of patients.

Patients with preterm labor or premature rupture of membranes do have increased nitrate concentrations; however, this increased concentration is not predictive of impending delivery but may indicate that a subclinical infectious process is occurring.