Abstract 337 Poster Session I, Saturday, 5/1 (poster 143)

Background: Nitric Oxide (NO) is generated in the human feto-placental circulation and the myometrium, where it contributes to the control of basal vascular and uterine tone. iNOs may decrease with advancing gestation. However, the levels of nitric oxide at different gestational ages and the possible association of decreasing NO concentrations in fetal circulation with labor have not been well established. Objective: The aim of this ongoing study is to determine levels of nitric oxide and its metabolites in cord venous blood of pregnancies at different gestational ages at time of delivery and describe the relation of nitric oxid production to gestational age and to the presence of labor. Methods: Cord venous blood was collected soon after cord clamping, centrifuged at 2500 rpm for 10 min., frozen at -80°; stored for 30-60 days. Nitric Oxide levels were measured using the Sievers 280 NO Analyzer (Boulder, CO) using vanadium (III) chloride to reduce serum nitrate/nitrite to nitric oxide. Subsequently nitric oxide was measured by chemiluminescence. Data was compared by paired Student t-test.

Results: To date we have studies 47 term infants (29 delivered by normal spontaneous vaginal delivery [NSVD]; 13 delivered by elective C-section, without preceding labor, and 5 delivered by C-section after labor). All subjects had uncomplicated pregnancies, deliveries and neonatal courses. (Table)

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Conclusions: The results of this ongoing study show that in term human gestation nitric oxide production is lower in the presence of labor. While factors that may participate in this association deserve further study, we speculate that a nitric oxide production threshold is related to the initiation at term