Maternal or umblical venous levels of nitrite/nitrate during pregnancy and at delivery.

OBJECTIVE

This study was intended to measure serum concentrations of nitrite plus nitrate as an index of nitric oxide synthesis, in the maternal vein during pregnancy, just after a spontaneous delivery and at the puerperium, and at an elective cesarean section, and in the umblical vein and artery.

METHODS

Maternal venous sera, and umblical venous and arterial sera were collected, and serum concentrations of nitrite/nitrate were measured by an automated procedure based on the Greiss reaction after reduction of nitrate to nitrite.

RESULTS

Compared to a serum concentration of nitrite/nitrate at the first trimester (12-13 weeks of pregnancy), a serum concentration of nitrite/nitrate slightly increased at the second trimester (27-28 weeks), and became maximal at the third trimester (35-36 weeks), followed by a significant decrease near the term (38-40 weeks). A serum concentration of nitrite/nitrate slightly increased just after a spontaneous delivery with labor pains, and at the puerperium to levels slightly more than that at the first trimester. Serum concentrations of nitrite/nitrate in the umblical vein and artery did not differ. They were significantly higher than a serum concentration of nitrite/nitrate in the maternal vein just after a spontaneous delivery with labor pains but not at an elective cesarean section without labor pains.

CONCLUSION

A decrease in maternal serum levels of nitrite/nitrate near term may support a hypothesis that NO is one of factors responsible for the maintenance of uterine quiescence during pregnancy. Moreover, the present results suggest that NO plays some role in the feto-placental circulation during a spontaneous delivery.