SERUM NITRITES PREDICT THE RESPONSE TO PROSTAGLANDIN-INDUCED DELIVERYAT TERM

OBJECTIVE: To evaluate whether the clinical response to prostaglandin- induced labor is modulated by nitric oxide (NO) activity. METHODS: Fif ty-two cases of nulliparous women at term who delivered vaginally afte r prostaglandin E (PGE) induction of labor were enrolled. The inductio n was required mainly for amniotic fluid reduction or late-onset gesta tional hypertension. Either intracervical (0.5 mg) or vaginal (2.0 mg) PGE was administered every 12 hours, according to the Bishop score. A fter the third PGE application, in absence of labor onset, intravenous oxytocin was used. Nitrites/nitrates (NOx) serum levels were used as a marker of NO activity. They were measured just before the start of i nduction by using an enzymatic reduction and then a colorimetric evalu ation. Time to delivery from the first PGE application was the main ou tcome variable. RESULTS: Time to delivery ranged from 4 to 62 hours (m edian: 15.5). Nitrites/nitrates levels were unaffected by both gestati onal age, Bishop score at entry, indication allowing labor-induction, fetal position, and birth weight. In a multiple regression analysis in cluding the previous factors, NOx levels significantly explained 33.9% of the variance of the time delivery. Indeed, patients delivering wit hin 15 hours (26.4 +/- 6.9) showed NOx levels significantly lower than in patients delivering after more than 15 hours (39.5 +/- 16.4) from the first PGE application. CONCLUSIONS: A reduced level of NOx is asso ciated with a prompt clinical response to PGE-induced labor. Provided we do not know the origin of NOx in the general circulation, these dat a indicate NOx levels as predictors of the response to PGE-induced del ivery at term and support the hypothesis that labor onset is modulated by the endogenous NO activity. Copyright (C) 1998 by the Society for Gynecologic Investigation.