Effects of oral l-arginine on the pulsatility indices of umbilical artery and middle cerebral artery in preterm labor

ObjectiveThe objective of the study was the estimation of the influence of oral supplementation with low-dose l-arginine on feto-placental circulation in women with threatened preterm labor.Study designOral administration of 3 g of l-arginine daily or placebo as a supplement to standard tocolytic therapy was tried in 70 women with threatened preterm delivery, randomly assigned to the l-arginine (n = 37) or placebo (n = 33) groups. Twenty-five and 20 completed the study, respectively. Doppler velocimetry of pulsatility indices (PI) of the umbilical (UA) and middle cerebral (MCA) arteries as well as pregnancy outcome and biochemical markers of nitric oxide synthesis (plasma amino acid and nitrite/nitrate levels, as well as 24 h nitrite/nitrate excretion with urine) were estimated.ResultsStarting from the second week of therapy, the UA PI values were significantly lower in the l-arginine group than in the placebo group. Moreover, treatment with l-arginine caused a significant increase in MCA PI and cerebro-placental ratio (CPR) values. The changes in feto-placental circulation in the l-arginine group were not associated with any signs of increased nitric oxide synthesis.ConclusionOral supplementation with low doses of l-arginine changed feto-placental blood flow distribution in patients with threatened preterm labor. The exact mechanism of l-arginine action on feto-placental circulation requires further investigation.