Preterm birth (i.e,. birth before 37 completed weeks’ gestation) is the most important cause of perinatal mortality (Berkowitz et al., 1993); approximately 13 million infants are born preterm worldwide each year (Keirse, 1995). Various studies have estimated that preterm birth accounts for between 69% and 85% of early neonatal deaths that were not caused by lethal congenital malformations, and it is also a major determinant of long-term morbidity (Berkowitz et al., 1993). Any treatment which prolongs the length of gestation could have a profound effect on neonatal mortality and morbidity. This has directed our attention to undergo this study to compare the effect of β-mimetics (the standard treatment for tocolysis) with NO donors as nitroglycerine, a drug widely used in cardiology but what is new is it use in tocolysis.