Background: Preterm birth is a leading cause of neonatal morbidity and mortality worldwide, especially in women with a history of preterm birth. Vaginal progesterone has been shown to reduce the risk of preterm birth in this population. Moreover, N-acetylcysteine, known for its antioxidant and anti-inflammatory properties, is being investigated as a potential adjunct therapy to further enhance the protective effects of progesterone.
The aim of the work: The present study aimed to evaluate the efficacy of a combination of vaginal progesterone and N-acetylcysteine compared to vaginal progesterone alone in preventing preterm birth in pregnant women with a history of preterm delivery.  
Patients and Methods: A randomized controlled trial was conducted involving a total of 70 pregnant women with a history of preterm birth. Participants were divided into two groups: one receiving vaginal progesterone and N-acetylcysteine, and the other receiving vaginal progesterone alone. The primary outcome measure was the rate of preterm birth [<37 weeks gestation] in each group.
Results: Preliminary results demonstrated a lower rate of preterm birth in the group receiving the combination therapy compared to those receiving progesterone alone, but without statistically significant difference [p = 0.212].
Conclusion: The combination of vaginal progesterone and N-acetyl-cysteine shows promising results in preventing preterm birth in pregnant women with a history of preterm delivery. Further research is warranted to confirm these findings and explore the underlying mechanisms of this combined therapy for better maternal and neonatal outcomes.