Background & Aims:Preterm delivery is an important determinant of prenatal period that happened in 5-12% of pregnancies. Studies have shown that one of the risk factors is sleep and sleep related disorder like sleep apnea .This study was conducted to determine the relationship between sleep apnea (OSA) on spontaneous preterm birth in Ardabil city.

Materials & Methods: We performed an analytical cohort study, screening 234 pregnant women in 28-32 weeks for OSA symptoms. The multistage sampling methods were used and subjects were enrolled into two groups (118 subjects without sleep apnea and 116 subjects with sleep apnea), then, followed for the occurrence of preterm delivery .The data were collected using demographic and obstetrics questionnaire, Berlin questionnaires and Epworth sleepiness scale, and were analyzed with SPSS.

Result: Accordingly, 28 (65.1%) subjects with sleep apnea and 15 (47.2%) in the group without sleep apnea had preterm birth and there was a significant difference between groups (p<0.03). OSA was associated with an increased risk of PTB (OR= 2.08; 95% CI, 1.04–4.16).An important association was found between preterm birth and variables such as snoring frequency, sleep time&ge;8 hours  (p<0.05).

Conclusion: Pregnancies complicated by OSA are at increased risk for preterm birth.