BackgroundPreterm birth is one of the key causes of morbidity and mortality among neonates in low-income countries. In Rwanda, at least 35,000 babies are born prematurely each year, and 2600 children under the age of five die due to direct complications of prematurity each year. A limited number of studies have been conducted locally, many of which are not nationally representative. Thus, this study determined the prevalence as well as the maternal, obstetric, and gynecological factors associated with preterm birth in Rwanda at the national level.MethodsA longitudinal cohort study was conducted from July 2020 to July 2021 among first-trimester pregnant women. A total of 817 women from 30 health facilities in 10 districts were included in the analysis. A pre-tested questionnaire was used to collect data. In addition, medical records were reviewed to extract relevant data. Ultrasound examination was used to assess and confirm gestational age on recruitment. A multivariable logistic regression analysis was performed to determine the independent maternal, obstetric, and gynecological factors associated with preterm birth.ResultsThe prevalence of preterm births was 13.8%. Older maternal age- 35 to 49 years [Adjusted odds ratio (AOR) = 2.00; 95% Confidence Interval (CI) = 1.13–3.53)], secondhand smoke exposure during pregnancy (AOR = 1.91; 95% CI = 1.04–3.51), a history of abortion (AOR = 1.89; 95% CI = 1.13–3.15), premature membrane rupture (AOR = 9.30; 95% CI = 3.18–27.16), and hypertension during pregnancy (AOR = 4.40; 95% CI = 1.18–16.42) were identified as independent risk factors for preterm birth.ConclusionPreterm birth remains a significant public health issue in Rwanda. The associated risk factors for preterm birth were advanced maternal age, secondhand smoke, hypertension, history of abortion, and preterm membrane rupture. This study therefore recommends routine antenatal screening to identify and closely follow-up of those high-risk groups, in order to avoid the short- and long-term effects of preterm birth.