Risk factors associated with preterm birth in the Dominican Republic: a case-control study

OBJECTIVES: This study aimed to identify the risk factors associated with preterm birth, and to determine the prevalence of preterm births in the Dominican Republic. DESIGN: Case-control study. SETTINGS: Seven National Reference Hospitals from different regions of the Dominican Republic. PARTICIPANTS: A probabilistic sampling of both cases and controls was performed with a ratio of 2.92:1, and a power analysis was performed with α=0.05, P(1)=0.5, P(2)=0.6, and β=0.08, to yield a distribution of 394 cases and 1150 controls. Estimation of gestational age was based on neonatologist reports. PRIMARY OUTCOME MEASURES: A protocol was created to obtain maternal and obstetric information. RESULTS: The main risk factors were a family history of premature births (p<0.001, OR: 14.95, 95% CI 8.50 to 26.29), previous preterm birth (p=0.005, OR: 20.00; 95% CI 12.13 to 32.96), advanced maternal age (over 35 years; p<0.001, OR: 2.21; 95% CI 1.57 to 3.09), smoking (p<0.001, OR: 6.65, 95% CI 3.13 to 13.46), drug consumption (p=0.004, OR: 2.43, 95% CI 1.37 to 4.30), premature rupture of membranes (p<0.001, OR: 2.5) and reduced attendance at prenatal consultations (95% CI 6 to 7, Z=−10.294, p<0.001). CONCLUSION: Maternal age greater than 35 years, previous preterm birth, family history of preterm births and prelabour rupture of membranes were independent risk factors for preterm birth. Adolescence, pregnancy weight gain and prenatal consultations, on the other hand, were protective factors for preterm birth. Although the prevalence of premature births in this study was 25%, this could have been biased.