Background: Earlier studies suggesting an increased recurrence risk of respiratory distress syndrome (RDS) among the subsequent infants of women with a previously affected infant were based on low birth weight inclusion criteria that did not differentiate between preterm and growth-retarded infants.
Methods: We therefore carried out two cohort studies of women who delivered two singleton preterm (gestational age < 37 completed weeks) infants: 1978 to 1989 at the Royal Victoria Hospital (RVH) in Montreal and 1959 to 1966 in the United States Collaborative Perinatal Project (CPP). We compared the relative risk (RR) of the development of RDS in the second infant according to the RDS status of the first. The diagnosis of RDS was based on respiratory distress of more than 24 hours' duration and a reticulogranular pattern on a chest radiograph.
Results: The RVH study sample comprised 284 infants born to 142 women, and the CPP sample 642 infants born to 321 mothers. In the RVH cohort the crude RR of RDS in the second sibling was 3.3 (95% confidence interval = 1.0 to 15.1) in women whose first preterm infant had RDS versus those whose first preterm infant did not have RDS. In the CPP cohort the corresponding RR was 2.5 (95% confidence interval = 0.8 to 7.9). These elevated risks were not altered substantially when multiple logistic regression was used to control for potentially confounding factors known to influence the risk of RDS (gestational age, sex, route of delivery, antenatal corticosteroids, and respiratory depression of birth).
Conclusions: We conclude that preterm infants born to women with a previous preterm infant affected by RDS are at an increased risk of RDS, which suggests an important genetic (or other familial) tendency in its origin.