136 Antenatal Steroids and Risk of Bronchopulmonary Dysplasia: A Lack of Effect or a Statistical Artifact?

Objectives: To test the hypothesis that the lack of protective effect of antenatal steroids (ANS) on bronchopulmonary dysplasia (BPD) could derive from overadjustment during analysis, caused by controlling for factors that are intermediate in the causal pathway between treatment and outcome.Methods. A cohort of infants 23 to 32 weeks of gestation, admitted to 10 tertiary-level neonatal units in Lombardy (Northern Italy) in 1999–2002, was prospectively studied; 1118 neonates out of 1314 survived to 36 weeks; 15.9% developed BPD (oxygen requirement at 36 weeks); 82% were treated with ANS.Results. In univariate analysis, ANS were not significantly protective against BPD; some intermediate factors (mechanical ventilation, greater severity of illness as measured by CRIB score, patent ductus arteriosus) were positively associated with (i.e. were risk factors for) BPD (OR=11.0, 1.46, 4.42 respectively, all P<0.001), and negatively associated with (i.e. prevented by) ANS (OR=0.58, 0.92, and 0.58 respectively, all P<0.001). In multiple logistic regression models without the above-mentioned intermediate risk factors, ANS-treated infants had a lower risk of BPD (OR 0.59; 95% CI 0.36, 0.95, P=0.03); other factors significantly associated to BPD were male sex (OR=2.07), late-onset sepsis (OR= 4.31), and birthweight (OR=0.62 for 100 g increase), all P<0.001. When also intermediate risk factors for BPD, which are prevented by ANS, were added to the model, ANS effect disappeared, thus demonstrating the existence of overadjustment.Conclusions. These results support the hypothesis that incorrect methods of analysis can obscure ANS protection against BPD. Using proper adjustment, ANS appeared to decrease the risk of BPD in this cohort.