Effect of antenatal steroids (AS) on functional residual capacity and pulmonary compliance in twins

AS are known to mature lung function in the preterm infant. Traditionally, twins are treated with the same dose of AS (two 12 mg doses of Betamethasone) as singletons. However, the appropriate dose of AS for twins remains a topic of conjecture. We have reported a significantly increased functional residual capacity (FRC) and respiratory compliance (Crs) at 24 hours of age in preterm infants receiving AS versus controls (Fed Res 1995:35:224). To evaluate the effect of AS on pulmonary mechanics in twins, we measured FRC and Crs in 10 sets of twins 25 and 34 weeks of gestation (mean birth weight=1762g, GA=31.4 wks, 65% male, 80% Caucasian, 5% treated with surfactant) who had received a full course of AS (2 doses of betamethasone at least 24 hours before, but within 7 days of delivery). Twenty matched singletons (mean birth weight=1743g, GA=31.4 wks, 50% male, 70% Caucasian, 5% treated with surfactant) who had also received a full course of AS served as our comparison group. Infants who had received TRH were excluded. FRC was measured with the nitrogen washout technique within 24 hours of age, and prior to surfactant delivery, if required. A minimum of two measurements were performed with the neonate supine and quiet. Only consistent tracings initiated at end expiration and without evidence of a leak were accepted. A study was acceptable if the measurements had a coefficient of variation <10%. Crs was measured using the single breath occlusion technique (Sensormedics 2600). Values are mean ± SEM. FRC in cc/kg. Crs in ml/cm H2O/kg. 24 hrs of age 7 days of age FRC Crs FRC Crs TWINS(n=20) 28.0±1.2 1.30±0.14 28.4±1.8 1.36±0.11 SINGLETON(n=20) 28.9±1.8 1.18±0.12 31.3±2.0 1.35±0.15 p=>0.05 for all comparisons A full course of AS improves lung function to the same extent in twins as in singleton gestations. Our measurements of lung volumes and static compliance at 24 hours and 7 days of age in AS treated twins versus matched AS treated singletons support the traditional dose of AS as appropriate for twins.