the chest X-ray, which demonstrates decreased lung volumes (bell-shaped chest), absence of the thymus (after about six hours), a small (0.5–1 mm), discrete, uniform infiltrate (sometimes described as a "ground glass" appearance or "diffuse airspace and interstitial opacities") that involves all lobes of the lung and air-bronchograms (i.e. the infiltrate will outline the larger airways passages, which remain air-filled). In severe cases, this becomes exaggerated until the cardiac borders become indiscernible (a 'white-out' appearance). Prevention Giving the baby's mother glucocorticoids speeds the production of surfactant. For very premature deliveries, a glucocorticoid is given without testing the fetal lung maturity. The American College of Obstetricians and Gynecologists (ACOG), Royal College of Medicine and other major organizations have recommended antenatal glucocorticoid treatment for women at risk for preterm delivery prior to 34 weeks of gestation. Multiple courses of glucocorticoid administration, compared with a single course, do not seem to increase or decrease the risk of death or neurodevelopmental disorders of the child. In pregnancies of longer than 30 weeks, the fetal lung maturity may be tested by sampling the amount of surfactant in the amniotic fluid by amniocentesis, wherein a needle is inserted through the mother's abdomen and uterus. Several tests are available that correlate with the production of surfactant. These include the lecithin-sphingomyelin ratio ("L/S ratio"), the presence of phosphatidylglycerol (PG), and, more recently, the surfactant/albumin (S/A) ratio. For the L/S ratio, if the result is less than 2:1, the fetal lungs may be deficient in surfactant. The presence of PG usually indicates fetal lung maturity. For the S/A ratio, the result is given as milligrams of surfactant per gram of protein. A S/A ratio less than 35 indicates immature lungs, between 35 and 55 is indeterminate, and greater than 55 indicates mature surfactant production (correlating with an L/S ratio of 2.2 or greater). Epidemiology Infant respiratory distress syndrome (IRDS) is the leading cause of death in premature infants. Despite only 1% of all birth complications being attributed to respiratory distress syndrome, there is a significantly higher prevalence in prematurely born babies. Incidence rates of IRDS in premature infants born at 30 weeks of gestational age (GA) are at 50%, and rise even higher to 93% for infants born prematurely at 28 weeks of gestational age or younger. IRDS is diagnosed within hours of delivery and usually leads to morbidity and mortality in preterm infants. There are many risk factors that