Antenatal steroids have been clinically for 25 years to reduce the risk of respiratory distress syndrome (RDS), the major cause of death among newborn infants. However, this therapy is grossly underutilized because it is only 50 percent effective in reducing the risk of RDS, making it a difficult therapy to control. This laboratory has discovered that maternal serum estriol (E3) indicates whether or not the fetus has responded to the drug before birth, providing an objective means of managing these high risk pregnancies for the first time. In Phase I this observational study will be expanded at the University of Maryland and at 5 other regional perinatal centers nationally to validate the clinical use of this test using standard radioimmunoassay (RIA) technology. Maternal estriol determined by RIA will then be used to validate estriol measured by a quantitative enzyme-linked immunosorbent assay (EIA), which is a more accessible and cost-effective technology. Validation of this test using EIA will facilitate its reduction to practice and commercialization. In addition, biologic validation of this test will be provided by correlating it with the effects of antenatal steroids on both fetal adrenal DHA in cord blood and on lung surfactant in amniotic fluid and neonatal RDS. In Phase II more patient data will be collected on this complex patient population in order to develop a "bedside" qualitative EIA specifically for this purpose. This new test may provide a breakthrough for obstetric management of preterm pregnancies treated with antenatal steroids.