Betamethasone and Severity of Hyaline Membrane Disease in the Newborn Premature

β-Mhyalines is a prospective multicentric non interventional study. One hundred fifty pregnant women at risk of premature delivery, in the framework of Hyaline Membrane Disease of the neonate, will receive 2 intramuscular injections of Celesten (betamethasone) at 24 hours interval. Plasma samples will be collected: 2 in the mother before delivery, one maternal and one cord samples at delivery. Concentrations will be measured and analyzed using a population approach. A ratio between neonatal and maternal exposure will be calculated to represent placental transfer. The effect of covariates (genetic polymorphism for CYP3A4, CYP3A5, P-glycoprotein…, and others variables as gestational age, bodyweight at birth, apgar score, co-medication, maternal disease) will be tested to explain the variability of placental transfer. The relationship between placental transfer and the occurrence and severity of the Hyaline Membrane Disease will then be study, in order to target betamethasone maternal concentration and thus to optimize the antenatal dose to administer to the mother in the framework of Hyaline Membrane Disease.