Patients with pregnancies between 26 and 36 6/7 weeks of pregnancy. Before the birth, a sample of amniotic fluid was taken and analyzed using optical density at 650nm. A value above 0.15 was considered an indication of fetal lung maturity.

A sample of amniotic fluid was taken before the birth of fetus between 26 and 36 6/7 weeks of pregnancy.

Diagnosis of Respiratory Distress Syndrome in the neonatal period. The diagnosis was made by the neonatologist in charge (using clinical and radiological parameters).