Interpretation of indices of fetal pulmonary maturity by gestational age

Amniotic fluid indices of fetal pulmonary maturity, including the lecithin/sphimgomyclin (L/S) ratio and quantitative saturated phosphatidylcholine (SPC), are commonly employed to determine the risk of respiratory distress syndrome (RDS) in pregnancies complicated by premature labour, ruptured membranes, or uncertain duration of gestation.  Despite consensus on the value and interpretation of results in these clinical settings, controversy remains regarding the use of routine amniocentesis and examination of amniotic fluid indices of fetal pulmonary maturity prior to repeat Caesarean section in the near or full-term gestation of reasonably certain dates.  Alternative strategies have been described which attempt to meet the goals both of minimising iatrogenic RDS and of avoiding complications of amniocentesis.  Debate has focused on the relative merits of clinical evaluation (based on early obstetric examination, firm dating of the last menstrual period, and first or mid-trimester ultrasound), compared with documentation of amniotic fluid indices of fetal pulmonary maturity1.  Since there exists no universally accepted obstetric approach to the question of routine amniocentesis prior to elective Caesarean section at term, application of principles of testing provides an additional perspective worthy of consideration in clinical decision-making. (October 1988)