Amniotic fluid is obtained by amniocentesis at 34 weeks gestation. The lecithin-to-sphingomyelin (L/S) ratio is reported as 3.0. This finding indicates:

• A Immature lungs with high probability of respiratory distress syndrome
• B Chronic intrauterine hypoxia requiring immediate delivery
• C Fetal renal maturity with adequate surfactant-independent lung development
• D Mature fetal lungs with low risk of respiratory distress syndrome ✓

Explanation

Surfactant phospholipids rise steeply after about 32 weeks, and an L/S ratio of 2.0 or more conventionally predicts lung maturity with a very low incidence of RDS. A ratio of 3.0 therefore indicates mature lungs and a low risk of respiratory distress. Sphingomyelin concentration stays roughly constant while lecithin rises, so the ratio tracks surfactant adequacy rather than renal maturity or hypoxia.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.