<prompt> Foetal lung maturity is assessed by ___LS ratioBillirubin content of amniotic fluidUltrasoundAmniocentesis  <response>: The presence of surfactant in amniotic fluid is evident of fetal lung maturity. LS ratio determines the relative concentration of surfactant. LS ratio is lecithin to sphingomyelin ratio and should be more than 2. There is an increased risk of respiratory distress syndrome when this ratio is less than 2. Reference : page 516 Textbook of Obstetrics Sheila Balakrishnan 2nd edition 