Sir.—I was intrigued by Dr. Shaw's letter concerning the cause of hyaline membrane disease, which appeared in the August issue of the Journal (128:259, 1974). He has echoed many of my thoughts and has tried to stress the importance of (1) the aspirate and (2) vaginal compression during delivery.
It is true that surfactant deficiency may be a factor in this condition, but there are other factors also. The lecithin/sphingomyelin ratio is only a measure of lung maturity, but not a reliable predictor of the respiratory distress syndrome.1-3 As Dr. Shaw has pointed out, vaginal compression squeezes fluid out of the lung during delivery, and I believe that it may serve an even more important function, that is to "prevent aspiration" during the infant's passage down the birth canal. This compression is absent in cesarean section.
I have previously suggested that aspiration of amniotic fluid and its contents
PENDER CB. Cause of Respiratory Distress Syndrome. Am J Dis Child. 1975;129(2):260. doi:10.1001/archpedi.1975.02120390084025