You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is The concentration of lecithin relative to sphingomyelin begins to rise in the following week: and explain in detail?
Before 34 weeks, lecithin and sphingomyelin are present in amnionic fluid in similar concentrations. At 32 to 34 weeks, the concentration of lecithin relative to sphingomyelin begins to rise. Dipalmitoylphosphatidylcholine--DPPC, that is, lecithin--along with phosphatidylinositol and especially phosphatidylglycerol is an impoant component of the surface-active layer that prevents alveolar collapse. Ref: Leveno K.J., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 29. Diseases and Injuries of the Fetus and Newborn. In K.J. Leveno, J.C. Hauth, D.J. Rouse, C.Y. Spong (Eds), Williams Obstetrics, 23e.