Fetal respiration: quantitative measurements of amnionic fluid inspired near term by human and rhesus fetuses.

Observations reported now on primate pregnancies, human and rhesus, combined with earlier studies from this laboratory, demonstrate that normally appreciable volumes of amnionic fluid are inhaled and presumably exhaled throughout much of pregnancy. Through use of isotope-labeled red cells and porcelain microspheres placed at varying times in the amnionic sac, as well as fetal squames already present, it has been shown conclusively that inhalation of amnionic fluid is not necessarily a pathologic event. The volumes of amnionic fluid inhaled per 24 hours by human and rhesus fetuses late in pregnancy were remarkably similar, amounting on the average to at least 200 ml per kilogram. These observations confirm the much earlier qualitative studies of some others that previously had generally been discounted by many fetal physiologists.