Uterine oxygen supply and fetal health.

For nearly 300 years it has been recognized that the maternal circulation is essential for the successful accomplishment of mammalian pregnancy. William Harvey, in his De Generatione Animalium, which was published in 1651, stated his belief that the umbilical vessels carried (rather than blood) a whitish humour which served as food for the fetus.' Some of his contemporaries were still arguing about whether the fetus is alive before birth because it has no air to breathe. However, 50 years later John Ray, who helped to establish in England what we now call the science of biology, stated the modern view in his book called The Wisdom of God Manifested in the Works of the Creation.! Ray said, Against what we have said of the necessity of the Air for the maintenance of the Vital Flame, it may be objected, That the Foetus in the Womb lives, its Heart pulses and its Blood circulates; and yet it draws in no Air, neither hath the Air any access to it. To which I answer, That it doth receive Air, so much as is sufficient for it in its present state, from the maternal Blood by the Placenta. .....I say then, That the chief Use of the Circulation of the Blood thro' the Cotyledones of a Calf in the Womb, (which I have often dissected) and by Analogy thro' the Placenta . . . in an Human Foetus, seems to be the Impregnation of the Blood with Air, for the feeding of the Vital Flame. In more current scientific terms, the maternal and fetal circulations serve, along with the placenta, as living links in a complex chain that carries oxygen from the external environment to the fetal cells of humans and of most other mammals. The systematic study of the links and their relationships was begun by Barcroft' and is being systematically extended by a large number of investigators, many of whom were trained and inspired by Donald H. Barron. A review of this chain of oxygen supply will serve as a basis for some quantitative estimates of the importance and magnitude of each of its links, and for considering the evidence that maternal heart disease is a handicap to conception, pregnancy, delivery, and the survival of the new organism.