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Chapter 18 - Imprinting
from Section 6: - Genetics
- By Sayeda Abu-Amero, Gudrun E. Moore
Edited by Robert Pijnenborg, Ivo Brosens, Roberto Romero
Book:

Placental Bed Disorders

Published online:

06 July 2010

Print publication:

03 June 2010, pp 183-194
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Summary

This chapter reviews the roles and distribution of O2 inside the early human gestational sac and its impact on our understanding of the physiology of O2 metabolism by the fetus during the first and early second trimesters of pregnancy. The mammalian fetus is exposed to major fluctuations in O2 concentration from conception to delivery. The first trimester gestational sac has additional barriers to materno-fetal exchange compared to the definitive placenta of the second and third trimesters of pregnancy. Ample dilation of the uteroplacental circulation together with rapid villous angiogenesis are the key factors necessary to adequate placental development and function and subsequent fetal growth. Overall the data have confirmed that the human placenta is not truly hemochorial until the end of the first trimester. Rather it is deciduochorial, being supported by tissue fluids and endometrial secretions.