[Development of the placenta and utero-placental circulation from the morphologic and functional viewpoint]

Abstract

All requirements of the conceptus, i.e. the fetus and the placenta are distributed by the maternal blood via the utero-placental vessels. Fetus and placenta need varying amounts of oxygen and nutrients at different stages of pregnancy. In the first half of pregnancy, the placenta, besides growth and development, fulfills the function of an endocrine gland whilst the nutrient supply of the fetus is of minor importance. In the second part of pregnancy, the placenta differentiates into an organ for exchange of gases and nutrients. Placental development may be divided into three stages: Implantation, growth and maturation. In the first half of pregnancy, the placental growth precedes the major fetal growth spurt, whereas, in the second half, the weight ratio placenta: fetus shifts in favour of the fetus and reaches 1:7 to 1:10 at the end of pregnancy. Growth and development of the placenta is the basis for fetal growth and it is not surprising that the weight ratio of the placenta and the newborn is positively correlated at the end of pregnancy. From the morphological point of view the development of the utero-placental circulation is characterized by a loss of the muscular elements in the wall of the peripheral parts of the spiral arteries supplying the endometrium and the intervillous space. These morphological changes functionally correlate with a reduction of resistance in the peripheral vessels. This can be visualized even doppler-sonographically as a reduction of pulsatility in the radial arteries.(ABSTRACT TRUNCATED AT 250 WORDS)