Quantitative changes in steroid and peptide hormones in the maternal-fetoplacental system between the 28th-40th weeks of pregnancy

The role of steroid and peptide hormones in the maintenance of pregnancy and in the onset of labour was investigated in the maternal-fetoplacental system between the 28th-40th weeks of pregnancy. The data of 151 pregnant women and 108 newborns was processed, and a total of 2385 samples was studied by RIA. Results showed that between the 28th-40th week there is an increase in the prolactin level of the umbilical arterial and venous blood with a parallel increase in the cortisol level of umbilical arterial blood and a fall in the progesterone level of umbilical arterial and venous blood which between the 36th and 40th week results in a rise of the oestradiol/progesterone quotient. At the same time the oestradiol concentration rises in the maternal circulation and in case of premature labour the oestradiol/progesterone quotient attains values twice as high as those found in normal pregnancies. The alteration of the hormonal environment expedites the predominance of the mechanisms stimulating the activity of the myometrium. The hormone values in the umbilical artery and vein characteristically differ from those of the maternal serum. Thus, it may be assumed that the fetus, though being in close communication with the maternal organism, is capable of independently maintaining its hormonal environment. The results indicate that the fetus or more accurately the fetoplacental unit plays a significant part in the maintenance of pregnancy and in the initiation of labour than it has been assumed previously.