Fluctuation of Urinary Level of Follicle Stimulating Substance and of Estrogen during Pregnancy

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Urinary estrogen level in various stages of human pregnancy increased after pregnant mare serum (PMS) injection. This increase in the estriol fraction was statistically significant, whereas the level of urinary FS-substance in the first and second trimesters of pregnancy rose remarkably following temporary fall after injection of estradiol benzoate. This suggests a feed-back mechanism between FSH and estrogen secretion during pregnancy.
The level of urinary FS-substance reached a peak in the third month of gestation and thereafter it fell to a relatively constant level. Later it again increased and reached the second peak in the 8th month and decreased toward the 9th month. In the 10th month the level was higher than that in the 3rd and 8th months. FS-substance contained in the placenta began to increase from the second trimester and it reached a peak in the 8th month, and then decreased in the last 2 months.
These results indicated that the FS-substance was predominantly derived from the anterior pituitary during the early months of gestation, whereas con-siderable amounts of it were delivered from the placenta at least near the end of gestation.