THE EXCRETION OF »LABILE« OESTROGENS DURING HUMAN PREGNANCY

ABSTRACT Recently a new method of assaying the »labile oestrogens« of pregnancy urine became available as the difference between the »ammonium sulphate total«, which measures the »total (stable + labile) oestrogens« of the urine, and a »modified Brown total«, which measures its »total stable« oestrogens content. The »labile oestrogen« fraction increases during normal (uncomplicated) pregnancy, from an average of 17 per cent at 20 weeks of pregnancy to 48 per cent of the »modified Brown« total at term, or from 15 to 33 per cent of the »ammonium sulphate total« for the same time periods. Since the ketolic oestrogens form an approximately constant 15 (14–16) per cent of the total oestrogens excreted during a normal pregnancy (Hobkirk & Nilsen 1962; Hobkirk et al. 1970), this increasing percentage of total »labile« oestrogens must therefore be due to an increase in non-ketolic labile oestrogen(s). This increase in the »labile« fraction is such that it tends to compensate for the decreasing per cent of »total« oestrogen yielded by the oestrone + oestradiol fractions of the urine with progressing pregnancy. Thus the oestrone + oestradiol plus the »labile« fractions tend to fall within the range of 30 to 35 per cent of the »ammonium sulphate total«; and the oestriol fractions excreted during a normal pregnancy tend to fall within the range of 65 to 70 per cent, but may occasionally reach levels of close to 50 per cent or greater than 80 per cent, of this »total«.