Perinatal bile acid metabolism: analysis of urinary bile acids in pregnant women and newborns.

The metabolism of bile acids in 30 pregnant women was evaluated by analyzing the urinary composition of bile acids during late gestation (weeks 30-41) and again in these women and their newborn infants during the first week after delivery. The levels of individual bile acids were determined by gas chromatography-mass spectrometry after solvolysis and hydrolysis of bile acid conjugates. The mean total bile acid/creatinine ratio in pregnant women decreased from 1.22 micromol/mmol creatinine at 30-32 weeks of gestation to 0.15 micromol/mmol creatinine at 6-7 days after delivery. The mean percentage of 1beta-hydroxylated bile acids peaked at 27% at 3-4 days after delivery. In newborn infants, the mean total bile acid/creatinine ratio rapidly increased from 3.39 micromol/mmol creatinine at birth to 54.33 micromol/mmol creatinine at 7 days. During this period, large amounts (40-50%) of unsaturated ketonic bile acids, especially 7alpha,12alpha-dihydroxy-3-oxo-5beta-chol-1-en-24-oic acid and 7alpha,12alpha-dihydroxy-3-oxo-4-cholen-24-oic acid, were observed in the infants' urine. These data suggest that, during the perinatal period, the formation of polyhydroxylated and unsaturated ketonic bile acids probably represents a mechanism for the excretion of bile salts, and that the metabolism of bile acids in both the mother and the infant changes significantly after birth.