Bilirubin‐IX α and ‐IX β pigments, coproporphyrins and bile acids in meconium and stools from full‐term and preterm neonates during the first month of life

Individual bilirubin pigments in the excreta were quantitated by newly developed methods. In meconium, bilirubin‐IX β predominated, whereas bilirubin‐IX γ and ‐IX δ remained undetectable. The daily excretion of bilirubin‐IX α plus ‐IX β was 0.03–1.00 and 0.04–2.00 μmoles kg 1 of birthweight in preterm and full‐term infants, respectively. The ratio of bilirubin‐IX α to ‐ IX β in meconium was 0.25 ± 0.34, 0.32 ± 0.30 and 0.46 ± 0.55 in newborns of gestational ages below 30, from 31 to 36 and above 36 wk, respectively. The predominance of bilirubin‐IX β disappeared within the first week in those with gestational age ± 31 wk but more slowly in the very preterm group. The ratio of monoconjugated to diconjugated bilirubin‐IX α was 4 to 5 in full‐term infants, whereas this ratio was only reached after 1 mo in preterm infants. The ratio of glucuronide or glucoside to xyloside varied widely, independent of gestational age. No correlation between faecal UCB‐IX α and β ‐glucuronidase was observed. The daily coproporphyrin excretion fell from a median of 500 μg on day 1 to below 20 μg from day 7 onwards; this decrease correlated with that of bilirubin‐IX β . The daily 3 α ‐hydroxylated bile acid loss in the excreta was two‐ to fivefold higher than in the adult; this, together with the higher neonatal serum levels (12–90 nmoles ml ‐1 ), indicates an immature intestinal reabsorption and an enhanced bile acid synthesis. Conclusion : Both zinc coproporphyrin and bilirubin‐IX β are characteristic compounds of human meconium, diconjugated bilirubin‐IX α is low or absent in meconium of very preterm infants, and faecal and serum bile acids are high.