Pulmonary excretion of carbon monoxide in the human infant as an index of bilirubin production

A total of 45 infants, including 20 appropriate-size-for-gestational-age infants (AGAs), 19 large-size-for-gestational-age infants (LGAs) and 6 infants of diabetic mothers (IDMs), had determinations of their pulmonary excretion rate of carbon monoxide (Ve_CO) in the first postnatal week as an index of bilirubin production. We calculated a ratio (Rw) of birth weight to ideal weight (50th percentile for gestational age) as a relative measure of infant size. We also measured maternal glycosylated hemoglobin (Hb A_Ic) in the postpartum period as a reflection of the time-integrated blood glucose level over the weeks preceding delivery. Mean values for maternal Hb A_Ic in the postpartum period, infant Rw, and Ve_CO were all significantly increased for the LGAs and IDMs compared to the normal AGAs. Nine LGAs had mothers whose Hb A_Ic levels were >2 S.D. higher than the mean Hb A_Ic level for mothers of normal AGAs. The infants whose mothers had the highest Hb A_Ic levels were not always the ones with the highest bilirubin production rates. These findings suggest that maternal Hb A_Ic in the postpartum period, infant size, and bilirubin production are associated phenomena, but that a postpartum time-integrated measure of blood glucose level over the weeks preceding parturition may not reflect changes in other associated factors which can affect infant erythropoiesis. The LGAs are not a homogeneous group, and some may have mothers with missed abnormalities of gestational glucose metaoblism.This investigation was supported in part by grants from the General Clinical Research Program of the Division of Research Resources, National Institutes of Health (RR-00081), the Thrasher Research Fund, the United States Public Health Services (AM-25603), the National Institutes of Health (HD-14426), and by the National Institutes of Health Biomedical Research Support Grant (5S01RR05583)