Blood glucose and oxygen tension levels in small-for-gestational-age fetuses.

Blood glucose and oxygen tension levels were measured in umbilical venous and arterial samples obtained by cordocentesis from 63 small-for-gestational-age fetuses. Reference ranges for these parameters were established by measurement of blood glucose (n = 122) and oxygen tension (n = 189) levels in appropriate-for-gestational-age fetuses that were undergoing cordocentesis in the prenatal diagnosis of congenital abnormalities. The fetuses were subsequently found to be unaffected by the condition investigated. In the small-for-gestational-age fetuses, the maternal-to-fetal blood glucose concentration gradients for the umbilical vein and artery correlated significantly with the degree of fetal hypoxia but not with the degree of fetal smallness. Furthermore, there was no significant difference in the relationship of maternal and fetal blood glucose concentration gradient and hypoxia between the umbilical venous and arterial samples, which suggests that the major cause of hypoglycemia in small-for-gestational-age fetuses is reduced supply rather than increased fetal consumption or decreased endogenous production of glucose.