The influence of maternal fat metabolism on fetal carnitine levels.

Carnitine facilitates fatty acid transport across mitochondrial membranes, playing a key role in fatty acid oxidation and ketogenesis. To investigate the mechanism by which carnitine and its esters are supplied to the fetus, we measured free carnitine (FC) and acyl carnitine (AC) in amniotic fluid during late pregnancy, and FC, AC and beta-hydroxybutyrate (beta-OHB) in maternal and fetal plasma at vaginal term delivery. Amniotic fluid AC levels were elevated in pregnancies complicated by toxemia and diabetes mellitus, possibly reflecting placental transfer during abnormal fat catabolism. Maternal plasma levels of beta-OHB and AC were elevated and positively correlated at vaginal delivery, indicating enhanced fatty acid utilization. The positive correlation between maternal and fetal FC, AC and beta-OHB plasma levels suggests placental transfer. The maternal-fetal concentration gradient was descending for beta-OHB and AC and ascending for FC. No umbilical venous-arterial gradient for AF and beta-OHB was found, suggesting that the fetus does not utilize substantial amounts of either substance. The results demonstrate that fetal FC and AC levels are influenced by changes in maternal fat metabolism.