Plasma carnitine and renal-carnitine clearance during pregnancy.

This study assessed the time course of decrease in plasma carnitine during pregnancy and compared the renal clearance of carnitine during late pregnancy with nonpregnant women. As early as the 8th wk of pregnancy, the mean (+/- SD) value of total plasma-carnitine concentration in 19 women was significantly decreased from 39.0 +/- 6.3 to 32.8 +/- 4.6 mumol/l and the values continued to fall to 17.3 mumol/l by the 36th wk. The pattern was due to a fall in free-carnitine level; acylcarnitine remained unchanged. In 12 other women examined during late pregnancy, the renal clearance of acylcarnitine was significantly higher than in nonpregnant women, 53.9 +/- 29.4 versus 13.3 +/- 3.0 ml/min, in contrast to free carnitine, 3.5 +/- 2.8 versus 2.8 +/- 1.9 ml/min. Urinary excretion of carnitine (expressed per mol creatinine) did not differ between the two groups. Pregnant women showed sustained excretion of carnitine in the presence of low plasma-carnitine concentrations.