The fetal concentrating index as a gestational age-independent measure of placental dysfunction in intrauterine growth retardation.

In previous work we have shown, using cordocentesis to obtain fetal blood, that fetuses with intrauterine growth retardation are hypoxic and suffer from in utero starvation of nutrients. In this study we have developed gestational age curves for fetal blood amino acids and carnitine that now allow the development of a new parameter, the fetal concentrating index, which is the numeric mean of the fetal/maternal ratio of six essential and nonessential concentrated amino acids. Our data have shown that this index does not vary with gestation in either normal pregnancies (1.83 +/- 0.42, mean +/- SD) or pregnancies with intrauterine growth retardation (1.46 +/- 0.38), but the index is markedly reduced in intrauterine growth retardation (p less than 0.001). These results suggest that, because cordocentesis has become very safe in experienced hands, cordocentesis to obtain the fetal concentrating index might ethically be obtained in cases of fetuses at risk for intrauterine growth retardation, to devise strategies for intervention before the onset of severe hypoxia and morphometric changes.