Decreased plasma tryptophan in pregnancy

To examine levels of serum tryptophan and its degradation product kynurenine in uncomplicated pregnancy, according to the week of pregnancy and the concentrations of neopterin. Plasma was analyzed from 45 healthy pregnant women (15 in each trimester), 15 healthy puerperas, and 20 nonpregnant controls. Tryptophan and kynurenine were measured by reverse-phase, high-performance liquid chromatography, and neopterin by radioimmunoassay. In healthy pregnant women, tryptophan values decreased (median first trimester: 72 μmol/L; second trimester: 51 μmol/L; third trimester: 46 μmol/L; P < .001) in a manner correlated with the duration of pregnancy (Spearman rank correlation coefficient r s = −0.771, P < .001) and normalized in the puerperium (median 60 μmol/L). No change in kynurenine, a tryptophan degradation product, was observed, but the ratio of kynurenine to tryptophan increased during pregnancy and correlated positively with gestational age ( r s = 0.714, P < .001). In addition, an inverse correlation existed between neopterin and tryptophan concentrations ( r s = −0.566, P < .001), as well as a positive one between neopterin and the kynurenine to tryptophan ratio ( r s = 0.660, P < .001). Tryptophan levels decrease during normal pregnancy and the decrease may be related to immune activation phenomena.