Decreased plasma tryptophan in pregnancy.

OBJECTIVE

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.

METHODS

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.

RESULTS

In healthy pregnant women, tryptophan values decreased (median first trimester: 72 mumol/L; second trimester: 51 mumol/L; third trimester: 46 mumol/L; P < .001) in a manner correlated with the duration of pregnancy (Spearman rank correlation coefficient ra = -0.771, P < .001) and normalized in the puerperium (median 60 mumol/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 (ra = 0.714, P < .001). In addition, an inverse correlation existed between neopterin and tryptophan concentrations (ra = -0.566, P < .001), as well as a positive one between neopterin and the kynurenine to tryptophan ratio (ra = 0.660, P < .001).

CONCLUSION

Tryptophan levels decrease during normal pregnancy and the decrease may be related to immune activation phenomena.