Objective: To examine levels of serum tryptophan and its degradation p
roduct kynurenine in uncomplicated pregnancy, according to the week of
pregnancy and the concentrations of neopterin. Methods: Plasma was an
alyzed from 45 healthy pregnant women (15 in each trimester), 15 healt
hy puerperas, and 20 nonpregnant controls. Tryptophan and kynurenine w
ere measured by reverse-phase, high-performance liquid chromatography,
and neopterin by radioimmunoassay. Results: In healthy pregnant women
, tryptophan values decreased (median first trimester: 72 mu mol/L; se
cond trimester: 51 mu mol/L; third trimester: 46 mu mol/L; P < .001) i
n a manner correlated with the duration of pregnancy (Spearman rank co
rrelation coefficient r(s) = -0.771, P < .001) and normalized in the p
uerperium (median 60 mu mol/L). No change in kynurenine, a tryptophan
degradation product, was observed, but the ratio of kynurenine to tryp
tophan increased during pregnancy and correlated positively with gesta
tional age (r(s) = 0.714, P < .001). In addition, an inverse correlati
on existed between neopterin and tryptophan concentrations (r(s) = -0.
566, P < .001), as well as a positive one between neopterin and the ky
nurenine to tryptophan ratio (r(s) = 0.660, P < .001). Conclusion: Try
ptophan levels decrease during normal pregnancy and the decrease may b
e related to immune activation phenomena.