- Abstract The purpose of this study was to examine whether changes in estrogen and progesterone levels observed during normal pregnancy influence blood glutamate levels. One-hundred and sixteen pregnant women were divided into three groups based on gestational age: group 1 included women in their first trimester, group 2 included women in their second trimester, and group 3 included women in their third trimester. A single venous blood sample was collected and analyzed for concentrations of estrogen, progesterone, glutamate-pyruvate transaminase (GPT), glutamate-oxaloacetate transaminase (GOT), and glutamate. Concentrations of blood glutamate were significantly lower during the second trimester (p < 0.001) and third trimester (p < 0.001). Blood glutamate levels were inversely correlated with levels of estrogen and progesterone throughout pregnancy (p < 0.001). Levels of GOT and GPT remained stable during the course of pregnancy, apart from a moderate reduction in GPT during the third trimester. Increases in estrogen and progesterone levels during advanced stages of pregnancy were inversely correlated with maternal blood glutamate concentrations. Once a maximal blood glutamate-reducing effect was achieved, any additional estrogen and progesterone had a negligible effect on blood glutamate. This study demonstrates the glutamate-reducing effects of estrogen and progesterone, which is most likely not mediated by a GOT/GPT conversion mechanism.