Maternal and fetal levels of methionine and homocysteine in early human pregnancy.

OBJECTIVE To investigate methionine metabolism during normal human embryonic development by measuring levels of methionine and total homocysteine in samples of maternal serum, extra-embryonic coelomic fluid, and amniotic fluid. DESIGN Cross-sectional observational study. SETTING Collaboration between St Bartholomew's Hospital, London, and the University Hospital of Nijmegen in The Netherlands. PARTICIPANTS Twenty-three women with uncomplicated pregnancies between 8 and 12 weeks of gestation before surgical termination of an ultrasonographically normal fetus. METHODS Maternal serum samples were collected prior to surgery. Samples of extra-embryonic fluid and amniotic fluids were obtained by transvaginal ultrasound-guided coelocentesis and amniocentesis. Methionine was measured using an amino acid analyser and total homocysteine by high performance liquid chromatography. RESULTS Levels of methionine were four times higher in extra-embryonic coelomic fluid and twice as high in amniotic fluid compared with maternal serum. In contrast, the total homocysteine concentrations were much lower in both extra-embryonic coelomic fluid and amniotic fluid than in maternal serum. All differences were significant (P < or = 0.01). CONCLUSIONS The comparatively high concentrations of methionine in extra-embryonic coelomic fluid and amniotic fluid, and the concomitant low levels of total homocysteine in these fluids, suggest a role for methionine metabolism during early human pregnancy.