Second trimester amniotic fluid oestriol, dehydroepiandrosterone sulphate, and human chorionic gonadotrophin levels in Down's syndrome.
OBJECTIVE: To investigate the reason for low maternal serum unconjugated oestriol (uE3) and raised human chorionic gonadotrophin (hCG) levels in Down's syndrome pregnancies. DESIGN: Measurement of uE3, total oestriol (tE3), dehydroepiandrosterone sulphate (DHEAS), a precursor of oestriol, and hCG in 15-20 week amniotic fluid samples from pregnancies with and without Down's syndrome. SETTING: The retrieval and use of stored amniotic fluid samples collected from women who had had an amniocentesis for antenatal diagnosis. SUBJECTS: 45 women with a Down's syndrome pregnancy and 224 unaffected controls of the same gestational age. RESULTS: The median level of amniotic fluid in affected pregnancies was low for uE3, tE3 and DHEAS but high for hCG: 0.50, 0.46, 0.35 and 1.58 multiples of the normal median, respectively. CONCLUSION: These results suggest that the abnormal maternal serum levels of uE3 and hCG in affected pregnancies are due mainly to abnormal feto-placental synthesis, rather than feto-maternal transfer.