Consistency of the estimation of the 'odds ratio' for Down's syndrome with increasing gestational age

Abstract

SummaryThe aim of this study was to investigate the consistency of the estimation of the risk of a Down's syndrome birth in the face of changing human chorionic gonadotrophin (hCG) and a-fetoprotein concentrations. Starting at 15 weeks gestational age, blood samples were taken over a 4-week period, from six apparently normal volunteers. Serum α-fetoprotein and hCG were used to estimate the combined risk using a commercially available computer algorithm. During the period of the study the α-fetoprotein concentration almost doubled and the hCG concentration approximately halved. Despite a statistically significant relationship between odds ratio and gestational age the estimate of risk of Down's syndrome remained relatively constant.