An initial study of trisomy 21 cases showed that prior to 10 weeks, maternal serum levels of intact hCG in the early first trimester are lower than normal. Here we further study the levels prior to and after 10 weeks of gestation to further establish whether or not the intact hCG is effective as a very early screening marker.Methods
Fifty-nine samples from pregnancies with trisomy 21 were identified, 31 were collected between the sixth and ninth weeks of gestation and 28 after the tenth week. A series of 629 gestational age-matched samples collected during the same period formed the control group. Intact hCG was measured by a DELFIA assay.Results
The multiples of the median (MoM) in cases (n = 31) collected prior to 10 weeks were 0.79 (CI 0.62-0.98) at a median gestation of 9.1 weeks. Prior to 9 weeks (n = 14) the median was 0.774 (CI 0.54-1.09) at a median gestation of 8.5 weeks. Modelling the detection rate for a 3 or 5% false-positive rate when screening using intact hCG, free β-hCG and PAPP-A at 8-10 weeks of gestation indicated that 71 or 77% of cases would be detected.Conclusion
More data are needed to establish a secure MoM for intact hCG in pregnancies prior to 10 weeks, before it could be considered a suitable screening marker.