Inclusion of serum marker measurements from a previous pregnancy improves Down syndrome screening performance.
A predisposition for high or low levels of serum marker concentrations in second trimester Down syndrome screening reflecting itself in consecutive pregnancies in the same woman has been demonstrated, but hitherto the possible effect of including previous marker results in a current risk evaluation has been considered negligible. Using published data on correlations between the markers AFP, hCG and uE3 in different normal pregnancies in the same women and age-related a priori probabilities we found, that in triple marker screening the inclusion of results from a previous pregnancy in a likelihood ratio based risk calculation could increase the detection rate for women having had an earlier pregnancy from 68.0 per cent to 70.2 per cent at a risk cut-off = 1:250. The screen positive rate for normals for the same population of women, being on average older than the total population, fell from 7.1 per cent to 6.8 per cent. These figures, that are based on an assumption of the same correlations between one normal and one Down syndrome pregnancy as between two normal pregnancies, corresponds to an expected reduction, in the population considered, of the number of children born with Down syndrome of 6.7 per cent and of the number of screen positive normals of 4.7 per cent. Considering that this can be achieved at no extra cost, it is concluded that implementation of a procedure for taking information from previous pregnancies into account in second trimester screening should be considered at centres that can handle the software problems involved in doing so. However, better data on the correlations between a normal and a subsequent Down syndrome pregnancy in the same woman should probably be awaited before this is done.
Larsen
S O
SO
Biostatistical Department, Statens Serum Institut, Copenhagen, Denmark. sol@ssi.dk
Christiansen
M
M
Nørgaard-Pedersen
B
B
D015415:Biomarkers / Q000097:blood*; D006063:Chorionic Gonadotropin / Q000097:blood; D004314:Down Syndrome / Q000097:blood* / Q000175:diagnosis*; D004964:Estriol / Q000097:blood; D005260:Female; D006801:Humans; D011247:Pregnancy; D011296:Prenatal Diagnosis; D012307:Risk Factors; D000509:alpha-Fetoproteins / Q000032:analysis
D015415:Biomarkers; D006063:Chorionic Gonadotropin; D000509:alpha-Fetoproteins; D004964:Estriol