Feasibility of Using Plasma Rather Than Serum in First and Second Trimester Multiple Marker Down's Syndrome Screening

Objective To compare maternal plasma with serum for measuring markers currently used in first and second trimester screening for Down's syndrome. Setting A laboratory-based investigation of two sample types in assays used in prenatal screening for Down's syndrome. Methods A paired data-set included both plasma and serum from 101 pregnant women. A nested case/control data-set included only plasma samples from 34 first and 23 second trimester Down's syndrome pregnancies, each matched with six euploid controls. Analyte levels were measured and converted to multiples of the median (MoM). Results In the paired data-set, each of the five analytes (alphafetoprotein, unconjugated estriol, human chorionic gonadotropin, inhibin-A and pregnancy-associated plasma protein A) in serum and plasma was highly correlated (r > 0.970) and after conversion to MoM, the resulting distributions were equivalent (P > 0.7). In the matched data-set, plasma-based median MoM levels in cases were consistent with the published serum counterparts for all markers. Conclusions This study provides strong evidence that current serum-based prenatal screening can be performed equally well using plasma samples. This may prove useful, especially if secondary screening using a DNA-based test requires maternal plasma.