Relationships between Cell-Free DNA and Serum Analytes in First and Second Trimesters of Pregnancy

To assess the relationship between first- and second-trimester cell-free DNA levels and maternal serum screening markers.First- and second-trimester residual maternal serum samples from 50 women were obtained. First-trimester (pregnancy-associated plasma protein A and beta-hCG) and second-trimester serum analytes (beta-hCG, alpha-fetoprotein, unconjugated estriol, and inhibin A) had been measured at the time of sample receipt. All fetuses were male as confirmed by birth records. Cell-free DNA was extracted and measured by real-time quantitative polymerase chain reaction amplification using glyceraldehyde phosphate dehydrogenase and DYS1 as markers of total DNA and fetal DNA, respectively. Determination of linear associations between first- and second-trimester serum markers and cell-free DNA levels using Pearson correlations was performed.Statistically significant correlations between first-trimester pregnancy-associated plasma protein A multiples of the median and both total (r=0.36, P=.016) and fetal (r=0.41, P=.006) DNA in the first trimester were observed. There were no significant correlations between first-trimester serum human chorionic gonadotropin or any second-trimester serum marker with DNA levels.Correlation between serum pregnancy-associated plasma protein A and first-trimester circulating cell-free fetal and total DNA levels is a novel finding. Pregnancy-associated plasma protein A is a glycoprotein of placental origin, and its correlation to cell-free fetal DNA in maternal serum suggests a common tissue origin through apoptosis of placental cells. However, because pregnancy-associated plasma protein A and cell-free DNA were only marginally correlated and cell-free DNA can be reliably detected in the first trimester, the addition of cell-free DNA to serum screening strategies may be helpful in predicting adverse pregnancy outcome.II.