Can Variable Plasma Volume Alterations Affect the Efficiency of the First Trimester Screening Test?

The aim of this study was to assess the effect of plasma volume alteration determined by hematocrit on biochemical parameters of the first trimester screening test.

Enrolled in this study were 1,424 pregnant women in their first trimester who underwent a first trimester screening test. Fetal Nuchal Trancluciency measurement was obtained by ultrasonographic evaluation. Blood samples were taken for complete blood count, serum free β-HCG, and PAPP-A between 11 and 14 weeks of gestation. The effect of plasma volume alteration on the screening test was evaluated. Mean corpuscular volume was used to rule out possible iron deficiency anemia.

There were 59 women with combined risk > 1/270. Of these 59 women, there were 21 false positive results (1.5%). Serum Htc significantly predicted the false positive cases (AUC: 0.839, p < 0.001). The optimal cutoff value was obtained at a value of 30.2% with 85% sensitivity and 75% specificity.

Our study suggests that the degree of plasma alterations may affect the serum levels of the biochemical components of the first trimester screening test for aneuploidy, thereby leading to false positive test results.