Maternal Serum Invasive Trophoblast Antigen and First-Trimester Down Syndrome Screening

screening is still performed mainly in the second trimes-ter, using 3 or 4 markers. Moving screening into the first trimester has the advantage of earlier diagnosis. Cur-rently, first-trimester screening typically includes ma-ternal serum pregnancy-associated plasma protein-A (PAPP-A), the free -subunit of human chorionic gonad-otropin (free ), and ultrasound measurement of nuchal translucency thickness (NT). The current report de-scribes a case–control study of serum invasive tropho-blast antigen (ITA) and its possible inclusion in first-trimester screening for Down syndrome. Methods: As part of an earlier observational study, serum samples from 54 Down syndrome and 276 matched unaffected pregnancies were collected between 9 and 15 weeks of gestation. Samples had been ali