Читать книгу Protocols for High-Risk Pregnancies - Группа авторов - Страница 53

Maternal serum levels of AFP (MSAFP) and unconjugated estriol (uE3) are both approximately 25% lower, and levels of hCG and inhibin‐A approximately twice as high in pregnancies complicated by trisomy 21. MSAFP, uE3, and hCG all tend to be decreased in pregnancies complicated by trisomy 18. The combination of AFP, uE3, hCG and inhibin‐A, commonly known as the quad screen, can detect about 80% of cases of trisomy 21, at a 5% false‐positive rate. Quad marker screening has the additional advantage of also screening for neural tube defects given the inclusion of MSAFP. Performance of serum screening tests is optimized by accurate ascertainment of gestational age, and, wherever possible, sonographic dating should be used instead of menstrual dating.