Diagnosis may be suspected prenatally based on anomalies detected by fetal ultrasonography (eg, increased nuchal translucency, heart defect, duodenal atresia) or based on cell-free fetal DNA analysis of maternal blood or maternal multiple marker screening for levels of plasma protein A in late 1st trimester and levels of alpha-fetoprotein, beta - human chorionic gonadotropin (beta-hCG), unconjugated estriol, and inhibin in early 2nd trimester.