Fetal Evaluation and Prenatal Dignosis

• α-Fetoprotein (AFP)


  Elevated with fetal neural tube defects, multiple gestation pregnancies, underestimated gestation age, ventral abdominal wall defects, fetal demise, or fetal edema or skin defects. Low AFP levels are associated with overestimated gestation age, trisomies 18 and 21, and intrauterine growth retardation.
• Triple/quadruple markers


  Used in conjunction with ultrasound findings as a noninvasive method to assess the fetus for the possibility of trisomy syndromes. The three classic second-trimester screening markers are AFP, unconjugated estriol (uE3), and the β-subunit of human chorionic gonadotropin (β-HCG). More recently, the use of inhibin-A has been introduced to increase the detection rate of Down syndrome.
• Trisomy 21


  Suggested by findings of low AFP and uE3 and high β-HCG and inhibin-A.
• Trisomy 18


  Suggested by low levels of AFP, uE3, and β-HCG.
• Ultrasound


  • Used to assess gestation age and fetal growth and to evaluate for major fetal anomalies. The finding of increased nuchal translucency may indicate the presence of trisomies 13, 18, and 21 and Turner syndrome, as well as structural anomalies such as congenital heart disease.
• Chorionic villus sampling (CVS)


  The use of villus tissue from the chorion of the trophoblast that is collected at 10–13 weeks' gestation. Karyotype, gene sequencing, and enzyme analyses from CVS can be used to assess for genetic and metabolic disorders.
• Amniocentesis


  The use of amniotic fluid containing sloughed fetal cells collected at 16–18 weeks' gestation. This technique can be used to assess for the same genetic diseases as CVS.
• Percutaneous umbilical blood sampling

  Involves obtaining a sample of fetal blood to assess for hematologic abnormalities, genetic disorders, infections, and fetal acidosis. It can also be used to administer medications or blood transfusions to the fetus.
• Noninvasive prenatal testing (NIPT)


  Involves the isolation of fetal cells extracted from a cell-free DNA sample of maternal blood. It is used for assessment of fetal trisomies 13, 18, and 21, and has the potential to replace more invasive forms of sampling for all genetic tests in the future.