Prenatal Screening and Diagnosis Flashcards
High sensitivity
identifies a high percentage of affected individuals
High specificity
low number of false positives
First Trimester Screening
Maternal serum levels of PAPP-A and hCG + ultrasound
● ADJUSTS RISK for trisomy 18 and trisomy 21
● Trisomy 21 shows elevated hCG and decreased PAPP-A
● Trisomy 18 shows decreased hCG and decreased PAPP-A
● Results can be affected by maternal age, weight, race, and gestational diabetes
Quad Screen- Tri 18
Trisomy 18 will show decreased hCG, decreased inhibin A, decreased uE3, decreased AFP
Quad Screen- Tri 21
Trisomy 21 will show increased hCG, increased inhibin A, decreased uE3, decreased AFP
NTD Increased risk
when MoM (multiple of the median) for AFP is >2.0
Steroid sulfatase deficiency and SLO
should be considered with very low uE3 levels
Non-invasive prenatal testing/Cell-free placental DNA (NIPT)
● Can detect some trisomies (typically 13, 18, 21, may detect others)
● Can detect some microdeletions and microduplications
● Can detect sex chromosome aneuploidy (to an extent)
● May detect triploidy (SNP-based method only (Natera))
Findings in NTDs/ventral wall defects
o Spina bifida – Lemon sign (Chiari II malformation), banana sign (cerebellum)
o Anencephaly
o Gastroschisis
Other ultrasound findings
o Double bubble – duodenal atresia
o 2-vessel cord – may be a normal pregnancy, sometimes seen in trisomy 21
o Missing/absent limbs or digits - amniotic band syndrome
o Ventriculomegaly
o Congenital absence of the cavus septum pellucidum (CSP) – Septo-optic dysplasia
o Echogenic bowel – may be due to maternal cytomegalovirus (CMV) infection,
cystic fibrosis, Down syndrome, or bowel obstruction/stenosis
o Club foot
o Cleft lip (palate is usually not detectable on ultrasound)
o Structural heart defects
o Endocardial cushion defect – poorly formed septums of the heart – 60% have
trisomy 21
o Ebstein’s anomaly – improperly formed triscupid valve
Chorionic villus sampling (CVS)
● Diagnostic test
● Available between 11-13 weeks gestational age
● Samples placental tissue either transcervically or transabdominally
● Confined placental mosaicism may be present in 1-2% of cases
● Risk for miscarriage anywhere between 1/250 – 1/1000 depending on institution
Amniocentesis
● Diagnostic test
● Available at or after 16 weeks gestational age
● Samples amniotic fluid (baby pee ft. skin cells)
● Transabdominal
● Risk for miscarriage anywhere between 1/250 – 1/1000 depending on institution
Individuals considered high-risk
● Advanced maternal age
● Ultrasound findings suggestive of a trisomy
● History of a prior pregnancy/child with a trisomy
● Positive FTS or MMS
● One parent is a balanced Robertsonian translocation carrier
