Exam 3 - Trisomy Assessment

Genetic Screening Options

Biochemical/serum marks from mother

Sonogram of fetus

Diagnostic Genetic Testing Options

Chorionic villus sampling (CVS)

Amniocentesis

Cell-free fetal DNA (cfDNA) in maternal blood

Human Chorionic Gonadotropin (hCG)

Produced by fetal trophoblasts

Normally elevates in 1st trimester, declines & plateaus by 20 weeks

Reasons for increased hCG levels

Incorrect dates - fetus older than expected

Multiple babies

Trophoblastic/placental disease

Trisomy 21

Reasons for decreased hCG levels

Incorrect dates - fetus younger than expected

Fetal demise

Ectopic pregnancy

Trisomy 18

Alpha-Fetoprotein (AFP)

Produced within fetal neural and GI tracts

Enters amniotic fluid via fetal urination, then to maternal circulation through placenta

Reasons for increased AFP levels

Incorrect dates - fetus older than expected

Multiple babies

Placental disease

Leakage from fetus into amniotic fluid via abdominal wall or neural tube defects

Reasons for decreased AFP levels

Incorrect dates - fetus younger than expected

Fetal death

Trisomy 21 or 18

Blockage in fetal urogenital tract

Molar pregnancy

1st Trimester Screening

10-14 weeks

Screens for Trisomy 21

88% accuracy

2nd Trimester Screening - Penta Screen

15-20 weeks

Screens for birth defects & aneuploidy risk

83% sensitivity

Values that indicate Trisomy 21

Increased hCG

Increased maternal age

Increased nuchal translucency

Decreased AFP

Decreased PAPP-A

Values that indicate Trisomy 18

Decreased hCG

Decreased AFP

A nuchal translucency error of ______ can simnifically alter risk estimates

0.4 mm

Non-Leathal Aneuploidies

Trisomy 21

Turner's syndrome

Lethal Aneuploidies

Trisomy 18

Trisomy 13

Triploidy

Trisomy 21

Down syndrome

Extra 21st chromosome

Most common aneuploidy

Low IQ always present

Trisomy 21 Major Markers

Absent nasal bone

Duodenal atresia

Cardiac defects

Cystic hygroma

Omphalocele

Echogenic bowel

Trisomy 21 Minor Markers

Sandal gap

Clinodactyly

Short long bones

Pyelectasis

Turner's Syndrome

Absent X chromosome or 46X0/46XXX

Only in females

Mimics Noonan's syndrome (males)

Features of Turner's Syndrome in a Fetus

Horseshoe kidneys

Aortic coarctation

Features of Turner's Syndrome in a Child/Person

Webbed neck

Shield chest

ABNL elbow angle

Trisomy 18

Edward's syndrome

Extra 18th chromosome

Features of Trisomy 18

Strawberry-shaped head

Chorioid plexus cysts

Septal defects

Clenched fists/talipes/rocker bottom feet

Facial defects

Trisomy 13

Patau syndrome

Extra 13th chromosome

Features of Trisomy 13

Holoprosencephaly

Cleft lip & cyclopia

Polydactyly

2 vessel cord

Cystic hygroma

Triploidy

Extra chromosome on all sets - 69 total

Features of Triploidy

Hydrancephaly

Syndactyly

FGR

Partial molar pregnancy