Tools of Prenatal Diagnosis

Tools of Prenatal Diagnosis
By:Julie Moldenhauer, MD
Reproductive Genetics
Maternal Fetal Medicine
Obstetrics and Gynecology

Objectives:
* Discuss various prenatal screening and testing tools
* Discuss the timing of the various tools in gestation
* Discuss benefits and risks of various options
* Review the difference between screening and testing
Baseline Risk for Birth Defects in the General Population is 3-5%
What Can We Diagnose in the Prenatal Setting?
* Structural Abnormalities
o Congenital heart disease
o Spina bifida
o Gastroschisis
* Chromosomal Abnormalities
o Trisomy 21
o Triploidy
* Infections
o Parvovirus
o Cytomegalovirus
o Toxoplasmosis
* Growth Abnormalities
* Hematologic Abnormalities
o Anemia
o Thrombocytopenia
* Functional Defects
o Arthrogryposis
o Renal dysfunction
* Syndromes
o Skeletal Dysplasia
o Diabetic embryopathy

Prenatal Diagnosis Tools

* History
o Personal History
o Family History
* Population Screening
* Serum Screening
* Ultrasound
* Fetal MRI
* Invasive Diagnosis
o Chorionic villus sampling
o Amniocentesis

History is a Screening Tool!
o Maternal Age
+ > 35 years at delivery
o Obstetric History
+ Prior baby born with Down syndrome
+ Prior stillbirth
o Medical History
+ Is mom diabetic? How well controlled is her sugar?
+ Does she have PKU?
+ Is she hypertensive?
o Medication Exposures
+ What medications?
+ When was the exposure?
o Environmental Exposures
+ Does she work in a preschool and was exposed to parvovirus?
+ Is she exposed to high doses of radiation?
o Family History
+ Brother with hemophilia
+ Uncle with cystic fibrosis
+ Ethnic background
+ Consanguinity

As maternal age increases, the risk for aneuploidy increases. This is due to maternal meiotic nondisjunction.
Maternal age > 35 at the time of delivery is considered “Advanced Maternal Age” or AMA
The risk for recurrence of chromosome abnormalities is dependent upon the genetic mechanism involved.
Trisomy: 1% or maternal age-related risk
Translocation:
Maternal carrier: 10-15%
Paternal carrier: 2%

Down syndrome phenotype caused by trisomy 21
Down syndrome phenotype caused by 14;21 translocation

Maternal Diabetes: Reproductive Risks
* Fetal and Neonatal
o Congenital anomalies: 6-12%
o Intrauterine fetal demise
o Macrosomia – Shoulder dystocia
o Growth restriction
o Hyperbilirubinemia
o Hypoglycemia
o RDS
o Polycythemia
o Organomegaly
o Long term – obesity and carbohydrate intolerance
* Obstetric
o Spontaneous preterm labor
o Polyhydramnios
o Preeclampsia (15-20%)
o Intrauterine growth restriction
o Shoulder dystocia
o Cesarean delivery

Caudal Regression Syndrome
Teratogen Exposure
Fetal growth
Organogenesis complete
Eyes, heart, lower limbs
Axial skeleton, limb buds, musculature
CNS
None, “ALL or NONE”
* Examples:
* Accutane
* ACE inhibitors
* Lithium
* Antiepileptic drugs (AEDs)
* Anticoagulants: warfarin
* Antidepressants
* Methotrexate
* Thalidomide

Teratogen Exposure
* Fetal effects are timing and dose dependent

* Each medication is assigned a pregnancy category based on available data; A-D, X
* www.Reprotox.org
* www.otispregnancy.org

Ultrasound images of fetal hydrops – abnormal collection of fluid in multiple body compartments.
Mom works at a daycare where there was a Parvovirus B19 or Fifth Disease outbreak 4 weeks ago. Parvovirus causes fetal aplastic anemia that can be life-threatening.

Suspicion of diagnosis by altered maternal serum titers of Parvo IgG and IgM and confirmed by amniotic fluid PCR for Parvo.
Confirmed Parvo infection in a fetus with hydrops can be treated with intrauterine blood transfusions.

Fetal Ultrasound Showing Cardiac Rhabdomyoma
Fetal MRI Showing Tubers
Prenatal Findings Consistent with Tuberous Sclerosis Confirmed as Neonate
Screening for Genetic Disease
Ethnic Group Disease
African American Sickle Cell Disease: 1/12
Mediterranean Beta-Thalassemia: 1/30
Southeast Asian Alpha-Thalassemia: 1/20
Caucasian Cystic Fibrosis: 1/25

ASHKENAZI JEWISH ANCESTRY
GENETIC CARRIER TESTING
Gaucher’s disease
Bloom syndrome
Mucolipidosis IV
Niemann-Pick disease type A
Fanconi Anemia Group C
Familial Dysautonomia
Cystic Fibrosis
Canavan disease
Tay-Sachs disease
Detection rate
Carrier Frequency
Disease Incidence
Testing and screening options should be made available to all pregnant women
Prenatal Screening & Testing
When Screening
(risk estimate)
Definitive
(Invasive)
First Trimester
FIRST screen*
Ultrasound
CVS

Second Trimester
Maternal Serum Screen*
Ultrasound
Amnio
Cordo
*First and Second Trimester Integrated and Sequential Screening

Test Performance
* Detection rate – the percentage of affected that are test “positive”
o (the higher, the better)
* False positive rate – the percentage of unaffected that are test “positive”
o (the lower, the better)

Goals in Prenatal Screening:
* High sensitivity - low false positive rate
* Wide availability
* Reproducibility and accuracy
o Human error, testing conditions

First Trimester Screening
o 11-13 6/7 weeks (CRL 39-79 mm)
o Maternal serum sample for PAPP-A and Free b-HCG
o Ultrasound for Nuchal translucency
o Detection Rates:
+ 80% for Trisomy 21
+ 90% for Trisomy 18
+ Does not screen for NTDs

PAPP-A
b-HCG
T21
T18

Increased NT vs Cystic Hygroma
* Increased NT > 95th%
o With or without septations
* Structural defects
o Heart defects most common
* Syndromic associations
* Chromosomal defects
o Exponential increase with increased NT
o 50% Down syndrome
o 25% Trisomy 13 or 18
o 10% Turner Syndrome
o 5% Triploidy
o 10% other

NT > 3 mm is ABNORMAL
Second Trimester Serum Screening: Chromosome Abnormalities

* Maternal Serum Screening
o 15-20 weeks
o Triple screen: 60% for T21
o Quad screen: 70% for T21
o Gestational Age Dependent**
* Targeted Ultrasound
o 50% aneuploid fetuses will have ultrasound markers
AGE +AFP +hCG +uE3 +InhA
DR at 5% FPR
2nd trimester
single double triple quadruple
Serum Screening Test Performance at a fixed 5% False Positive Rate (Dating by Ultrasound)

Prediction
SURUSS
FASTER
Second Trimester Serum Screening: Neural Tube Defects
* Neural Tube Defects
o Spina Bifida
o Anencephaly
* AFP increased in “open” defects
* Sensitivity
o 90% anencephaly
o 80-85% open spina bifida
* False positive – 3-4%
Interpreting a Quadruple Screen

Bottom Line: AFP is increased with NTDs and decreased with chromosome abnormalities

Elevated MSAFP
* Incorrect Dates – most common reason
* Multiples
* Congenital Nephrosis
* Ventral Wall Defects
* IUFD
* Adverse Pregnancy Outcomes
o Stillbirth
o Placental abruption
o Preterm labor
o Oligohydramnios
o IUGR

Ultrasound detection of aneuploidy
Nuchal Fold
CPC
Duodenal atresia
Pyelectasis
Clinodactyly
Second trimester sonographic markers of Down syndrome
AV Canal
Trisomy 18
Edward Syndrome
* Close to 90% detected by prenatal scan
* US:
o Growth restriction
o Clenched fists
o >90% with cardiac defects
o Multiple malformations
* Grim prognosis
o 50% Stillbirth
o 50% die within the first week
o 5-10% survive the first year

Trisomy 13
Patau Syndrome
Fetal Anatomy by Ultrasound
Ventral Wall Defect
Gastroschisis
NTDs
Lemon Sign
Banana Sign
Meningomyelocele Sac
Meningomyelocele Sac on Newborn
PGD: Preimplantation Genetic Diagosis
Pearls for Invasive Testing
* Risk for Sensitization
o Mom Rh negative – Rhogam
o Other antibodies may increase risk
* Risk for Infection transmission
o Hepatitis B
o Hepatitis C
o HIV
o Need to know familial mutations prior to performing invasive testing

Chorionic Villus Sampling
* Performed 10-14 weeks
* Does not test for ONTD
* Technique – “Placental biopsy”
o Transabdominal
o Transcervical
* Risk for limb reduction defects if performed < 9 weeks
* Loss rate 1/100-1/200
* Risk for mosaicism (~1%)

Transcervical
CVS
Transabdominal
Performed at 10-14 weeks
Amniocentesis
* > 15 weeks
* Loss rate 1/200 (probably closer to 1/300-1/500)
* Tests for ONTD
* Technique
o Fine gauge needle
o Ultrasound guidance
o Aspiration of 20-30 cc of fluid

PERFORMED ROUTINELY 15-20 WEEKS
Ultrasound Guided Procedure
AMNIOCENTESIS
Cordocentesis
* Percutaneous Umbilical Blood Sampling
* Loss rate 1/100-1/200
* Typically done after 18 weeks
* Ability for:
o Rapid karyotype
o Blood/platelet counts
o Direct fetal injections/transfusions

Fetal Blood Sampling
“PUBS”
Conclusions

* Many options for screening and testing.
* Prenatal screening should provide the most effective test to the greatest number of women.
* The best method of screening is yet to be determined.
* Patient preference should be considered.
* Testing and screening should be available to all women.

Tools of Prenatal Diagnosis.ppt