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Genetic counseling:

Timing - variable, depending on the indication.

Mandatory prior to any invasive testing. Consultation is non-directive and includes risk assessment (including complete family and pregnancy history), education, and help in choosing prenatal tests appropriate for the patient. Studies show up to 50% higher detection for hereditary disorders when history is taken by genetic counselor rather than by an OB.

Nuchal Translucency:

Timing - optimally 11 to 12w6d, can be done up to 13w6d.

Performance and interpretation of the test requires certification by Fetal Medicine Foundation. Calculates a statistical risk for Down syndrome based upon maternal age, GA, history of previous child with DS, and NT. Useful for trisomy 13, 18 and Turner’s syndrome. Sensitivity ranges from 72-80% among certified centers, with a 5% positive test rate.

Combined Screen: (NT integrated with first trimester serum biochemistry.)

Timing – Serum PAPP-A and free beta hCG at 10w0d-13w6d (based upon CRL measurements), NT at 11w0d-13w6d. Sensitivity estimated at 95% for Down syndrome with a 2% positive test rate.

Performance issues: Lab work performed by Genecare - Second trimester maternal serum aFP is used to estimate risk of open neural tube defects is evaluated separately at 15-24 weeks.

Chorionic Villous Sampling (CVS):

Timing –10 to 14 weeks

Performance issues – 1% incidence of mosaisicm, or growth failure. 90% of procedures performed transabdominally.

Definitive test, useful for first trimester diagnosis of aneuploidy; does not test for neural tube defect so serum AFP is recommended at 17 weeks and targeted high-resolution ultrasound at 18 weeks. Excessive risk of miscarriage 1%; no increased risk of limb defects if performed after 10w0d.

Quad Screen:

Timing – serum test at 15 to 20 weeks

Maternal serum levels of AFP, hCG, UE3, and Inhibin A as well as maternal age, weight, and family history give a readjusted risk for Down syndrome, trisomy 18, and neural tube defects; sensitivity of 70% for Down syndrome with a 5% test positive rate.

Performance issues: Not useful for Down syndrome risk estimate with multiples, does not screen for trisomy 13, 47,XXX or 47,XXY.

Targeted High Resolution Ultrasound:

Timing – usually 16 to 18 weeks, or one week after the Quad or Integrated Screen test (IPRP2) is drawn.

Diagnostic test to assess any structural abnormalities or “soft signs” for Down syndrome including nuchal thickening, echogenic bowel, short limbs, pyelectasis, with a 50% sensitivity for detection of Down syndrome. Baseline age, quad or integrated screen adjusted risk can be adjusted up or down depending upon the findings .

Amniocentesis:

Timing – optimally 16 to 18 weeks though can be performed at 15 to 20 weeks

Detects 99.5% of all chromosome abnormalities; full karyotype results usually within two weeks. In cases of high risk from serum screening, frank anomalies by ultrasound, or advanced gestation we can also order Fluorescence In Situ Hybridization (FISH), which will detect aneuploidy of chromosomes 13, 18, 21, X, and Y with results in 24-48 hours. Assesses AFAFP levels to screen for neural tube defect and abdominal wall defects. Definitive invasive diagnostic test with up to 1% excessive risk of miscarriage.

Fetal Echocardiogram:

Timing – usually 20 – 22 wks

Diagnostic test to assess detailed cardiac anatomy in patients at high risk for cardiac anomalies e.g.: from IDDM, medication exposure, structural anomaly, or arrhythmia. Performed by Pediatric Cardiologist or Perinatologist. Sensitivity quite variable depending upon lesion and examiner.

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