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PRENATAL DIAGNOSIS

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Indications
  1. Maternal age > 35 (increased risk of some chromosomal anomalies)
  2. abnormal MSS or ultrasound
  3. past history of pregnancy with chromosomal anomaly or genetic disease
  4. either parent a known carrier of a genetic disorder or balanced translocation
  5. three or more miscarriages
  6. family history of chromosomal anomaly, genetic disorder, birth defect,
    or undiagnosed mental retardation
  7. consanguinity
Amniocentesis

  • ultrasound-guided transabdominal extraction of amniotic fluid at
  • 15-16 weeks gestation to identify genetic problems such as trisomies
  • during 3rd trimester for assessment of fetal lung maturity
L/S ratio: if > 2:1, fetal lungs are mature enough that RDS less likely to occur
  • used to quantitate amniotic fluid bilirubin concentration in Rh-isoimmunized pregnancies advantages

    1. screen for NTD (acetyl cholinesterase and amniotic AFP)
    2. more accurate genetic testing 
  • disadvantages

    1. 0.5% risk of spontaneous abortion
    2. results take 10-14 days,FISH (Fluorescent In Situ Hybridisation)available in 72 hours
  • in women over 35 years, the risk of chromosomal anomaly (1/180) is greater than the increased risk of miscarriage from the procedure, so it
    is offered routinely

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Chorionic Villus Sampling (CVS)

  • needle through abdomen or catheter through cervix at 10-12 weeks
  • advantages

    1. enables pregnancy to be terminated earlier
    2. more rapid karyotyping, DNA tests, chromosome status, biochemical assay (results in 48 hours; do not have to wait for culture)
    3. increasing availability of probes to allow diagnosis of genetic abnormalities (i.e. FISH)

  • disadvantages

    1. 1-2% risk of spontaneous abortion
    2. does not screen for neural tube defects (NTD)
    3. risk of limb injury
    4. poor test because of genetic mosaicism

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PRENATAL DIAGNOSIS PRENATAL DIAGNOSIS Reviewed by Radiology Madeeasy on December 27, 2010 Rating: 5
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