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stackedDNA.jpgDiagnostic Tests

Diagnostic tests are used to tell for sure if your baby has Down Syndrome, Trisomy 18 or an Open Neural Tube Defect (ONTD). Most times the results of your amniocentesis or Chorionic Villus Sampling will be normal. Remember, most babies are born healthy.

Amniocentesis

The test which can look specifically for a chromosomes abnormality in a pregnancy is called amniocentesis.  It is usually done at about 16 weeks of pregnancy, and involves the insertion of a needle through the woman’s abdomen and the removal of a small amount of fluid, which contains fetal cells, from the amniotic sac.  The amniocentesis has a risk for miscarriage of 1 in 400.  The final results take 4 weeks to return to your doctor, but an abnormal result is usually available much sooner than this.  Amniocentesis can also detect most neural tube defects (like Spina Bifida) by measuring the amount of a substance called AFP (alpha-fetoprotein) in the amniotic fluid.  The general population risk for Spina Bifida is 1 in 1000 and not influenced by maternal age.

Chorionic Villus Sampling (CVS)

  • CVS is a prenatal test used to diagnose or rule out certain birth defects. It studies DNA, chromosomes and enzymes of the fetus. A tiny tissue sample is taken from outside the sac where the fetus develops (chorionic villi).
  • The sample is obtained either by passing a small catheter through the vagina and cervix into the uterus, or by inserting a fine needle through the abdominal wall. The test is usually performed 10-12 weeks after a woman's last menstrual period.
  • It is not routinely offered to all pregnant women as the test carries a small risk for miscarriage and/or other complications (ie. infection, injury to baby, spotting/cramping).
  • CVS is slightly more likely than amniocentesis to give inconclusive results, thus requiring an amniocentesis be performed. It is a diagnostic test. It does not guarantee a normal pregnancy outcome.
  • CVS does not detect nerual tube defects. Patients should have a blood test to measure their alpha fetoprotein to rule out spinabifida.

Level II ultrasound

Level II ultrasounds are performed at 18-19 weeks of pregnancy.  This ultrasound takes a detailed look at the baby’s anatomy.  A Level II ultra sound can detect many birth defects, but not all abnormalities.  A Level II ultrasound is used to detect open neural tube defects such as Spina Bifida and anencephaly.

Nuchal Translucency

Nuchal translucency is the thickness of the skin at the back of the neck of the developing baby.  An ultrasound and blood tests are done in early pregnancy to provide an integrated risk of having a baby with Down Syndrome, trisomy 18 or an open neural tube defect. This service is not available in our area.