Genetic Amniocentesis

Genetic amniocentesis is a screening examination done during pregnancy to diagnose chromosomal abnormalities in the fetus. Usually an amniocentesis is done at between 16-20 weeks of pregnancy (gestation). During this procedure amniotic fluid is removed for testing. The amniotic fluid contains cells that the baby sheds naturally, from their skin, lungs and urinary tract. Cells and proteins within the amniotic fluid are examined in the lab to test for specific fetal disorders, such as chromosomal disorders like Down syndrome, Patau syndrome, and Turner syndrome. Alpha-fetoprotein (AFP) also found in the amniotic fluid and can be measured in the laboratory.

An amniocentesis takes approximately 45 minutes, the majority of which is during a detailed ultrasound. Ultrasound is also used during the procedure.

An amniocentesis is offered to
  • A woman who will be 35 years old or more at the time of delivery.
  • A couple with a child or other family member with a chromosomal abnormality.
  • A pregnant person who received an abnormal result from other screenings, such as the NIPT (non-invasive prenatal test), which is used to screen for chromosomal abnormalities in the fetus, such as Down syndrome. This is a blood test that can be done starting at 10 weeks of gestation.
  • A couple in which one partner has a chromosomal rearrangement (for example, a translocation or an inversion).
  • A couple with an increased risk of having a child with a genetic disease for which testing is available.
  • A couple with a child with a neural tube defect (for example, spina bifida or anencephaly).
    If you will be 35 years old or older when your baby is due and do not want an amniocentesis, speak to your doctor for alternative blood testing to screen for chromosomal abnormalities. Only certain abnormalities can be screened this way, such as those for Down syndrome. If blood tests reveal abnormalities, an amniocentesis is strongly recommended. If you still choose not to undergo the procedure, it is important you speak to your obstetrician about the possible implications and create a plan for the rest of your pregnancy and the postpartum.

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