What is amniocentesis?
Amniocentesis is an invasive diagnostic procedure that involves the examination of cells in the amniotic fluid from around the baby. If indicated, it is generally done between 15 -19 weeks of pregnancy. The cells in the amniotic fluid originate from the baby and so the chromosomes present in these cells are the same as those of the baby.
Why is an amniocentesis offered?
- Positive screening test including nuchal translucency risk assessment and/or NIPT
- Maternal age: some women older than 35 year declined screening tests in lieu of a definitive test
- Previous history of an affected child, parental chromosomal abnormalities or rare genetic diseases
How is amniocentesis performed?
You will have the procedure explained to you by our specialist doctor and sign a consent form. Amniocentesis involves passing a thin needle into the uterus in order to aspirate a small amount of amniotic fluid. The needle is carefully observed using ultrasound to ensure correct placement.
The amount of fluid removed by amniocentesis will reaccumulate within a few hours.
The procedure lasts about 5 minutes and afterwards we check that the fetal heart beat is normal.
What should I expect after amniocentesis?
For the first couple of days you may experience some abdominal discomfort or crampy period-like pain. You may find it helpful to take simple analgesia such as paracetamol.If there is a lot of pain, bleeding, loss of fluid from your vagina or if you develop a temperature please seek medical advice.
When can I expect to get the results?
Chromosomes contain our DNA that give instructions to our cells on how to form, develop and functions. Changes in our chromosomes and DNA can therefore lead to developmental defects and also affect function. There are a number of tests that will be considered:
- Fast FISH: Special dying technique to give answer within 24-48 hours on the most common chromosome abnormalities involving chromosomes 21, 18, 13 X & Y. It provides a rapid answer on the risk of Down syndrome
- Karyotype: Cells are cultured in a medium then fixed and stained. This test will count all chromosomes and report on some structures changes called deletion(missing DNA) and duplications(extra DNA) as well as translocations (exchange of DNA). This result takes 2-3 weeks to become available.
- Chromosome micro-array testing(CMA): This is the latest laboratory technology that allow us detailed information about missing or extra DNA. This result takes 2-3 weeks to become available.
A patient will receive a personal phone call to discuss results and options and we will facilitate additional opinions if required.
What are the risks associated with amniocentesis?
The risk of miscarriage due to amniocentesis is about 0.5% and this is the same as the risk from chorion villus sampling. If you were to miscarry due to the test, this would usually happen within the next five days.