Amniocentesis is a medical procedure primarily used in prenatal diagnosis of chromosomal abnormalities and foetal infections. It can also be used to determine gender of the foetus or paternity of potential fathers. This procedure extracts a small sample of the amniotic fluid which contains foetal DNA. These DNA samples are used to determine if there is a chromosome abnormality or infection. There is also a condition called polyhydramnios where the amniotic sac accumulates too much amniotic fluid and this procedure can drain some of the excess. A genetic amniocentesis is generally performed between 15 and 20 weeks.
What are the risks?
- Leaking amniotic fluid: sometimes amniotic fluid can leak through the vagina following an amniocentesis. In most cases the amount of fluid lost is minimal and generally stops within a week.
- Risk of miscarriage: when performed in the second trimester, studies show that there is up to a 0.6% chance of miscarriage. This statistic dramatically increases if the amniocentesis is performed before 15 weeks.
- Needle injury: the baby may move a body part into the path of the needle.
- Rh sensitivity: if the mother has Rh negative blood, she will be given an injection of Rh immune globulin which prevents the mother from making antibodies that will attack a Rh-positive baby
- Infection: by introducing anything into a sterile environment (uterus and amniotic sac) you run the risk of introducing foreign bacteria that can cause an infection
- Infection transmission: if the mother is positive for HIV/AIDS, hepatitis or toxoplasmosis, an amniocentesis risks the infection being transmitted to the baby
Preterm labour: amniocentesis procedures pierce through the uterus which can irritate the uterus and cause preterm labour
Amniotic fluid embolism: An amniotic fluid embolism (AFE) is a birth emergency and is believed to happen to 1 in 20,000 births. An AFE is when amniotic fluid enters the mothers blood stream and causes cardio-respiratory (heart and lungs) collapse and bleeding.
What you can expect
Prior to insertion of the needle, an ultrasound will be conducted to determine the location of the placenta, foetal position and movements, and characteristics of the amniotic fluid. All gel and ultrasound equipment uses sterile gel and then the abdomen is cleaned with antiseptic to lower the risk of infection. There is no anaesthetic used in this procedure. Expect to feel a sting as the needle enters the skin and possible cramps as the needles passes through the uterus. The tools used to complete this procedure are coated in heparin to prevent clotting.
The needle is inserted through the mother's abdominal wall, through the uterus and then pierces the amniotic sac while being guided by ultrasound. The physician punctures the sac in an area away from the foetus and extracts about 20ml of fluid. The first 2ml is often discarded due to being mixed with maternal blood cells. This step can be done with a single or double needle depending on the individual patients contributing factors or the physician's preference.
Foetal cells are separated and extracted from the fluid. The cells are grown, fixed and stained before being examined under a microscope for abnormalities. The most common being down syndrome (trisomy 21), edward's syndrome (trisomy 18) and turner syndrome (monosomy X). These samples are also tested for foetal infection and intra-amniotic inflammation.
After the procedure, your health care provider will continue to monitor baby's heartbeat for a period. For the initial 24 hours following the procedure the mother will be instructed to stay on house rest allowing for non-strenuous daily activities like personal hygiene. A follow up ultrasound will be scheduled about one week after the procedure. They will ensure foetal viability and assess the healing of the puncture site. Some results can take up to 4 weeks.
Contact a health provider immediately if:
- vaginal bleeding
- loss of amniotic fluid through the vagina
- severe uterine cramping lasting more than a few hours
- redness and/or inflammation where the needle was inserted
- unusual foetal activity or lack of foetal movement
Genetic amniocentesis is a reliable way of ruling out or confirming a diagnosis of some genetic abnormalities. However, amniocentesis cannot identify all genetic conditions and birth defects. In the event of a positive result for any chromosome abnormalities or birth defects your health care providers will link you in with counselling services. These services will help your family work out a way to manage the condition if you choose to continue the pregnancy. You will also be given the choice to have a late stage termination of the pregnancy.
There is no right or wrong choice to make. Every mother and/or family deserves to have support with any decision made, as both come with their own obstacles.