Amniocentesis
Amniocentesis is a diagnostic test performed during pregnancy to assess the health of the fetus. It involves extracting and analyzing a sample of the amniotic fluid surrounding the fetus through an abdominal puncture.
General Description
Amniocentesis, also known as amniotic puncture, is a prenatal test that involves extracting a sample of amniotic fluid for further analysis. Amniotic fluid is a liquid that not only surrounds and protects the fetus during pregnancy but also contains fetal cells and chemicals produced by the fetus, making it a highly valuable source of information about the baby’s health.
When is it indicated?
Amniocentesis is performed between the 15th and 20th weeks of pregnancy. Generally, it is recommended for all pregnant women over the age of 35, as the risks of fetal abnormalities increase with maternal age. It is also indicated in cases of a history of spontaneous abortions, a family history of genetic disorders, positive results from a prior prenatal screening test, or detected abnormalities in an ultrasound.
Amniocentesis can detect various fetal conditions, primarily:
- Chromosomal abnormalities, such as Down syndrome, Turner syndrome, or Patau syndrome.
- Genetic disorders, such as cystic fibrosis or sickle cell anemia.
- Fetal malformations, such as spina bifida, anencephaly, and other neural tube defects.
- Fetal infections.
Additionally, amniocentesis is performed for the following purposes:
- To assess lung maturity when there is a risk of preterm birth. In this case, amniocentesis is performed between the 32nd and 36th weeks of gestation.
To drain an excess of amniotic fluid.
How is it performed?
In an amniocentesis procedure, a thin, hollow needle is used to puncture through the abdomen into the uterus. Using the syringe attached to the needle, between 20 and 25 milliliters of amniotic fluid are collected. Before the puncture, an ultrasound is performed to locate the position of the uterus and placenta and to select the optimal site for fluid collection. The puncture is guided by ultrasound.
Risks
Amniocentesis is an invasive procedure and, as such, may involve some risks, although they are very rare:
- Miscarriage: The risk is less than 1%, although it increases if amniocentesis is performed before the 15th week of gestation.
- Loss of amniotic fluid.
- Placental bleeding.
- Accidental puncture of the fetus or umbilical cord.
- Uterine infection.
- Transmission of a maternal infection to the fetus.
- Rh sensitization: The procedure may cause fetal blood cells to enter the maternal bloodstream. If the mother has Rh-negative blood and the fetus has Rh-positive blood, the maternal anti-Rh antibodies may destroy the fetal red blood cells, leading to a severe condition known as perinatal hemolytic disease.
What to expect from an amniocentesis
The patient lies on their back on the examination table with their abdomen exposed. To perform the ultrasound, the specialist applies gel to the patient’s abdomen and moves the ultrasound device (transducer) over the area.
After wiping off the gel, and using the ultrasound as a guide, the needle is inserted into the abdomen to extract the fluid. During the puncture and extraction, the patient must remain still. Although it is normal to feel a burning sensation or cramping during the procedure, amniocentesis is not particularly painful and does not require anesthesia. After removing the needle, the fetal heart rate is checked via ultrasound.
The procedure takes approximately 15 minutes. It is an outpatient process that does not require a recovery period, so the patient can return to their normal routine immediately, although it is recommended to rest for 48 hours. Additionally, mild cramping or slight vaginal bleeding, as well as a small leakage of amniotic fluid, may occur after amniocentesis.
If the pregnant person is Rh-negative and has not been immunized against Rh-positive blood, an injection of Rh immunoglobulin (commonly known as the Rh shot) is administered within 72 hours after the procedure. If prior testing confirms that the fetus is also Rh-negative, the shot is not necessary.
Specialties that request amniocentesis
Amniocentesis is requested and performed in gynecology and obstetrics clinics.
How to prepare
Amniocentesis does not require specific preparation. If performed in the early stages of pregnancy, the patient may need to have a full bladder, as this helps position the uterus more favorably for the procedure. In later stages, the bladder should be empty. Additionally, the patient must sign an informed consent form.
