Amniocentesis is a prenatal diagnostic tool developed to detect common genetic defects in a child that could lead to health disorders. It can also be used to screen for any contagious diseases or infection in the foetus, or for discerning the gender of the foetus. Generally, the gender is ascertained via the help of ultrasound readings, but in cases that the ultrasound is not clear, or if the foetus has not developed much, this test can be performed.
This test is recommended when either or both parents have a family history of a certain health disorder or in cases of in vitro fertilization (IVF), recurrent miscarriages, or trauma to the body during pregnancy. In the event that the results of this test are inconclusive, another prenatal technique may be prescribed, depending on the stability of the mother and foetus. This technique is called the chorionic villus sampling, and involves scraping a minute amount of the chorionic villi that are responsible for attaching the placenta to the uterine wall. If this procedure is deemed to be too risky, then another option can be the sampling of blood in the umbilical cord.
In order to understand how and why amniocentesis is performed, one must first understand what amniotic fluid is, and why it needs to be tested.
What is Amniotic Fluid?
It is the protective liquid present in the amniotic sac which holds the foetus in the womb. It is a nourishing liquid for the developing foetus, and is rich in proteins, carbohydrates, lipids, and phospholipids. It is a clear and slightly yellowish liquid in which the foetus floats during the gestational period. It is produced as soon as the fertilized egg implants itself on the uterine wall. The maximum amount of this fluid that can be present is approximately 800 ml (at 34 weeks of pregnancy). The fluid is not stagnant, and is perpetually in motion due to foetal movements, movement of the mother, and also due to the foetus swallowing, inhaling, and releasing the liquid. It helps in the proper development of the foetus to regulate its body temperature, and also to cushion it from any sudden movements or physical stress that the mother may experience. Too little and too much of this liquid is dangerous. If it is present in lower amounts, the development of the foetus is hampered, whereas, if it is present in increased amounts, it indicates congenital birth defects in the foetus.
When and why should you get tested?
It is usually carried out when the woman is 14 - 16 weeks pregnant. It can be performed later, but not sooner. This test is usually scheduled only after consulting an obstetrician. Prior to the procedure, an ultrasound may be performed to confirm the stage of pregnancy. It is prescribed for the following reasons:
How is it tested?
- Family history or previous child with a genetic, chromosomal, or metabolic disorder
- Risk of neural tube defects
- Abnormal maternal protein levels, especially maternal serum alpha fetoprotein
- Possibility of sex-linked disorders
- Potential for premature birth
- Uterine infection during pregnancy
- Rh incompatibility
- Physical trauma or injury
- Recurrent miscarriages
- Maternal age more than 35 years
- Labour-like symptoms
- Idiopathic bleeding
It is carried out after administering a local anaesthetic
in the belly region. The procedure is conducted while constantly monitoring the mother's and the foetus' heart rate, and visualization of the position of the foetus is achieved by the help of a sonography. After the sterilization of the skin surface, the ultrasound helps guide the long, thin, and hollow needle through the abdomen to the amniotic sac in the uterus. It is carefully inserted so as to not puncture the foetus or any other part of the placenta
. Gently, a small amount (around 3 - 5 ml) of the amniotic fluid is aspirated out from the needle with the help of a syringe. Care has to be taken not to introduce any air into the sac, as it would lead to a foetal embolism. The collected fluid is placed in a light-protected bottle and sent for genetic and chromosomal analysis
. The needle is then gently and slowly removed, with the help of the ultrasound, and the punctured site is bandaged or sealed. After the procedure, it is recommended that the woman rest and not undertake any physically strenuous activities for at least 24 hours. Any signs of pain, bleeding, or disorientation must be reported to the doctor immediately.
What are the risks associated with it?
The associated risks include infection, foetal injury
, cramping, preterm labour, miscarriage, leaking of amniotic fluid, vaginal bleeding, dizziness, foetal embolism, etc. However, the occurrence of these conditions is quite uncommon, and the incidence of amniocentesis-related miscarriages is less than 1%.
What conditions can it detect?
It can be used to screen for and detect a wide variety of disorders and structural defects, such as:
- Down syndrome
- Edwards syndrome
- Turner syndrome
- Metabolic disorders
- Spina bifida
- Sickle cell anaemia
- Rh incompatibility
- Lung maturity (indicative of foetal respiratory disorders)
- Trisomy 13
- Trisomy 18
- Fragile X syndrome
Be it amniocentesis or a leaking amniotic fluid test
, the access to the liquor amnii (amniotic fluid) that surrounds the foetus in the womb has given us an opportunity to detect birth defects, and make pregnancies safer.