Amniocentesis

What is amniocentesis?

Amniocentesis is a test done to check the health of the unborn baby. The baby grows in the uterus, in a special bag of water called the amniotic sac. In amniocentesis, the doctor uses a needle to remove a small amount of fluid from the amniotic sac. The amniotic fluid sample is analysed in the lab. Amniotic fluid contains cells from the baby that can be screened for certain genetic problems like Down’s syndrome. Amniocentesis may also be done near the end of a pregnancy to test the maturity of a baby's lungs.

When is it done?

It is usually done between the 15th and 18th weeks of pregnancy, for genetic screening. The doctor may advise amniocentesis in the following cases:

• Mother’s age more than 35 years.
  
• Prenatal tests show an increased likelihood of a problem with the baby.
  
• Family history or a previous delivery of a child with genetic problems.
  
• History of frequent miscarriages.

Amniocentesis may be done later in pregnancy to see if the baby's lungs are mature enough for the baby to breathe well after birth. This is usually done if the mother has a high-risk condition and the baby needs an early delivery. Amniocentesis can also be used to check for an infection in the amniotic fluid.

What preparation is needed for amniocentesis?

Since it is done under ultrasound guidance, it helps to have a full bladder. Drink a lot of water or avoid urinating before the procedure. Follow any other instructions given by the doctor.

What happens during the procedure?

The baby's heart rate is checked before and after the procedure. The mother’s abdomen is cleaned with an antiseptic. The skin may be numbed with an injection of a local anaesthetic.

Ultrasound helps to guide the needle through the abdomen and uterus, away from the baby and to the area where the most amniotic fluid is. A small amount of fluid is withdrawn and sent to the lab for tests.

What happens after the procedure?

The mother and baby are monitored for some time after the procedure before being sent home. Rest is advised for 24 hours after the procedure. The results of the genetic analysis are available in 1 to 3 weeks. Lung maturity can be determined in 1 or 2 days. The results of a test for infection will be available in 1 to 2 days.

What are the benefits of this procedure?

Amniocentesis helps detect genetic problems, such as Down’s syndrome or other chromosomal abnormalities. It can detect development disorders such as spina bifida (a defect of the spine). An infection in the amniotic fluid could be detected by amniocentesis. It can check the maturity of the baby's lungs.

What are the associated risks?

Amniocentesis is a very safe procedure. The risk of complications from this procedure is very low (less than 1% of cases). The possible complications include excessive loss of blood, infection in the amniotic fluid, harm to the baby from the needle, harm to the placenta or cord from the needle, premature breaking (rupture) of the amniotic sac, premature labour, or contractions that can cause labour or miscarriage.