Desert Storks

Amniocentesis

Amniocentesis is a medical procedure performed on a pregnant woman to withdraw a small amount of amniotic fluid from the sac surrounding the foetus. By about the 16th week of pregnancy, the developing baby is suspended in around 130ml of amniotic fluid, which the baby constantly swallows and excretes. The goal of amniocentesis is to examine a tiny amount of this fluid to obtain information about the baby - including its sex - and to detect physical abnormalities such as Down’s syndrome or spina bifida. Amniocentesis is only performed on women thought to be at higher risk of delivering a child with a birth defect.

Problems detected by amniocentesis
Amniocentesis can detect a number of disorders that will affect babies, while they are still a small foetus in the uterus. These conditions include:

Down’s syndrome.

Neural tube defects, such as spina bifida.

Cystic fibrosis.

Genetic disorders - amniotic fluid samples can be DNA tested to identify a wide range of genetic disorders, including Fragile X syndrome, phenylketonuria, Tay-Sachs disease and sickle cell disease.

Medical issues to consider
As a woman grows older, the risk of having a child with Down’s syndrome begins to increase significantly - from about one in 2,000 (at age 20 years) to one in 100 (at 40 years). Pregnant women who may be candidates for amniocentesis include:

Women over the age of 40 years (Victorian women aged 37 years and over are routinely offered this test).

Women with a family history of chromosomal abnormalities, such as Down’s syndrome.

Women who have already had children with chromosomal abnormalities.

Women known to be carriers of genetic diseases.

Women with partners who have a family history of a genetic disorder or chromosomal abnormality.

Women who return an abnormal ’serum screen’ blood test or ultrasound examination result.

The procedure
Before having amniocentesis, it is usual for the woman and her partner to be counselled on the risks of the procedure. Amniocentesis is performed between 16 and 20 weeks into the pregnancy. The woman lies down, and the position of the foetus and the placenta are determined by an ultrasound scan. When the doctor is sure of a safe spot, they swab the woman’s belly with antiseptic and inject a local anaesthetic into the skin. Using a long, thin needle, the doctor extracts about 15 to 20ml (approximately three teaspoons) of amniotic fluid. This takes about 30 seconds or so. The foetus is checked afterwards to make sure all is well. The entire procedure can take around 90 minutes.

Immediately after the procedure
You may need to wait in the surgery for around 20 minutes before leaving for home. Most patients find amniocentesis to be painless, although it is recommended to continue resting for an hour or so afterwards. The doctor will advise when the results are expected. In some cases, the results may take up to three weeks. Side effects of the procedure may include:

Mild discomfort

Slight bruising at the injection site.

Possible complications
While amniocentesis is generally considered a safe procedure, possible complications may include:

Infection - symptoms of which include high fever. Contact your doctor immediately.

Vaginal leakage - amniotic fluid may leak from the vagina in about one per cent of cases. Contact your doctor for reassurance. In most cases, the leakage slows and stops within two days or so.

Spontaneous abortion - can occur in less than one per cent of women undergoing this test. Exact figures are hard to calculate, since some miscarriages would have happened anyway - with or without the amniocentesis.

Injury to the baby - very rarely, the needle used during the procedure may accidentally touch some part of the baby’s body.

Taking care of yourself at home
Most women feel fine after the procedure, and no alteration to normal routine is necessary. However, it is generally advised to take it easy for the next couple of days.

Long term outlook
Amniocentesis rarely causes harm to either the mother or her baby in the long term. Complications following amniocentesis are very rare, but if you experience unusual symptoms, such as losing blood vaginally, seek medical attention promptly.

Where to get help

Your doctor

Gynaecologist.

Things to remember

Amniocentesis is a medical procedure performed on a pregnant woman to withdraw a small amount of amniotic fluid from the sac surrounding the foetus.

The goal of amniocentesis is to examine a tiny amount of this fluid to obtain information about the baby, including its sex, and to detect physical abnormalities such as Down’s syndrome or spina bifida.

Amniocentesis is only performed on women thought to be at higher risk of delivering a child with a birth defect.