Amniocentesis
Amniocentesis is usually done around the 16th week of pregnancy, but can be performed later. Under ultrasound guidance, a fine needle is passed through the mother’s abdomen into the uterus and a small sample of amniotic fluid surrounding the baby is collected. The fluid contains cells from the baby which can be grown in culture in a laboratory and used to look at the baby’s chromosomes. Occasionally the fluid may be tested for a particular problem such as in infection.
Most women do not describe the procedure as painful but it can feel uncomfortable and it is not unusual to feel some period-like cramping pains afterwards. It is a good idea to take it easy for 48 hours after the procedure and avoid strenuous physical activity such as heavy lifting.
Amniocentesis results
Rapid results
Q-PCR and FISH are molecular tests that can be performed on the sample to provide a rapid but accurate diagnosis of Down’s syndrome and two other rare but serious chromosomal syndromes called Patau’s and Edwards syndromes. Results take on average three working days. All hospitals can offer this service through the laboratories they use, but some will ask you to pay a fee.
Full karyotype
A full karyotype means the laboratory use cells from the sample to look at all the baby’s chromosomes under a microscope. They check for any major changes in the chromosomes and can tell the baby’s sex. It is a longer process than the rapid tests and so results can take up to three weeks.
Very occasionally the sample of amniotic fluid taken cannot be used by the laboratory to obtain an accurate result. If this happens you will be offered a repeat procedure.
Why do some women miscarry after amniocentesis?
Approximately one out of every 150 women who has an amniocentesis will have a miscarriage. It is difficult to give a definite reason why this happens.
Most of those few women who have a miscarriage due to the procedure have it fairly soon afterwards, within around 72 hours. There is still a risk of miscarriage after this and up to two weeks after the amniocentesis, but it is extremely unlikely to happen.
If the health professional performing the procedure is skilled at doing it, this can help to minimise the risk. This skill comes with experience so you can ask how often the doctor who is going to do your amniocentesis does the procedure. The Royal College of Obstetricians and Gynaecologists recommends that a health care professional should do at least ten procedures a year to retain his or her competency.