An amniocentesis is an ultrasound guided procedure which is performed to obtain a sample of amniotic fluid. The amniotic fluid surrounds the baby and both are contained within the amniotic sac. The amniotic fluid contains cells shed from the baby’s skin, lungs and bladder. An amniocentesis is best performed after 15 to 16 weeks of gestation.
- If you have received a screen positive result on the NIPS (cell free DNA) screening.
- If on ultrasound an increased nuchal translucency was detected (greater than 2.5mm.
- If you have received an increased combined first trimester screening result for Trisomy 21(Down syndrome), Trisomy 18 (Edward’s syndrome) or Trisomy 13 (Patau syndrome).
- If any abnormality has been detected on ultrasound.
- If you have previously had a child with a chromosomal abnormality or birth defect.
- If there is a family history of genetic disease.
- If your requesting doctor has referred you for any other reason.
- If you are 35 years or older at the time of delivery, there is an increased risk of chromosomal abnormalities.
Prior to the amniocentesis being performed, an ultrasound is done to check that the baby’s heart beat can be seen clearly and the position of the baby is suitable for the sample to be collected. When the correct site is detected, our Doctor will clean the site with antiseptic and small amount of local anaesthetic will be injected.
The local anaesthetic is not necessary for the procedure, however, it does ensure that the procedure is performed with as much comfort as possible. Still under ultrasound guidance, a fine needle is inserted and guided into the amniotic sac and approximately 15-20mls of amniotic fluid is withdrawn.
After the procedure ourDoctor will perform another ultrasound to show you your baby’s movement and heartbeat.Very occasionally, the Doctor is unable to obtain enough amniotic fluid on the first attempt, or is unable to collect a sample due to other reasons. If this happens, another sample may be required. This second sample may be performed at the same appointment or rescheduled for another day depending on the reason why the test was unable to be performed.
Although the amniocentesis is a relatively safe procedure there is still the risk of miscarriage. This risk of miscarriage is about 1:500 – 1:1,000*. If miscarriage is caused by the procedure, this usually occurs within 2 weeks of the procedure.Temporary leaking of the amniotic fluid after an amniocentesis can occur occasionally.
A little bit of cramping or spotting can occur after the procedure, but if there is severe cramping, bleeding or fluid loss, then please contact your referring Doctor or our practice and a follow up ultrasound will be arranged to check the pregnancy. Women with a Rhesus negative blood group may require an injection of anti-D post procedure, to protect a woman from developing antibodies against the fetus whose blood group may be Rhesus positive.
The amniotic fluid collected at the procedure is sent to a laboratory for either a banded karyotype analysis or micro-array molecular karyotype analysis. The cells from the specimen are harvested and cultured and provide us with detailed genetic information about your baby.
Please feel free to discuss these options with one of our Genetic Counsellors.
The results of an amniocentesis are the most accurate of all diagnostic testing. Despite all care, human or laboratory errors can occur, so results are never foolproof.
No. Despite so many advances in genetic testing there are still many abnormalities that are not detected. Most major chromosomal abnormalities can be detected and now with the microarray testing being available we are able to detect many more genetic conditions that are caused by either extra or missing segments of DNA.
There are also structural abnormalities that may be detected which are not genetically related.
Please feel free to discuss the testing options with one of our Genetic Counsellors or the Doctor performing your procedure.
Once the sample arrives at the laboratory the cells are cultured (grown under controlled conditions), analysed and then reported. Both the full karyotype or full molecular karyotype are available in around 7 to 10working days.
The laboratory do offer a rapid result which is called aFISH (Fluorescent In Situ Hybridisation). The FISH test analyses for Down Syndrome (Trisomy 21), Edward’sSyndrome (Trisomy 18), Patau Syndrome (Trisomy 13), (22q deletion), DiGeorge Syndrome and any anomalies with the sex chromosomes (X and Y).
The FISH results are usually available with 24-48 hours, however, the laboratory do charge an additional fee for the FISH test,please discuss this with the Genetic Counsellor orDoctor prior to the procedure.
There is no physical preparation required for amniocentesis. However, it is important to have a copy of your blood group with you on the day of the test. Women who have a Rh negative blood group require an injection of Anti-D after the procedure. Anti-D can prevent the mother’s antibodies crossing the placenta and damaging the baby’s red blood cells.
It is recommended that you have someone to drive you home after your procedure. You should rest for about48 hours after the procedure. It isn’t necessary to have complete bed rest, but any lifting or strenuous exercise is to be avoided.
Medical certificates can be arranged for both you and your partner if you require time off from work or study. Slight cramping and possible spotting is not uncommon after the procedure. If you start to experience any severe cramping or there is excessive fluid loss you should contact your Doctor.
Our Genetic Counsellor will work very closely with you and your referring Doctor to ensure you are supported through any abnormal result. We will provide you with as much information about all options available to you.