7 things you’ll need to know about an amniocentesis

Would you accept the risks getting an amniocentesis entails? Find out more about this prenatal test.

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A pregnancy can be a joy-filled journey, since you’ll marvel at the first glimpse of your little one through an ultrasound, feel the first kicks, and even learning your baby’s gender.

That said, it can also be a full nine months or so that is filled with anxiety, worries, and what-ifs.

Expectant parents usually go through countless prenatal tests, some compulsory in Singapore, and some that aren’t.

An amniocentesis is one of the options available to expectant women. This in an invasive test where a long, thin needle extracts fluid from the amniotic sac around your foetus. The fluid contains cells shed by your baby during pregnancy, which has vital information about your baby’s health ― such as whether your baby has Down syndrome, or any other chromosomal abnormalities.

One mum, Julie Siew, was offered the option of amniocentesis when she was pregnant with her daughter. “According to my OSCAR scan results, the chances of my daughter having Down syndrome was 1 to 880, which is considered high. I decided not to go for the amniocentesis test because of the risks of miscarriage, plus, I knew that I would keep my baby no matter what the results were.”

The fluid contains cells shed by your baby during pregnancy, which has vital information about your baby’s health.

In case you are put in the difficult position of deciding whether to go for this test, here is the lowdown on vital facts about this procedure.

1. It’s a quick procedure
The procedure takes around 10 minutes, says SmartParents ob-gyn expert Dr Christopher Chong. “Under sterile conditions, a very fine needle is used to go through the mum’s abdomen and through the water bag. Some 20cc of amniotic fluid is withdrawn using a syringe, and care is taken to avoid the placenta and the foetus,” he describes.

After the needle is withdrawn, light pressure is put on the needle site for a couple of minutes, and a plaster will be placed on it. “There is no need for sedation or pain relief as it’s like drawing blood from one’s veins,” he adds. The sample is later sent to the cytogenics lab and you’ll get the results in two to three weeks.

2. It can diagnose chromosomal abnormalities
The gynae usually recommends an amniocentesis when a definite diagnosis is needed, notes Dr Chong. This includes an abnormal screening test result for Down syndrome or other chromosomal abnormalities like muscular dystrophy and Tay Sachs disease, previous family history of chromosomal abnormalities or a neural tube defect, abnormalities in the foetus in a previous pregnancy, or in older mums. “The risk of abnormalities increase with the mum’s age,” Dr Chong says. “For instance, the risk of Down syndrome is 1 in 100 at age 45, and 1 in 50 at age 50.”

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3. It can also determine the gender of your baby

Unlike a regular ultrasound scan where you are fully dependent on the cooperation of your little one to determine his or her gender (“Open your legs, baby!”), an amniocentesis is the most accurate way to determine if it’s a boy or girl. So, if you are going for an amniocentesis, you may want to ask about the gender.

An amniocentesis can also determine the maturity of your baby’s lungs ― you may need to do this test if your baby has a condition that requires him to be born early.

4. An amniocentesis is highly accurate
Dr Chong describes the amniocentesis as the “gold standard” of prenatal tests, since it is 99.4 per cent accurate. You have other options (see point 6), but these aren’t as accurate.

The most common risk is due to a leaking or bursting of the water bag, which can result in a miscarriage.

5. There’s a risk of miscarriage
The most common risk is due to a leaking or bursting of the water bag (amniotic sac), which can result in a miscarriage. Dr Chong says that the risk is about one in 200. Other possible risks include infection or injury to the placenta or foetus, but “these risks are low, and will usually not hurt the mother or the baby,” Dr Chong adds.

6. There are alternatives available
If you’re skittish about going for an amniocentesis because of the risks, note that there are other tests that you can take instead.

While the amniocentesis has the highest accuracy of over 99 percent, there are also blood tests that can give an accuracy of 98 to 99 percent. “These are generally called non-invasive prenatal tests, or NIPT,” Dr Chong explains. “The tests are sent to the US, and it takes 7 working days for the results to be out.”

Other options include chorionic villi sampling, which can be done from 10 weeks, where tissue from the placenta is taken, but there’s a 1 to 2 per cent miscarriage risk. A safer option is OSCAR (One-stop Clinic for Assessment of Risk for Foetal Anomalies) test, to be done between 11 and 14 weeks, which includes a blood test and an ultrasound measurement of the foetal cervical neck thickness and nasal bone ― it will test for Down syndrome with an 80 to 90 per cent accuracy.

7. The results can take up to three weeks
Some parents-to-be will decide whether they want to continue with the pregnancy based on the amniocentesis results. By the way, do note an amniocentesis is usually done after 16 weeks and the deadline for legal abortions is 24 weeks.

Since the test results can take up to three weeks, there may not be time for a legal abortion if the amniocentesis is done after 20 weeks, Dr Chong adds.

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