Amniocentesis & CVS: is it safe?
Amniocentesis and chorionic villus sampling (CVS) are tests that give a definite answer about your baby's chromosomes and, when needed, specific genetic conditions. Many parents worry about safety. In experienced hands, the risk is much lower than most people think.
Why are they offered?
- A high-risk result on combined screening or NIPT.
- A finding on the NT or anomaly scan.
- A previous baby, or a family member, with a chromosomal or genetic condition.
- Parents known to carry a genetic condition, such as thalassaemia.
Screening tests estimate a chance. Only these diagnostic tests can confirm or rule out a condition.
CVS (chorionic villus sampling)
CVS is done at 11–14 weeks. Under continuous ultrasound guidance, a fine needle passes through the abdomen to take a tiny sample of the developing placenta (chorionic villi), which has the same genetic make-up as the baby. Its main advantage is an earlier result.
Amniocentesis
Amniocentesis is done from 15–16 weeks onwards. A fine needle, guided by ultrasound, takes about 15–20 ml of the fluid around the baby, which contains the baby's cells. The body replaces this fluid within hours.
Is it safe? The real risk
Large recent studies show that the extra risk of miscarriage from amniocentesis or CVS, when done by a trained specialist, is very small: about 0.1–0.5% (1 in 200 to 1 in 1,000), and in some studies hardly different from women who did not have the test. The older figure of "1 in 100" is now considered outdated. The risk is lowest when the procedure is done by a fetal medicine specialist who performs it regularly.
Other uncommon issues include mild cramping, a little bleeding or fluid leakage, and rarely infection. If you are Rh-negative, you will be given anti-D injection.
Does it hurt?
Most women say it feels like a blood test or a short period-like cramp. The needle is in place for less than a minute, and the whole procedure takes only a few minutes.
Results
- Rapid test (QF-PCR / FISH): results for common conditions such as Down syndrome in about 2–3 days.
- Full karyotype or chromosomal microarray: usually 2–3 weeks.
- Specific genetic tests, if needed, are discussed in genetic counselling.
Aftercare
Rest for the remainder of the day and avoid heavy lifting for a day or two. Normal activities can usually be resumed the next day. Contact your doctor if you have fever, heavy bleeding, fluid leakage or severe pain.
Have questions about your pregnancy?
Book a consultation with Dr. Sushma Dhakal, Fellowship-trained fetal medicine specialist (FMF UK certified).
Frequently asked questions
What is the miscarriage risk of amniocentesis?
With an experienced specialist the added risk is very small, about 0.1–0.5% (1 in 200 to 1 in 1,000) or less.
When are CVS and amniocentesis done?
CVS at 11–14 weeks; amniocentesis from 15–16 weeks onwards.
Does amniocentesis hurt?
Most women describe it as similar to a blood test or a short cramp. It lasts only a few minutes.
How long do results take?
Rapid results in about 2–3 days; full chromosome analysis usually in 2–3 weeks.
This guide is for general information only and is not a substitute for personal medical advice. Every pregnancy is different. Please consult your doctor about your own situation. In an emergency, go to the nearest hospital.
All guides
- What is an NT scan? A guide to the 11–14 week scan
- The anomaly (level II) scan: your 18–22 week detailed scan
- Growth & Doppler scans and IUGR (fetal growth restriction)
- Genetic counselling in pregnancy: who needs it and what happens
- Early pregnancy (dating) scan at 6–10 weeks: what to expect
- Fetal echocardiography: a detailed scan of your baby's heart
- Third-trimester well-being scan and biophysical profile (BPP)
- NIPT vs combined screening: which test is right for you?
- Twin pregnancy scans: chorionicity, TTTS and how often to scan
- Cervical length scan and preterm birth risk
- Fetal neurosonogram: a detailed scan of your baby's brain and spine