Chorionic villus sampling and amniocentesis
Chorionic villus sampling (CVS) and amniocentesis are diagnostic tests that can be undertaken during pregnancy. These tests may be offered under the following circumstances:
- If you have a higher chance result for Down syndrome, Edwards syndrome or Patau syndrome
- If you are at higher risk of passing on an inherited condition to your baby, such as cystic fibrosis, sickle cell disease or thalassaemia major
- If you had a previous pregnancy where your baby had a genetic or chromosomal abnormality
- If a significant fetal abnormality is seen on a scan
- If there are any other clinical indications
CVS
- Performed from 11 weeks of pregnancy onwards
- A sample of placenta is taken
- 1% risk of procedure-related miscarriage at this hospital (national risk is 1–2%)
Aminocentesis
- Performed from 16 weeks of pregnancy onwards
- A sample of amniotic fluid is taken
- 0.5% risk of procedure-related miscarriage at this hospital (national risk is 1%)
For both tests, there is a less than 1% chance of obtaining an unsuitable sample or unclear result. If this occurs, we will discuss your options and make an appropriate plan based on your individual circumstances.
The doctor will discuss the test with you prior to the procedure and perform a scan to check that it is clinically appropriate to proceed. Both tests take approximately 3–4 minutes, although your entire appointment will last 20–30 minutes. During the procedure, under ultrasound guidance, a needle is passed through your abdomen into the uterus, and a sample is taken.
If your blood group is rhesus negative, you may require an injection of Anti-D following either procedure. After the procedure, it is recommended that you rest for the remainder of the day. You may experience some abdominal discomfort; it is safe to take paracetamol in these circumstances.
The sample is sent to the laboratory for a rapid test (QF-PCR), which checks for the three most common chromosomal abnormalities: Down syndrome, Edwards syndrome and Patau syndrome. In specific clinical cases, the test may also check for Turner syndrome. Results are usually available within 4 working days. Once we receive the information, we will contact you by telephone and plan your ongoing care.
If you have a higher chance screening result or request a diagnostic test without clinical indication, only a QF-PCR test will be performed on the sample.
CVS and amniocentesis do not detect structural abnormalities. Therefore, we recommend a scan between 18 and 21 weeks of pregnancy, regardless of the results of the diagnostic test.
In certain clinical cases, further testing will be undertaken on the sample. This will be discussed with you before the procedure.
| Test | Indication | Method | Timeframe |
|---|---|---|---|
| DNA Analysis | Known risk of specific genetic disorder | DNA from fetal cells is examined to determine if the baby has the known genetic disorder. The type of test will depend on the specific disorder. | Dependant on specific test |
| Full karyotype | Abnormal rapid test result / other indication | Examines all 23 pairs of chromosomes under a microscope to identify any extra or missing whole chromosomes, translocations or large segment imbalances. This test does not detect gene mutations and may not identify small segment imbalances or mosaicism. | 10–21 days |
| Array CGH | Significant fetal abnormality on ultrasound | Screens all 23 pairs of chromosomes and can detect very small changes, such as gains and/or losses of chromosome material that cannot be seen under a microscope. This test does not detect balanced chromosome rearrangements or gene mutations and may not identify some small imbalances or mosaicism. | 10–21 days |
All results will be communicated and discussed with you as soon as they are received, and follow-up will be arranged as appropriate. In some cases, it may be necessary to take parental blood samples to help interpret the results. If this is required, you will be informed and asked to attend for a blood test as soon as possible.
If you have any questions or concerns, please contact the specialist midwives:
- Chelsea and Westminster: 020 3315 5874
- West Middlesex: 020 8321 6727/5016
If you have a medical concern outside of office hours, please contact the maternity helpline:
- Chelsea and Westminster: 020 3315 6000
- West Middlesex: 020 8321 5839
Alternatively, go to your nearest A&E.