Addressing your concerns
Diagnostic tests: results and risks
Chorionic villus sampling (CVS) involves taking a small sample from the placenta, after 11 weeks. The risk of this causing a miscarriage is about 1 in 100–200. Limb abnormalities have been reported in babies who underwent CVS before 10 weeks, so we never offer CVS before 11 weeks’ gestation. Results are usually available within 10 days.
Amniocentesis involves taking a small amount of amniotic fluid from around the baby. The risk of miscarriage is about 1 in 200. This is done from 16 weeks and results are usually available within 2–3 weeks.
Provisional results on both tests within 36–48 hours can be obtained using special techniques (PCR and FISH), and this can be discussed if you wish.
Should you have the triple test too?
An alternative screening test for Down’s syndrome is the blood test performed at 15–18 weeks of pregnancy, known as the triple test. This is available on the NHS in Oxford but is less accurate than a Nuchal scan with combined blood tests, so you should not have this test too – you are likely to receive a different risk with each test and conflicting results will cause confusion and result in too many people having an unnecessary diagnostic test.
One blood test which forms part of the triple test is AFP, which is also used to screen for babies with spina bifida. This abnormality is not usually identifiable at a Nuchal scan, but is normally visible by a later ultrasound. The AFP test is occasionally helpful in identifying women who require a 16 week scan to look at the baby’s spine. If you have had a Nuchal scan you can still have the AFP test without having a triple test: this is routinely performed on the NHS in Oxford and can be arranged through your own doctor or midwife.
Who will perform the Nuchal scan?
The scans will be performed by Mr Lawrence Impey or another highly experienced doctor or sonographer. Mr Impey is a Consultant Obstetrician at the John Radcliffe Hospital, Oxford, the director of subspecialty training in fetal and maternal medicine, and a specialist in ultrasound and fetal medicine. We can tell you who will be doing your scan when you book the appointment. We have performed several thousand Nuchal scans, our results are audited both locally and independently and we are happy to discuss our quality assurance if you wish.
Where will the scan be performed?
The scan will be performed in the Feto-Maternal Medicine Unit on Level 6 of the Women’s Centre of the John Radcliffe Hospital, Oxford (see map of the hospital and surrounding town). Car parking is available but on a weekday, it may take some time to find a place.
What about the nasal bone?
Recent research shows that most fetuses with Down’s Syndrome do not have a nasal bone that is visible at the Nuchal scan. The presence or absence of the nasal bone, therefore, can be used to adjust the risk that you are given if you have a ‘borderline risk’, between 1 in 100 and 1 in 300. Unfortunately, assessment can be extremely difficult and if so, may require considerable extra time: if not performed properly, nasal bone scanning is misleading. Mr Impey is experienced and fully accredited to perform nasal bone scanning, but if we are to give you an accurate risk which includes nasal bone assessment, we may sometimes need to perform a second scan, and you will unfortunately incur extra cost for this.
To get advice
We recommend that you discuss your options with your midwife, general practitioner or obstetrician. More information on nuchal translucency scanning can also be obtained online from The Fetal Medicine Foundation.
Research
The department is actively involved in research and you may be asked if you would like to participate. If you do not wish to take part, the quality of your care will not be affected in any way.