What is a Nuchal Scan?
It is a type of ultrasound scan that is carried out from 11 weeks + 3 days to 13 weeks + 6 days. The scan is usually performed transabdominally but in a few cases, it may be necessary to do the examination transvaginally. This is one of the most important scans during pregnancy and is recommended for all women.
What Are the Aims of the Nuchal Scan?
- To date the pregnancy accurately: This is particularly relevant for women who cannot recall the date of their last period, have an irregular menstrual cycle, or have conceived whilst breastfeeding or soon after stopping the pill. We measure the size of the fetus and from this, we calculate the expected date of delivery.
- To diagnose multiple pregnancies: Approximately 2% of natural conceptions and 10% of assisted conceptions result in multiple pregnancies. Ultrasound scanning can determine if both babies are developing normally and if the babies share the same placenta which can lead to problems in the pregnancy. In such cases, it would be advisable to monitor the pregnancy more closely.
- To diagnose major fetal abnormalities: Some major abnormalities may be visible at this gestation. However, it will still be necessary to have a 20-week anomaly scan.
- To diagnose early miscarriage: Unfortunately, in 2% of women who attend for a nuchal scan, it is found that the fetus has died, often several weeks before and without any warning. Couples will receive full counseling as to the possible causes of this problem and the options for subsequent measures that may be necessary.
- To assess the chance of Down’s syndrome and other chromosomal conditions:
- Each woman will be given an estimate of her chance of having a chromosomal condition present for this pregnancy. The conditions that the nuchal scan checks for are Down’s Syndrome, Edwards’ Syndrome, and Patau’s Syndrome. This is calculated by taking into account the age of the mother, fetal heart rate measurement, measurement of two hormones in the mother’s blood (free ß-hCG and PAPP-A), and the scan findings of nuchal translucency thickness (measurement of the fluid present behind the baby’s neck), nasal bone, blood flow through the fetal heart and ductus venous and fetal abnormalities. Our nuchal scan has a sensitivity of 95% for detecting Down syndrome and is more extensive than what is routinely offered by the NHS. Parents will receive full counseling concerning the significance of these changes and the various options for further investigations including invasive testing or the NIPT.
What if My Nuchal Translucency Scan Result Shows an Increased Chance of the Presence of a Chromosomal Condition?
The nuchal translucency scan is a screening test which means that this test can only give a probability for a condition being present. It is not a diagnostic test and thereby it cannot confirm if a chromosomal condition is present or absent. If your nuchal scan screening shows an increased chance, then we will provide you with recommendations for further screening or invasive testing such as a CVS or amniocentesis.
What Is the Next Scan That I Should Have After the Nuchal Scan?
If your nuchal scan screening shows a low probability, then the next scan that is recommended is the anomaly scan.
