All pregnant women are offered a nuchal scan between 11 weeks +3 days to 13 weeks +6 days of pregnancy, to help screen for the most common chromosomal conditions like Down’s syndrome, Edward’s syndrome and Patau’s syndrome.
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 who 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 counselling 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 individual 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 considering 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 venosus and fetal abnormalities. Parents will receive full counselling concerning the significance of these chances and the various options for further investigations including the procedures.
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 of further screening or invasive testing such as a CVS or amniocentesis.
