The Nuchal scan is a very important scan in pregnancy. It is carried out when you are 11 to 13 weeks and 6 days pregnant and is usually performed through your abdomen. Very rarely an internal scan will be suggested to complete the scan.
At this stage, your baby will measure about 6 to 7 cm and would fit the palm of your hand! You will notice a huge amount of changes from any previous scans and most likely be amazed by how much detail you can see and how much more developed your baby is at this early stage. From the medical point of view this is also the time we record important information:
Diagnose a multiple pregnancy (twins, triplets, etc…)
Yes, sometimes you may be surprised to find more than one baby! Approximately 2% of natural conceptions and 10% of assisted conceptions result in a multiple pregnancy. If there is more than one baby, it is very important to determine whether they share the same placenta and amniotic sac (the bag baby grows in) or not, as this information will help determine how we should monitor your pregnancy.
Date the pregnancy accurately
We measure your baby/s from head to bottom (crown- rump length or CRL) allowing us to determine your most accurate due date. Your due date will be the date when your pregnancy reaches 40 weeks and will be used to calculate how many weeks pregnant you are at any point during your pregnancy. It doesn’t, however, mean you will deliver on exactly this date as babies are considered full term from 37 to 42 weeks of pregnancy. This is when most babies will be born.
To diagnose major fetal abnormalities
Some of the major fetal defects can be seen even at this early stage. Nobody wishes this to be the case, but if any abnormalities are found, informative and sensitive counselling will be given at the same appointment.
To diagnose missed 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. Options for subsequent treatment that may be necessary and referral to the appropriate services will be arranged.
To screen for major chromosomal anomalies
Most couples would like to know if their baby is affected by a major chromosomal anomaly as soon as possible. The 3 most common of these are Trisomy 21 (Down’s Syndrome), Trisomy 18 (Edward’s Syndrome) and Trisomy 13 (Patau’s Syndrome). The scan may appear normal, but it is still possible for a baby to have one of these conditions which is why screening was developed.
The screening works by measuring the nuchal translucency (fluid at the back of baby’s neck) and combining this information with the mother’s age and a blood test that measures two hormones from the placenta. The result will tell us what the chance is of baby having one of these conditions. As this is a screening and not a diagnostic test, it doesn’t tell you 100% whether baby does or does not have a condition, but we can explain the significance of the results and help you decide whether the result is reassuring enough for you, or if you would like to consider further testing. See below for more information on non-invasive prenatal testing.