The 11-13 weeks scan (or nuchal translucency scan) was initiated in the mid 1990s with the scope of measuring the nuchal translucency in order to calculate the risk for Down syndrome. Over the years the examination evolved to the extent that it is now a detailed check of the fetus as well as a first assessment tool for severe pregnancy complications.

Nowadays the 11-13 weeks scan provides valuable information such as:

1. Dating the pregnancy.
This is particularly important if the mother is unsure of her last period, if she does not have a regular 28-days cycle or if there was a recent pregnancy. In those cases the dating of the pregnancy relies on the measurement of the length of the fetus (crown-rump-length, CRL).

2. Calculating the risk for three important chromosomal abnormalities: Trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome) and trisomy 13 (Patau syndrome).
By combining maternal age with ultrasound features (most importantly the nuchal fluid) and biochemical markers (placental hormones circulating in the blood of the mother) special mathematical models can compute the personalised risk of the fetus to have one of those three conditions.
The nuchal translucency, the fluid accumulating in the back of the neck of the fetus at this particular period of the pregnancy, is a key measurement. The excessive amount of fluid has been correlated with a number of structural abnormalities, chromosomal abnormalities and genetic syndromes. Therefore the fetus with more fluid needs follow up by a specialist.

3. Checking the organs of the fetus.
An integral part of the 11-13 weeks ultrasound scan is the examination of the fetal anatomy. By performing a detailed, methodical check of the fetal organs/systems (brain, heart, stomach, bladder, spine and limbs) we can diagnose about half of the major structural anomalies.

4. Calculating the risk of serious complications of the pregnancy.
The interrogation of the blood supply to the arteries of the womb combined with the maternal blood pressure and the measurement of a specific placental hormone (PlGF) allows the calculation of the risk for severe pre-eclampsia and/or fetal growth deficiency. Pregnant women at high risk are advised to take aspirin for the duration of the pregnancy.
The measurement of the length of the cervix (the neck of the womb) identifies a small group of women with very short cervix. These women need intensive follow up because of the increased risk of preterm delivery.
This important examination, the 11-13 weeks scan, should be carried out by trained and certified doctors, committed to ongoing education and auditing (