It is performed from 11 weeks and 2 days to 14 weeks and 1 day of gestational age (45-84 mm crown-rump length). The examination is usually performed transabdominally but in some cases it may be necessary to have the transvaginal scan.

The reasons for this examination are:

The precise estimation of gestational age. Particularly important for women who have an unstable cycle, they cannot remember the date of their last period, have conceived while breast-feeding or shortly after discontinuing a contraceptive pill. We measure the length of the fetus (CRL) and then calculate the exact gestational age and thus the expected date of delivery.

For the diagnosis of multiple pregnancy. About 2% of spontaneous conceptions and 10% of assisted reproductive pregnancies lead to multiple pregnancies. Ultrasound examination can determine if the fetuses are developing properly and whether these babies share the same placenta which can lead to pregnancy problems. Closer monitoring of pregnancy will be recommended in such cases.

Diagnosis of major fetal abnormalities. Some abnormalities may be detected during this period of pregnancy. It is still necessary though, to have the anomaly scan at 22 weeks.

Diagnosis of early negative cardiac function. Unfortunately, 1.5-2% of women who come for the nuchal translucency scan may find that the fetus has no cardiac function, something that can happen weeks before and without warning. Couples will be given consultation on the possible causes of this event and the options for follow-up and investigation that may be necessary if there are reccurent events.

Assessment of Down syndrome risk and other chromosomal abnormalities. After examining nuchal translucency and considering mother's biochemical markers (β-HCG and PAPP-A), each woman will receive an assessment of her individual risk for this pregnancy. This is calculated by taking into account the age of gestation based on the length of the crown rump length, the thickness of the nuchal translucency, the existence of the nasal bone, the age of the mother, the measurement of two hormones in the mother's blood (β-HCG and PAPP-A), blood flow through the tricuspid valve in the fetal heart and Ductus venosus as well as the possible presence of fetal abnormalities or other markers. Parents will receive full advice on the importance of these risks and the various options for further investigation including invasive procedures (Chorion Villus Sampling - CVS) and non-invasive tests (NIPT).

Measurement of blood flow in the mother's uterine arteries to assess the risk of preeclampsia, fetal growth restriction late at pregnancy. If the mother is at increased risk for the above, a dose of 150mg every evening (OD) is recommended. In addition, there is a recommendation for growth control and Dopplers at 28, 32 and 36 weeks of gestation.