The first trimester ultrasound (often referred to as the early anatomy scan) is performed at 13 weeks in pregnancy. An impressive amount of detail can be examined at this early stage.
The scan includes the following:
- Confirmation of the due date
- Detailed early anatomy of the fetus – including early brain, face, heart, abdomen, spine and limbs
- Nuchal translucency
- Pre-eclampsia risk assessment
- Cervix and ovaries
At 13 weeks, the anatomy of a baby can be assessed in great detail through a combination of trans-abdominal and trans-vaginal scanning. Previously, many fetal anomalies were not suspected or recognised until 21 weeks, however, with a thorough assessment and using the latest ultrasound technology, these anomalies may now be identified at 13 weeks gestation.
The nuchal translucency (NT) of the fetus is identified and measured at this scan providing the fetus is not older than 13 weeks and 6 days. The NT is a collection of fluid between the skin and soft tissue at the back of the fetal neck. It is often increased with Down syndrome and other chromosomal or congenital abnormalities.
There are different options available regarding screening for Down syndrome. By 13 weeks, many people have completed NIPT (non-invasive prenatal testing) however some choose to complete FTCS (first trimester combined screening). FTCS involves combining a blood test with the NT measurement, length of the fetus and the maternal age to provide a risk for Down syndrome. FTCS is not as accurate as NIPT. Some people decline all forms of Down syndrome screening. The NT is always examined as an increased NT does increase the risk of congenital abnormality.
At the time of the 13 week scan, the uterine artery blood flow is measured and contributes to the pre-eclampsia risk assessment. Read more about pre-eclampsia here.
The scan will also examine the placenta, cervix, amniotic fluid volume and the ovaries.
How is the scan performed?
A combination of both trans-abdominal and trans-vaginal scanning is generally required to achieve an optimal examination of the fetus. Vaginal scans during pregnancy are safe and often provide exceptional detail of the developing fetus.