An obstetric ultrasound scan is an important part of adequate ante-natal monitoring.
It confirms the diagnosis and location of the pregnancy, allowing the well-being of the embryo/foetus to be identified.
In cases of risk pregnancy, this ultrasound is essential, as it shows the position of the placenta, its development and the amount of amniotic fluid. It also measures blood flow.
During pregnancy, 3 to 4 ultrasound scans are recommended:
1ST ULTRASOUND: This should be performed between weeks 8 and 12, with the following objectives:
Confirm the pregnancy.
Locate the gestational sac.
Identify the yolk sac and embryo.
Determine the number of embryos.
During this time, the foetus looks like a ‘bean’. The scan can identify the cranial end (head) and caudal end, the morphology of the head (presence or absence), foetal and heart well-being and the tiny limb buds of the embryo, or even the limbs themselves.
After 10 weeks, the nuchal translucency (NT) can be identified and measured; typically, the NT is not visualised. Normal values are below 30 mm (3 cm).
2ND ULTRASOUND: This is called a morphology ultrasound and should be performed between weeks 18 and 12, with the following objectives:
Thoroughly assess foetal structures and the absence of morphological abnormalities.
Observe and analyse the cranial portion of the foetus, its facial profile, the four chambers of the heart and the great vessels, the stomach, kidneys, bladder, the attachment point of the umbilical cord to the abdomen and the limbs; the location of the placenta must also be assessed.
3RD ULTRASOUND: This should be performed between weeks 30 and 34, with the following objectives:
Determine the position of the foetus, location of the placenta, volume of amniotic fluid and expected foetal weight.