An expert's guide to third trimester ultrasounds

Third trimester ultrasounds are an important step in pregnancy, reassuring the mother that her baby is growing healthily. In his latest online article, highly-experienced consultant in obstetrics and maternal and foetal medicine Dr Spyros Bakalis explains this scan in detail.

What exactly is a third trimester ultrasound scan?

A third-trimester ultrasound scan is a scan that takes place between 24 weeks and 42 weeks of pregnancy. The aim of the scan is to measure the size of the baby by measuring the head circumference, abdominal circumference and femur length.

The scan also allows us to review the blood flows of the baby, which flow from the baby to the placenta and back again, and to also check the amniotic fluid of the baby. These parameters allow us to reassure a mother that the baby is growing well and have we have no concerns regarding the placenta.

In addition to this, it allows us to review some of the baby's anatomy, specifically the brain, the kidneys and the bowel. Finally, if the baby's posing, it allows us to give the mother a good picture of her baby.

When is it necessary?

The third trimester scan is necessary when there are concerns regarding the baby's growth, or the movements of the baby.

In addition, in routine pregnancies which have no other complications, it is by far the best way to get a good estimate of the baby's weight and to ensure the baby is growing, and not suffering any complications in the womb.

Can you detail what exactly this third trimester ultrasound shows?

The third trimester ultrasound shows us the estimated weight of the baby. This allows us to plot the baby's weight on a chart and ensure the baby is growing appropriately. If there are any concerns about the baby's weight, it may make us reconsider delivery plans for the baby and mother.

How long does it usually take?

The third trimester ultrasound usually takes between 10 and 20 minutes.

How safe is it?

Ultrasounds are considered safe during pregnancy. Long-term studies do not show any complications for babies who are exposed to ultrasounds.

What should pregnant women be aware of before going for a third trimester ultrasound?

The vast majority of third trimester ultrasounds are uncomplicated, without any concerns regarding the baby. However, women need to be aware that occasionally we find a size change in the baby which may change management options for her pregnancy.

Secondly, women need to be aware that occasionally we do find a foetal abnormality which needs to be discussed further with the mother.

Dr Spyros Bakalis is a renowned consultant in obstetrics and maternal and foetal medicine. If you would like to book a consultation with Dr Spyros Bakalis you can do so today via his Top Doctors profile.