Third trimester scans

23-40 weeks

Wellbeing/growth scan

This is also called a ‘fetal growth scan’ or a ’wellbeing scan’. During this scan we measure the baby's head, abdomen and limbs, and estimate the baby’s weight. This gives a guide to how big your baby will be at birth. We also look at how the baby is moving, the amount of amniotic fluid, and where the placenta is. It is possible to tell the sex of your baby from this scan, but this becomes more difficult as you approach the end of your pregnancy.

Time needed for the scan: About 20 minutes.

We believe it is very useful to have such a scan at about 36 weeks. This scan is usually only offered by the NHS if there is a complication with the pregnancy.

26-32 weeks

3D/4D scans

A 3D ultrasound scan is a special scan that shows the baby in three dimensions. A 4D scan is a 3D scan with the added dimension of time – as in a film or video – so the baby can be seen to be moving.

3D/4D scans are not usually needed for medical reasons. If the baby has a rare malformation, a 3D/4D scan could provide extra information for medical purposes, but this is rare. Parents may want the scan if they are curious to see their baby's face. If you have a 3D/4D scan, we always do a wellbeing scan first, before trying to view the face or other parts of the body in 4D. It may take some time to get a good view of the baby, so the scan could take 30-60 minutes. If the baby is not in a favourable position you may be asked to go for a walk and return later.

The best time to do a 3D/4D scan is at 26-32 weeks of pregnancy when there is a greater volume of amniotic fluid but when the baby has not yet become too big. It is more difficult to see the face if the baby has its arms or legs in front of the face. The baby can be seen to be moving. Sometimes it is possible to record your baby yawning or stretching. If the scan is to be prolonged, you may be asked to take a break and move around to see if the baby will also move.

The cost of the 3D/4D scan includes a scan report, 3D scan pictures in a colour tone and a DVD with a 20-30 minute recording of the scan.

Time needed for the scan: About 30-60 minutes.