Richmond Practice - What are the benefits of ultrasound in later pregnancy?

What are the benefits of ultrasound in later pregnancy?

By Dr Elisabeth Peregrine, Consultant Obstetrician

Published in Baby Surrey, February/March 2015

All women are routinely offered two ultrasound scans during the first and second trimester of their pregnancy by the NHS. The first scan is an early pregnancy scan (dating scan) around 12 weeks; estimating the date of delivery of the baby. The second scan is an anomaly scan between 18 and 21 weeks; checking for any structural abnormalities of the baby. Some women however also opt for some additional scans privately such as a reassurance scan and/or a  dating scan (between 6 and 10 weeks).

So what are the benefits of having a scan after 24 weeks?
The main reason for scanning after 24 weeks (in the third trimester) is to check the growth of the baby and assess how the placenta is working.

A ‘growth scan’ in the third trimester can assess fetal wellbeing by measuring your baby, measuring the amniotic fluid around your baby and measuring the blood flow through the umbilical cord and fetal brain (fetal dopplers). Together these assess whether the placenta is working well. In addition the scan can confirm which way your baby is lying (confirm the baby is head down) and confirm that the placenta is not lying low in the womb.

Usually we recommend serial growth scans (e.g. at 28, 32 and 36 weeks) in women who are at a higher risk of having a smaller or a larger baby. We would therefore arrange these scans if you have diabetes (before or during pregnancy) as you are more likely to have a bigger baby; or if you have a multiple pregnancy (twins or triplets), have had a smaller baby before or have pre-eclampsia (high blood pressure and protein in your urine) or another medical condition. You may also be asked to have a scan if your baby feels small from feeling your abdomen (measuring the height of the womb) or if there is a reduction in your baby’s movements.

A scan in later pregnancy may also be done to confirm that the placenta has moved up away from the neck of the womb if it was found to be low on the anomaly scan at around 20 weeks.

On a scan after 24 weeks the structures in your baby are not usually seen as clearly as they are at 20 weeks although there are a few rare situations where structural abnormalities in babies may not be apparent until later in pregnancy.

Consult your doctor if:
  • you are in the third trimester and think you are at a higher risk of having a smaller or a larger baby.
  • you are pregnant and think that the baby has been moving less than it had been previously.
  • you are pregnant and the height of the womb is less than it should be on measurement by your midwife.

Elsbeth's Doctors provides private pregnancy care and baby scan services by a multi-disciplinary team of specialists, tailored to your needs. Our consultant gynaecologists and obstetricians offer continuity of care and our patients are assisted in a comfortable and caring environment.

For a same day appointment please contact us on 030 0303 5009 or at For more information visit



Guaranteed 10 min response
(in business hours)

Make an appointment >>