Why have a late pregnancy ultrasound after 26 weeks?

Late ultrasounds are performed to assess the growth and health of the baby. Some doctors will order this routinely at around 32 weeks. Others only if there are medical complications such as bleeding or where there is a suspicion that the baby is smaller or larger than expected. The weight of the baby can be estimated from the measurements taken at this time and the health is assessed by measurement of the amount of fluid around the baby (amniotic fluid index), the movements of the baby and measurements of blood flow between the placenta and baby (umbilical artery blood flow studies).

The lie of the baby is assessed (either head up or head down) and the anatomy is checked again. The placenta position is assessed. Often in late pregnancy images of the baby are not as clear as that at 13 and 20 weeks. Often the baby is face down and other structures tend to be obscured by the limbs.

You might get additional scans in your third trimester if:

  • Your baby isn't moving as well or as often as he should be
  • Your baby is in the breech, oblique or transverse position
  • You are carrying twins or more
  • The umbilical cord was seen to be around your baby's neck in an earlier scan
  • the amount of amniotic fluid is more or less than it should be
  • your baby feels smaller or larger than expected for her gestational age

Can you see the placenta's position on late pregnancy scans?

The position of the placenta is checked.  1 in 100 placentas are low at 32 weeks. Transvaginal ultrasound may be required during your third trimester ultrasound if there are concerns about the position of the placenta, to get a better look at the cervix area and lower edge of the placenta.

How Long will the scan take?

A growth scan typically takes 30 minutes to complete. Occasionally we can’t see/scan everything because of your baby’s position or the position of your placenta. Your own BMI also affects how well we can see your baby on ultrasound. 

How do I prepare for the scan?

There is no preparation for a late pregnancy scan, although it is always helpful to have a partially filled bladder.