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36 Week Ultrasound

By the time you’re 36 weeks pregnant, it would be unusual if you haven’t already had at least one ultrasound. Dating and screening ultrasounds are common in the first and second trimesters of pregnancy and if there are complications, ultrasounds are recommended more frequently.

An ultrasound at 36 weeks pregnant will show a lot more detail than ultrasounds in early pregnancy. Your baby will be fully formed and almost ready to be born. Depending on the type of ultrasound you have, you’ll be able to see your baby in more detail. Their weight can be estimated, their level of maturity and if their general appearance is consistent with a baby of 36 weeks gestation.

Why would I have an ultrasound when I’m 36 weeks pregnant?

Ultrasounds done late in pregnancy can be helpful to detect or diagnose complications. If there’s any doubt about your baby’s position i.e., they’re in a breech position or lying transverse, an ultrasound can help to diagnose this. Most babies who are in any position other than head down, turn by around 36 weeks or before. If they aren’t positioned with their head down (cephalic) in the final weeks of pregnancy, the chances are getting slimmer that they will turn. Planning for a breech birth takes careful discussion between a mother and her maternity care provider.

If you have had any bleeding, an ultrasound can help to locate the source. If you have a low lying placenta or have placenta praevia, there may be problems with the baby being able to get through your cervix. An ultrasound will give detail on the exact location of the placenta to make sure it isn’t blocking the cervix.

If there’s any concern about your baby’s size or their movements, an ultrasound at 36 weeks will also provide more information about your baby’s health. Sometimes ultrasounds are done simply for reassurance, just to check that all is well with the baby.

If there are concerns about the baby’s size, an ultrasound may be recommended at 36 weeks. In the last few weeks of pregnancy, babies gain a fair amount of weight. This is to provide them with reserves of energy for birth and in the first few weeks. Babies who are small for gestational age (SGA) can need special care when they are born. Planning for the baby’s care is important to reduce the risks of complications.

What does a 36-week ultrasound detect?

A third trimester ultrasound is generally done to make sure the baby is growing as they should be. Though it’s not always possible to find out the cause for growth slowing, an ultrasound can help. Often, the placenta is not working as well as it should be to feed the baby and transfer important nutrients. if there are suspicions about a placental abruption, an ultrasound at 36 weeks pregnant will help to diagnose this as a cause for bleeding and/or pain.

Different types of ultrasounds give different information. A 3-D ultrasound provides three dimensional images of the baby. A 4-D ultrasound creates a video of the baby and surrounding uterus.

How do I prepare for my 36 week pregnant ultrasound?

You don’t need to do anything special other than make sure you’re not lying flat on your back. The weight of a pregnant mother’s uterus can reduce blood flow to the baby, because of pressure being placed on her major blood vessels. The sonographer will help you to get into a comfortable position on your side and use pillows to help support your tummy and back.

Be prepared for the ultrasound to take around 30 minutes. You will not get the results back immediately as the images need to be reviewed by a doctor with special training in interpreting the images.

An ultrasound is also done during other special pregnancy tests such as amniocentesis and chorionic villus sampling. Though routinely, both of these tests are done earlier in pregnancy. An ultrasound during both of these procedures helps to ensure the slender needle which is used is inserted into the right place to minimise risk to the baby.


Ask your maternity care provider if you have any questions about a 36 weeks ultrasound. And make a list of questions to ask the sonographer as well. They may be limited to how much information they can give you but there’s no harm in asking.

Take your partner along with you to the ultrasound. If they’re not available, ask a close friend or family member for support.

Written for Huggies by Jane Barry, Midwife and Child Health Nurse, August 2021.