Foetal assessment scans, explained

Posted on 5 February 2019

Seeing your baby for the first time on an ultrasound scan is such a special moment. Plus, you get to take baby’s first pictures home. Dr Lou Pistorius, Ob-Gyn and perinatologist at Mediclinic Panorama, explains the purpose of foetal assessment scans, the ideal time to have them and why they’re important.

“Most expectant mothers have at least two routine ultrasound scans,” Dr Pistorius says.

These are usually the first-trimester screen and the second-trimester scan. They can be performed by your gynaecologist, by a sonographer (who does low-risk screening examinations) or by a sub-specialist, such as Dr Pistorius, who evaluates the baby in greater detail for abnormalities.

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First trimester: 11 to 13 weeks and four days

This scan helps doctors calculate your estimated date of delivery (EDD), checks that your baby is growing and developing normally and diagnoses the type of twin (or other multiple) pregnancy.


It’s important to know whether each twin has its own placenta, or whether they share a common placenta. If they share a placenta, your doctor will monitor your pregnancy more closely. “More importantly, this scan measures the risks for chromosomal abnormalities such as Down’s syndrome and assesses your risk of pre-eclampsia (high blood pressure brought on by pregnancy). This scan can help prevent 80% of cases of early pre-eclampsia,” says Dr Pistorius.

Second trimester: 18 – 23 weeks

Your baby’s entire skeleton can be seen and is checked. This scan aims to determine that all your baby’s organs are in place and growing well. It also helps ascertain the position of the placenta and the amount of amniotic fluid – too much or too little is associated with certain conditions or abnormalities.

Doctors can also measure the length of your cervix to assess the risk of pre-term labour (especially if this is your first pregnancy, or in the case of a previous pre-term delivery) and determine your baby’s gender.

INFOGRAPHIC: Your baby’s first 72 hours 

Specialised scans

If a problem is detected with your baby’s heart or brain, a sub-specialist will do a specialised form of the 20 weeks ultrasound. The foetal echocardiography examines your baby’s heart in more detail and the foetal neuro sonograph examines your baby’s brain in detail. This allows doctors to plan for the care of the baby after delivery. For instance, babies with a heart problem can be safely delivered where there’s a specialised paediatric cardiac unit.

3D and 4D scans

Most expectant moms can have a healthy pregnancy without ever having a 3D or 4D scan. “Generally speaking, 3D and 4D scans are not essential for the evaluation of the baby,” says Dr Pistorius. “However, in some cases when there is a problem with the baby, 3D or 4D scans can help show the parents what the problem is, for example, a cleft lip,” he adds. The scans are usually performed between week 20 – 26.

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Published in Pregnancy

In the interest of our patients, in accordance with SA law and our commitment to expertise, Mediclinic cannot subscribe to the practice of online diagnosis. Please consult a medical professional for specific medical advice. If you have any major concerns, please see your doctor for an assessment. If you have any cause for concern, your GP will be able to direct you to the appropriate specialists.

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