Third Trimester Scan

For most parents the 19 week scan becomes an important stage of reassurance that their pregnancy is progressing normally. It can also be a really motivating reward for the less pleasant aspects of pregnancy.

Parents find seeing the active foetus helpful, as it is normal not to be feeling movements in mid-pregnancy, despite how often you are asked about it! Unlike the first trimester, you may not have symptoms to “remind” you that the pregnancy is going well.

The 19 week ultrasound can check for problems which may be able to determine what is safest for your pregnancy.

Some conditions can be managed during pregnancy better if they are detected. Some problems in the foetus are relatively subtle in appearance but can indicate an emergency at birth. This means that the delivery of the baby will need to be well coordinated. Other problems do not trouble the foetus in utero, but are not compatible with survival after birth.  

• Fetal position.
• Fetal size: an estimated fetal weight is calculated from measuring the fetal head, abdomen and femur. 
• The weight ‘estimate’ is truly that, with one standard deviation being 15% either side of the true weight.
• Some assessment of fetal anatomy: bearing in mind, late pregnancy limits the views and the check will not generally be a universal check, like the 19-week ultrasound.
• Placental position and maturity.
• Amniotic fluid volume.
• The Doppler blood flow in the umbilical cord and the brain. This gives an idea of the placental function and reserve.
• Fetal movements.
• Other factors that are requested by the referring doctor.

Your doctor might suggest you to undergo a third semester scan after 28 weeks. Also known as “late pregnancy” scan, this ultrasound help your doctor assess the health of your baby, especially if you have a medical condition that might affect fetal growth.

The objective of a third trimester scan is to assess the overall growth and well-being of the fetus, especially for women with high-risk pregnancies.This late ultrasound help assess the fetal weight and position, as well as the movements and placenta maturity.

During your third trimester, if you have a healthy pregnancy, you might not require any late ultrasound. However, if you are a woman with high-risk pregnancy, or any anormalities were detected during previous routine ultrasounds, you might need more.

Most women will be advised to have at least two ultrasound scans during their pregnancy, the first and second trimester scans. However, depending on your medical conditions and the results of the first ultrasounds, you might require additional scan.