This leaflet is to help you understand what happens during a mid- trimester (20 week) scan, what tests are completed, and what you need to consider if further tests are recommended for your baby.
Why is a spine evaluation performed during the mid-trimester fetal ultrasound scan (anomaly scan)?
The mid-trimester fetal ultrasound scan, also sometimes called the anatomy scan or 20 weeks ultrasound, is an ultrasound performed between 18–22 weeks of gestational age.
The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) recommends that this ultrasound should be performed as a matter of routine prenatal care.
The function of the ultrasound is to measure the fetus so that growth abnormalities can be recognized early and to assess for congenital malformations. At this stage of the pregnancy, the baby is of sufficient size to allow the sonographer to clearly see individual fetal structures, such as the heart, brain and spine. Congenital spinal abnormalities are among the commonest fetal conditions, with a wide range of severity, from major structural defects (i.e., spina bifida) to minor, subtle conditions which may not always be detectable on ultrasonography. However, a mid-trimester scan is aimed at detecting common major spinal abnormalities that can potentially have significant clinical implications for the baby. Timely detection of these conditions can provide adequate time for a detailed workup and management to optimise care for these babies.
How is the spine evaluation performed?
During the routine anomaly scan the spine of the baby will be examined. The evaluation of the fetal spine is a fundamental part of the central nervous system (CNS) scan. Neural tube defects, such as spina bifida, are the most frequent CNS malformations and amount to about 1–2 cases per 1000 births.
A satisfactory examination of the fetal spine requires expertise and meticulous scanning, and the results are heavily dependent upon fetal position.
What happens if there is suspicion of spine malformation?
If during the scan any suspicious finding is seen, the person performing the scan may refer you to a specialist. A detailed, specific evaluation of the fetal spine is not part of the basic examination, although transverse and sagittal views are usually informative. Other views of the fetal spine may identify other spinal malformations, including vertebral abnormalities and absence of the tip of the spine (sacral agenesis). Further imaging, including the use of Magnetic Resonance Imaging
(MRI) can also be suggested based on a detailed examination with a specialist, to rule out other rare spinal abnormalities.
What other questions should I ask?
- Was the examination of the fetal spine completed?
- Is the fetal spine intact?
- Do I need additional imaging?
- Are there any other findings noted on imaging?
Last updated March 2025
Download the leaflet:
Normal Fetal Spine – Mid-trimester scan