A Milestone in Pregnancy – The Anomaly Scan


What Is An Anomaly Scan?

The anomaly scan is a detailed anatomy ultrasound scan of the baby in the womb, performed usually between 18 and 21 weeks of pregnancy, which takes a very close look at baby, all its organs in a systematic way, assessing growth and overall health and wellbeing of the baby. It is also performed for twin and other multiple pregnancies. The ultrasound is done trans-abdominally, which means the probe is placed and moved over the surface of the mother’s abdomen. The Sonographer can then transfer the images live to a monitor, which you can watch throughout the scanning process.

Is the Timing of the Scan Important?

Yes, because between 18 and 21 weeks, the baby is more fully formed, with details of the various organs and bone structures clearly visible. If the scan were to be performed earlier, some of the structures will not have matured enough to be accurately assessed e.g. the heart. As your baby grows beyond 21 weeks, it becomes harder to view all of the organs as baby might not be as free moving and limb and positions may obscure the view to important organ structures, making it difficult to measure and ensure all is well.

What Will the Anomaly Scan Tell Me About My Baby?

We can gain a host of vital information from this milestone scan in pregnancy, from the position of the placenta, amount of fluid around the baby, the blood flow and the all-important look at the organs, including the brain, heart, lungs, liver, stomach, kidneys, palate and of course the baby’s limbs and digits. The first thing will be to see the heart beat and watch as the baby moves in the womb. These are the most reassuring checks and includes baby’s current position, i.e. head down, transverse lie, (across) or breech (head up). The scan will determine the position of the placenta, which is important for labour. The placenta does move during pregnancy so even if it is low lying, it may move out of the way later in the pregnancy.

What are the Details?

An in-depth measurement protocol is used including three types of head measurements and a critical measurement of the space at the back of the brain which contains cerebral-spinal fluid, which is important in normal brain function. This is noted on the scan as the Cisterna Magna. Next the Sonographer will view and measure the chambers of the baby’s heart, followed by the abdomen and finally the limbs. These critical measurements will be recorded on your Anomaly Scan report. It should also be possible to find out the gender of your baby, dependant on the position at the time of the scan and your preference to know.

The anatomy of the baby or babies will also be visualised and this will include a comprehensive view of the head, brain, face, spine, chest, chambers of the heart and blood flow, abdominal wall, intestinal tract, kidneys, bladder, limbs and the skeleton. All of this information is critical in determining the normality of the baby and predicted health at birth. The measurements are useful in determining that the baby’s growth is in line with what is normal at this stage in pregnancy.

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The contents on this site is for information only, and is not meant to substitute the advice of your own physician or other medical professional.