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20 week scan

Updated: Oct 2, 2021

The Anomaly scan is the scan to check crucial elements in your baby’s development. It is typically performed between 18-22 weeks of pregnancy. During the scan the sonographer will be looking for lots of different developmental markers; depending on their view (which can be restricted by baby lying in a difficult position, or by high maternal BMI) they should be able to make accurate assessments of your baby’s wellbeing.

What do they look for?

The sonographer wants to make sure your baby’s brain is developing normally, and baby is big enough for her to do this now. She looks at the shape and size of both the head and the brain. In 90% of cases, the scan can identify the condition, Anencephaly.

She or he will also check on your baby’s heart; they are looking to see all four chambers of the heart making sure they’re equal in size, and make sure that they are all functioning typically. She or he will also want to make sure they are pumping blood correctly, they will check this by looking at the arteries through colour doppler ultrasound- which will show in colour on the screen and will graph the direction and speed of the blood flow.

The sonographer will also want to look at baby’s spine to check its alignment, and for signs of the condition Spina Bifida- and they will be able to spot this around 90% of the time, too.

The Sonographer looks at baby’s other organs to look for abnormalities. This includes the kidneys, to check if there are two, and the bladder, to check urine is flowing freely from kidneys to the bladder.

Did you know; you can see baby having a wee, during an ultrasound?

They will also be looking at the stomach, making sure baby is swallowing correctly, as well as the abdominal wall, to check that your baby’s intestines, stomach and other internal organs are growing within it and being protected by it. Amazingly, an intestinal protrusion can be seen in 98% of scan where it is present. However, the condition is still rare.

He or she will want to look at baby’s placenta. By 20 weeks the placenta has almost settled into place, in most cases, this is either anterior (to the front) or posterior (to the back) and high, though occasionally the placenta is in a low lying position. This generally doesn’t cause issues unless the placenta is covering the cervix, in which case natural birth may not be possible. You are normally invited back for a further scan to double check the placenta has moved away from the cervix around 32-36 weeks. Generally, the placenta does move sufficiently as your stomach expands further.

They are also keen to look at the umbilical cord, where they will be looking for the two main arteries and the vein that make up the cord, again, they use colour doppler ultrasound to help them see this clearly.

Once they have finished looking at baby’s internal development they will look at baby’s face. They are checking for a cleft lip. This can be seen in around 75% of scans where baby has a cleft lip. A cleft lip itself is unlikely to be dangerous to baby and can be operated on soon after baby is born (should you decide to go ahead) and have the cleft closed.

However, a cleft lip can indicate a cleft palate, which can be a little trickier to operate on- but it is still possible to resolve. It is very unlikely for a sonographer to be able to see a cleft palate during the scan. Initial difficulties may include difficulty in feeding, ear infections and glue ear, possible dental problems and future difficulty with speech.

They will check on baby’s limbs, taking measurements and checking for typical development. They will look at baby’s fingers and toes, too, but don’t be surprised if they don’t tell you if your baby has ten of each- because it is a relatively minor issue that doesn’t impact on the health of your baby, many professionals agree that parents don’t always need to know- as it can cause undue stress or concern. They will often count them without you even realising.

Lastly, the sonographer will check the fluid surrounding baby (your amniotic fluid). She will measure the deepest and the shallowest pool and calculate an average. This is the fluid that enables baby to move freely and helps cushion them.

Along with detailed scanning of the baby’s organs and bones, the sonographer will take several measurements (baby’s head circumference, in your notes as HC, their femur length, in your notes as FL and their abdominal circumference, in your notes as AC). These measurements are converted into a gestation and then they can estimate your baby’s growth on a percentile chart. For instance, baby’s head may be measuring 20 weeks and 3 days, and on the 51st percentile, their legs may be the same, and their tummy might be measuring at 21 weeks and 2 days, putting it on the 79th percentile. Any size combinations can be completely normal, though if there are any suspected problems, your sonographer will discuss them with you on the day.

Is Everything Going to be OK?

In most cases; your baby will be given the all clear and you can purchase scan photos to take away with you, it may be the last time you see your baby before he or she is born, so try to enjoy the experience. If there are any issues, you will be offered the correct support, and remember, if you don’t understand anything- just ask!

Will I find out the gender?

In some cases, your sonographer may attempt to determine gender during this scan, however; the purpose of this ultrasound is to determine health above all else. Gender is of no real concern to the health trust and many hospitals will not tell you the gender during your ultrasound. If you have a known condition that only affects one gender, this should be noted on your records and the gender should be determined. It is worth asking if your hospital will check baby’s sex if you wish to find out, so you know if you need to book a private gender scan or not.

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