When will I get scanned in pregnancy? What can the scans see?

Pregnancy scans: when they happen and what they show?

5 things to know about routine scans in pregnancy:

1. Ultrasound scans use sound waves to produce a black and white image. They are well known to be safe
2. All pregnant women in the UK are offered 2 routine scans during pregnancy. 
3. The first scan is the dating scan, and this is also part of Down’s screening if you opted to have this test. This scan is done at 11-14 weeks.  The sex of the baby cannot be seen on this scan (only rarely and its best not to rely on this).
4. The second scan is the anomaly scan which is between 18 and 20 weeks. This takes longer and looks at the baby top to toe in more detail. It also checks where the placenta is lying. This can usually see the baby’s sex and this is correct 90% of the time. Some babies do not want to reveal their secrets.
5. Whilst it is very reassuring to get a normal scan result, this is not a guarantee of a healthy baby. This is because many disorders are not visible on ultrasound scan. 

What do ultrasound scans do?

Ultrasound scans are used to screen your baby during pregnancy. If you are not at increased risk of complications, you will typically have two ultrasound scans on the NHS during pregnancy. Ultrasounds use sound waves to create a black and white image on a screen. They are known to be safe in pregnancy.

When will I get scanned and what will happen?

The first scan will occur around the end of your first trimester, usually between 11 and 14 weeks. This scan will check that there is only one baby in there, check that the heart is beating and also measure the size of the baby from the top of the head to the bottom.  This measurement is known as the ‘Crown-rump length’ or CRL for short. This measurement is used to date the pregnancy and calculate exactly how many weeks long the pregnancy is and also estimate a date of delivery. This is a more accurate way of dating a pregnancy than relying on pregnancy dates alone. Make sure you go to this scan with a full bladder as this makes the baby easier to see on the scan. If your bladder is not full, you may be asking to drink water until your bladder fills up before the scan is attempted.

If you decided that you wanted the baby to be screened for Down’s syndrome, then the sonographer will measure a tiny layer of fluid on the back of the baby’s neck at this scan. This measurement is known as the nuchal translucency measurement and is used in the calculation for risk in this test. This should measure less than 3.5mm. The sonographer will also look at the baby from top to toe. The baby is too small to make most diagnoses, but it is possible to get a good general view of the baby and check that everything is looking as it should for this stage in pregnancy.

You can ask for a picture of the baby at this scan but most hospital charge to provide this printed picture. Some hospitals may allow you to take a photo of the scan with your phone. It is usually too early to see the sex of the baby at this stage and any attempt to sex a baby on scan at this stage can be inaccurate, so do not rely on it!

What is scan no. 2 like?

If everything looks fine with this scan, then the next scan you will be offered is the anomaly scan, which occurs at around 20 weeks (between 18+0 and 20+6 weeks).  It is less important to go to this scan with a full bladder. This is a really detailed look at all of the baby’s organs from top to toe, aiming to diagnose 11 serious conditions in the baby. There are specific views of the baby that the sonographer has to obtain and store images of. Sometimes, other conditions or abnormalities in the baby can also be seen on this scan. The size of the baby will also be measured, and the site of the placenta will be checked. If you have a higher risk of placental complications during pregnancy, such as pre-eclampsia or growth restriction, then your will also have a measurement taken of your blood flow into the placenta. This is called a uterine artery Doppler, and gives an indication of how well the placenta has developed. This is the only part of the scan that will contain colour. However, this is just an artificial colour generated by the scan machine to tell which direction the blood is flowing in.

The 20 week scan usually takes around 20-30 minutes but can take longer if the baby is in a difficult position. If the scan takes longer, it does not mean there is a problem, it just means that the scan is difficult, possibly due to poor views due to a raised BMI or the baby lying in a difficult position. If a sonographer is worried about an image, sometimes they ask a colleague to come in and check an image. They will then tell you if there is a problem and arrange for you to have a further scan as soon as possible with a specialist doctor, known as a fetal medicine scan.

 If the sonographer cannot obtain all of the images needed, they may ask you to walk around for a short time before a re-scan is attempted, or they may ask you to reattend in 1-2 weeks. Again, if this happens it does not mean a problem, it is just, most likely, awkward baby!

This scan may see the baby’s sex – however be aware that this can occasionally be inaccurate. It is correct about 90% of the time and sometimes the baby does not want to reveal its secrets. If this happens, you will just have to wait as the NHS will not re-scan just for this reason. Errors with sexing a baby are more common when a girl is diagnosed on scan – in other words if you are told the baby is a girl, an error is more likely than if you are told the baby is a boy. This is for obvious reasons as male genitalia is clearer on scan! The NHS does not offer 3-D scans routinely.

It is important to be aware that even if the scan does not diagnose any concerns, this does not guarantee a healthy baby. This is because there are more potential problems that a baby can have than are possible to diagnose on a scan. Some problems are just not visible on scan, and some develop later on during the pregnancy. Even detection rates of the 11 disorders that the scan aims to diagnose are not 100%. It is, however, reassuring if the scan appears to be normal. As with the earlier scan, memento images are usually available for a small fee at most hospitals, and some hospitals will allow a still image to be taken using your phone camera. Most hospitals will not allow video to be records, although this does vary.