The anomaly scan at around 20 weeks

Week 20 – The Anomaly Scan

By now you are in the second trimester of your pregnancy and getting ready for your anomaly scan (or mid-pregnancy scan). This takes place around week 20 of your pregnancy and gives you a clear and close look at your baby. The anomaly scan is an important check of the development of your baby, the position of the placenta and health of your womb. It is a detailed scan and, in some cases, specific physical or chromosomal abnormalities may be found, including spina bifida and cleft lip. The anomaly scan is likely to be a time of nerves and excitement during your pregnancy, so you may wish to take along your partner, friend or an adult family member for support and to share the experience.

Having the scan and making a choice

If you live in the UK, the NHS will offer you an anomaly scan as part of your routine pregnancy care. There are no known risks to you, or your baby, in having the scan, but it is your choice whether you wish to go ahead. It is important to know what is involved and the information that you will be given during the scan. Your midwife will discuss this with you and give you written information to help you decide what you would like to do.

If you would prefer to have a separate 3-D or colour screening scan, you will need to contact a private clinic that provides this service to make and pay for your own appointment.

What to expect at the anomaly scan

The anomaly scan is carried out by a sonographer, at an appointed time, in a hospital or antenatal unit between week 18 and week 20 of your pregnancy. The scan will take place in a private room, in low light so that the sonographer will be able to see your baby clearly on a monitor. You will be asked to lie on a bed and expose your tummy. A clear gel will be applied and an ultrasound device will then be moved over your skin. From this, you will be able to view 2-D, black and white images of your baby on a nearby screen. The scan does not hurt but the sonographer may need to apply gentle pressure to get a good view of the baby.

The whole process usually takes about 20 to 30 minutes. In order to concentrate, the sonographer is likely to remain quiet during the scan and the results will be shared with you once the checks are complete. When you have discussed the scan’s findings, and are satisfied that you have all the information you need, you may wish to buy a photo of the scanned image of your baby. Don’t forget to ask the sonographer for this before you leave.

Sharing the results of the scan

In the majority of cases, the results of the 20 week anomaly scan will reveal a normal, developing baby and a healthy pregnancy. The scan will show that the baby’s bones, heart, brain, spinal cord, face, kidneys and abdomen have all developed well and are normal. You may be able to find out the gender of your baby, but, be aware, not all hospitals will provide this information. Check with your hospital on their policy.

In some cases the anomaly scan may identify a problem with your baby’s development. A second opinion from another member of staff may be sought and you could be offered additional follow up tests. This will undoubtedly be a difficult time as you consider and decide whether you want to proceed with further investigations. There will be support in place to help you with this.

Abnormalities detected during the 20 week scan

There are 11 specific conditions that the anomaly scan can potentially identify (NHS FASP predicted detection rates in brackets) :

• Anencephaly – abnormal development of the brain and skull (98%)
• Open spina bifida – a gap in the spine structure, leaving the spinal cord and nervous system vulnerable to infection or damage (90%)
• Cleft lip – malformation of the upper lip and sometimes the roof of the mouth (75%)
• Diaphragmatic hernia – a hole in the diaphragm which affects lung development (60%)
• Gastroschisis – a congenital defect where the intestines form on the outside of the baby (98%)
• Exomphalos – a weakness where the umbilical cord meets the abdomen (80%)
• Serious cardiac abnormalities – affecting either the structure or function of the heart (50%)
• Bilateral renal agenesis – absence of both kidneys (84%)
• Lethal skeletal dysplasia – a fatal abnormality affecting growth of bones in the chest, arms and legs (60%)
• Edwards’ syndrome (T18) – rare genetic defect causing severe physical and mental impairment (95%)*
• Patau’s syndrome (T13) – rare genetic disorder causing brain heart and other physical abnormalities (95%)*

Several of these conditions are incredibly rare, however, the sonographer is trained to identify them. Not all developmental problems can be detected at this stage, notably some heart defects and bowel obstructions.

Spina Bifida is one of the conditions that should be seen very clearly on a scan. A baby with spina bifida has a developmental defect in the spinal cord which will need surgery soon after birth. If your scan reveals the condition, a specialist team will discuss the associated problems and treatment, as well as, potentially, ending the pregnancy if you so wish.

A baby with a cleft lip also has a high chance of being detected at this 20 week scan. Surgery is likely to be needed for your baby when it is born and further treatment as your child continues to grow.

For a very small number of cases, the scan will show that your baby does not have fully developed internal organs, bones or brain tissue. Sadly, in these instances, no treatment is possible and you will be made aware and supported in the knowledge that the baby may die during the pregnancy or soon after birth.

Scanning the health of your womb

The scan will also take a look at the placenta, the umbilical cord and the amniotic fluid in your womb. In most cases, the placenta is positioned so that it won’t cause complications at the birth. However, if your placenta is low or covers the neck of your uterus you may need a further scan during the third trimester of your pregnancy to check that it has moved.

Being informed

In the vast majority of cases the anomaly scan will be uncomplicated and you will continue to have a normal and healthy pregnancy. However, it is always best to be informed and prepared ahead of your week 20 scan and to have discussed any concerns with your midwife or doctor beforehand.

* Detection rates under review