All women will be offered at least 2 scans in pregnancy - and some women will be offered additional scans too.
This guide will explain the different scans that are offered in pregnancy, and what the sonographers are looking at when you go for your scan.
What is an ultrasound scan?
An ultrasound scan uses high-frequency sound waves to create images of your baby inside your uterus. It allows the sonographer to assess your baby's growth, development and well-being throughout pregnancy.
Unlike x-rays, ultrasound does not use radiation, and therefore it is considered safe to use in pregnancy.
Although ultrasound scans can provide valuable information about your baby's development, it is important to note that they cannot detect every condition or abnormality.
The Dating Scan
Typically, your first scan in pregnancy is your 'dating scan'. The purpose of this scan is to:
- Estimate how many weeks pregnant you are and to calculate your due date (your due date is when you are 40 weeks pregnant). This is based on measurements of your baby
- Confirm that the pregnancy is in your uterus, and that baby has a heartbeat
- Detect how many babies are present (a singleton, twins, triplets or so on)
For women who have chosen to have the screening for Down's, Edwards and Patau's syndromes, this scan will also look for markers to help determine whether baby is affected by one of these chromosomal abnormalities.
The dating scan is carried out between 10 and 13+6 weeks of pregnancy.
The Anomaly Scan
The anomaly scan is an opportunity for the sonographer to have a detailed look at your baby's anatomy and the surrounding structures.
For example, the sonographer will be able to study:
- Your baby's brain, spine, heart, stomach, kidneys, limbs and other major organs
- The growth of your baby
- The amniotic fluid volume, the placental location (to ensure that the placenta is not located close to your cervix), as well as the number of cord vessels (3 is normal, but occasionally babies can have a 2 vessel cord)
The anomaly scan also looks for 11 rare but serious physical and chromosomal conditions in your baby:
- Anencephaly (underdevelopment of the brain and skull)
- Spina bifida (where the spinal cord does not close properly)
- Cleft lip (an opening in the upper lip that may extend to the palate)
- Diaphragmatic hernia (a hole in the diaphragm allowing abdominal organs to move up into the chest)
- Gastroschisis (an abdominal wall defect where organs develop outside of the body)
- Exomphalos (an abdominal wall defect where organs develop outside of the abdomen inside a sac)
- Serious cardiac abnormalities (structural defects of the heart)
- Bilateral renal agenesis (where the kidneys do not develop properly)
- Lethal skeletal dysplasia (severe abnormalities in bone growth and development)
- Edwards syndrome, T18 (a genetic condition causing severe physical disabilities and developmental delays)
- Patau's syndrome, T13 (a genetic condition linked to severe physical and intellectual disabilities)
Although this list sounds alarming, it is important to remember that these conditions are extremely rare. If the sonographer does find anything concerning at the anomaly scan, you will be referred to a specialist for further diagnostic tests, if you wish to have them.
The anomaly scan is also when the sonographer can tell you whether you are expecting a girl or a boy. It is your choice whether you find out this information - some parents are keen to know, others choose to wait until baby is born to discover whether they have a girl or a boy.
The anomaly scan is carried out between 18 and 20+6 weeks of pregnancy.
The Presentation Scan
Some (but not all) hospitals offer a presentation scan at around 36 weeks of pregnancy. This is to determine whether baby is head down ('cephalic') as is optimal, or bottom down ('breech').
If baby is found to be breech, you may be offered a procedure called an 'external cephalic version' in which your doctor tries to turn baby into the head down position (also called the cephalic presentation).
Additional scans
There are lots of reasons why women might be offered additional scans in pregnancy. Common reasons for additional scans in pregnancy include:
- If there are certain medical conditions in the mother (such as diabetes or high blood pressure)
- If there are certain concerns about baby, such as their growth, or reduced movements
- If you are expecting twins, triplets or other multiple pregnancies
- If you experienced complications in a previous pregnancy or birth
Scans do provide lots of information about baby's growth and development. However, they are not perfect and they cannot detect every condition or abnormality. The accuracy of the scan can depend on a number of factors including what is being assessed, the stage of your pregnancy, your baby's position and the experience of the sonographer.
Towards the end of pregnancy, estimated fetal weight on scan can differ from your baby's actual birth weight by around 10 to 15%.
Having additional scans in pregnancy doesn't necessarily mean that anything is wrong - often it is just a way of monitoring your pregnancy more closely.
What happens during a scan?
When you come for a scan in pregnancy, you will be in a private room and will be helped to lie on a couch. Jelly is applied to your abdomen, and the sonographer will move a handheld probe over your tummy.
Sometimes you may be asked to change your position so that the sonographer can get a better view of baby. Sometimes a transvaginal scan is recommended - this involves a probe being inserted into your vagina and it can allow the sonographer a better view of baby.
Appointments usually last about 20 minutes, but may take longer depending on baby's position and so on.
... top tip
If your hospital allows it, consider bringing your partner, birth partner or another person who can support you. It is normal to feel nervous before a scan, and having someone with you can make the experience more reassuring.
A note from the labour ward
When a woman comes to labour ward, one of the things I review as her midwife is the scans that she has had in pregnancy. These provide me with lots of information including where the placenta is, whether there were any concerns about baby's growth, and whether there are any findings that could potentially influence her care in labour.