Fetal Anomaly Scan at 20 weeks
This scan is also known as a detailed anatomy scan.
The purpose of this scan is to check your baby is normal. Most babies are healthy, but unfortunately some have problems that cannot be predicted by a family history, or the health of the mother. Some of these problems can be serious.
When you attend for this scan we will assume that you wish to know about allproblems that are detected and any concerns that are raised. If you really do not wish to know if the baby has an abnormality, it may be best to decide not to have this scan.
Each part of the baby's body is examined. We check the development of the following organs or movements on the anatomy scan: head, brain, face, spine, arms, hands, fingers, heart, lungs, bowels, kidneys, bladder, legs, feet, the fluid around the baby, the umbilical cord and position of the placenta. If any abnormalities are detected then we will discuss the significance of the findings.
The majority all serious congenital malformations can be detected by the 20 week scan. So, if the baby appears normal on scan there is only a small chance that your baby will have a problem. This small chance is because some problems may not be present at 20 weeks but develop later in the pregnancy e.g. diaphragmatic hernias where there is a small hole in the muscle that separates the chest from the tummy (abdomen).
The scan is performed by a specialist sonographer or doctor and the whole examination is recorded. The scan is performed through the tummy wall. Occasionally we may need to perform the scan through the vagina if the baby's head is low in your tummy in order to check the developing brain.
The ability to accurately check the baby's development depends on several factors. The bodyweight of the mother and the how in which the baby is lying in the womb are important. As with all scans it is sometimes not possible to obtain what we consider perfect views of a certain part of the baby's body. In this case you willbe invited back for a repeat scan. This happens in about 1 out of 10 cases. Please do not be concerned if this happens.
We have access to a full counselling service for you should any problems be detected and we will send a copy of our report to your hospital, doctor or midwife to ensure good communication between all parties. This is because if we identify some problems on the scan such as a low placenta, you will need a repeat scan again later in the pregnancy to check that it has moved out away from the neck of the womb.
It is possible to determine the sex of the baby on scanning at 20 weeks but we will only tell you if you (and those with you in the scanning room) wish to know this information. If the scan does indicate the sex of the baby then this is right in 95% of cases.
We have included a list of some of the problems that can be detected by this type of ultrasound scan, along with likelihood of detection. (This comes from the RCOG website)
Problem |
What the problem is |
Chance of being seen |
Spina bifida |
Open spinal cord |
90% |
Anencephaly |
Absence of the top of the head |
99% |
Hydrocephalus |
*Excess fluid within the brain |
60% |
Major congenital heart problems |
|
25% |
Diaphragmatic hernia |
A defect in the muscle which separates the chest and abdomen |
60% |
Exomphalos/gastroschisis |
Defects of the abdominal wall |
90% |
Major kidney problems |
Missing or abnormal kidneys |
85% |
Major limb abnormalities |
Missing bones or very short limbs |
90% |
Cerebral palsy |
Spasticity |
Never seen |
Autism |
|
Never seen |
Down syndrome |
May be associated with heart and bowel problems |
About 40% |
* Many cases present late in pregnancy or even after birth |
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