What is an anomaly scan?
An anomaly scan takes a close look at your baby and your uterus (womb). The person carrying out the scan, called the sonographer, will check that your baby is developing normally and look at where the placenta is lying in your uterus.
You will be offered the scan, which is sometimes called your mid-pregnancy ultrasound scan, when you are between 18 weeks pregnant and 20 weeks plus six days pregnant.
Baby at 20 weeksSeeing your baby on a screen is a wonderful event. The image, right, shows a babys face and hands at 20 weeks, and gives you an idea of what you will be able to see at this scan.
Your loved ones will be welcomed by most hospitals to share the experience with you.
You may want to know the sex of your baby and to have a photo. However, although its lovely to see your baby, the scans main purpose is to confirm that your baby is developing normally.
Do I have to have an anomaly scan?
Its up to you. Early in your pregnancy your midwife should give you written information about why the scan is being done, how it will help and what it wont be able to tell you. This will allow you time to decide whether you would like the scan.
What will I be able to see?
Most hospitals allow you to watch the scan, which takes about 20 minutes, as it is being performed. If you havent already had a scan in this pregnancy, the sonographer will check that there is only one baby, and confirm your due date.
The sonographer will point out your babys heartbeat and parts of his body, such as his face and hands, before looking at him in detail.
It may be hard for you to make out your babys organs, because the sonographer will look at them in cross section.
Your babys bones will appear white on the scan and his soft tissues look grey and speckled. The amniotic fluid surrounding your baby will look black.
After showing you your baby on the screen, some sonographers will turn the screen away for the rest of the scan and show you views at the end. Some hospitals have a second monitor at the foot of the couch so that you can watch the entire scan.
By 20 weeks, its often possible for you to find out whether your baby is a boy or a girl, but not all hospitals will tell you. If you want to know, ask your midwife about your hospitals policy.
Can I have a photo?
Most hospitals will allow you to purchase a picture of your baby. These will probably be printed on thermal paper which is heat sensitive, so dont laminate them. If you want copies, its best to scan them into a computer or photocopy them.
What will the sonographer look at?
The sonographer will examine all your babys organs and take measurements. She will look at:
The shape and structure of your babys head. At this stage severe brain problems, which happen very rarely, are visible.
Your babys face to check for a cleft lip. Cleft palates inside a babys mouth are hard to see and are not often picked up.
Your babys spine, both along its length and in cross section, to make sure that all the bones align and that the skin covers the spine at the back.
Your babys abdominal wall, to make sure it covers all the internal organs at the front.
Your babys heart. The top two chambers (atria) and the bottom two chambers (ventricles) should be equal in size. The valves should open and close with each heartbeat.
Your babys stomach. Your baby swallows some of the amniotic fluid that he lies in, which is seen in his stomach as a black bubble.
Your babys kidneys. The sonographer will check that your baby has two kidneys, and that urine flows freely into his bladder. If your babys bladder is empty, it should fill up during the scan and be easy to see. Your baby has been doing a wee every half an hour or so for some months now!
Your babys arms, legs, hands and feet. The sonographer will look at your babys fingers and toes, but not count them.
As well as this detailed look at how your baby is growing, the sonographer will check the placenta, the umbilical cord and the amniotic fluid.
The placenta may be on the front wall (anterior) or the back wall of your uterus (posterior), usually near the top (or fundus). If the placenta is near the top, it may be described as fundal on your scan notes.
The placenta will be described as low if it reaches down to or covers the neck of your uterus (your cervix). If the placenta is lying low in your uterus, youll have another scan in the third trimester to check its position. By then, its likely the placenta will have moved away from your cervix.
It is possible to count the three blood vessels (two arteries and a single vein) in the umbilical cord, but your sonographer may not do this. Its not routine procedure. She will check to see thats theres enough amniotic fluid for your baby to move freely, though.
During the scan, the sonographer will measure parts of your babys body, to see how well he is growing. The sonographer will measure your babys:
head circumference (HC)
abdominal circumference (AC)
femur or thigh bone (FL)
The measurements should match up to whats expected for your baby, given his anticipated due date. The due date will have been established at your dating scan. If your anomaly scan is the first scan youve had, it will be used to establish a due date.
Which abnormalities can be seen on the scan?
Sonographers have a list of conditions to look out for. The conditions are on the list either because they are very serious and may even mean a baby cant survive, or because they are treatable after birth.
If the conditions are treatable, it will help the hospital team to know in advance. The team can then make sure your baby has the right care as soon as hes born.
Some conditions are easier to spot than others; some are hard to see at all. Most of the conditions on the list are very rare. Heres the list of conditions, and the percentage chance of your sonographer seeing each one, if your baby has it:
Absence of the top of the head (anencephaly): 98 per cent
Cleft lip: 75 per cent
Defect of the abdominal wall (exomphalos): 80 per cent
Defect of the abdominal wall (gastroschisis): 98 per cent
Missing or very short limbs: 90 per cent
Defect of the spinal cord (spina bifida): 90 per cent
Major kidney problems (missing or abnormal kidneys): 84 per cent
Hole in the muscle separating chest and abdomen (diaphragmatic hernia): 60 per cent
Excess fluid within the brain (hydrocephalus): 60 per cent
Edwards syndrome or Pataus syndrome (chromosomal abnormalities): 95 per cent
Major heart problems (defects of chambers, valves or vessels): 50 per cent
Some conditions, including heart defects and bowel obstructions, may not be seen until later in your pregnancy. Having your anomoly scan will most likely rule out all these conditions, as the vast majority of babies are born healthy.
What if there are signs of a problem?
Most problems that need repeat scanning are not serious. About 15 per cent of scans will be done again for one reason or another.
The most common reason is that the sonographer has not seen everything she needs to see. This may be because your baby is not lying in a good position, or you are overweight, in which case the scan should be repeated at 23 weeks.
If your sonographer finds or suspects a problem, you will be told straight away. You should have an appointment for a scan with a fetal medicine specialist within 72 hours.
If doctors suspect that your baby has a heart problem, you will be asked to come in a fetal echo scan. The fetal echo scan will take a detailed look at your babys heart.
If any scan reveals a serious problem, you should be given plenty of support to guide you through all the options. Although such serious problems are rare, some families are faced with the most difficult decision of all, whether to end the pregnancy.
Other problems may mean a baby needs surgery or treatment after birth, or even surgery while he is still in the uterus. There will be a whole range of people to support you through any difficult times, including midwives, obstetricians, paediatricians, physiotherapists and the hospital chaplain.