This ultrasound is often called a fetal morphology or anomaly scan. The scan takes a close look at your baby and your uterus (womb). The person carrying out the scan (sonographer) will check that your baby is developing normally, and she'll look at where the placenta is lying in your uterus.
This image shows a baby's face and hands at 20 weeks, and gives you an idea of what you will be able to see at this scan.
You'll be offered the scan at your booking appointment with your hospital or doctor, or your GP may offer to refer you for the ultrasound. The scan will happen when you're between 18 weeks and 20 weeks plus six days pregnant. Seeing your baby on a screen can be a really exciting event. You can also take your partner, a friend or a family member along to share the experience with you.
Bear in mind that the scan's main purpose is to check that your baby is developing normally, rather than whether you're expecting a boy or girl. Sometimes excess wind or having too much tummy fat obscures the view, so it's hard to tell a baby's gender accurately. And some hospitals or ultrasound centres have a policy of not telling parents-to-be, to prevent mistakes from happening. When you book in for your scan, ask about your centre's policy.
Do I have to have an anomaly scan?
It's up to you. Early in your pregnancy your doctor or midwife will explain why the scan is being offered, how it will help, and what it won't be able to tell you. This will allow you time to decide whether or not you would like the scan.
What will I be able to see on the scan?
Most ultrasound centres and hospitals allow you to watch the scan, which takes about 30 minutes, as it's being performed. If you haven't already had a scan in your pregnancy, the sonographer will check that there's only one baby, and confirm your due date.
The sonographer will point out your baby's 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 baby's organs, as the sonographer will look at them as a cross section.
Your baby's bones will appear white on the scan, and his soft tissue will look grey and speckled. The amniotic fluid surrounding your baby will look black.
After you've seen 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 centres have a second monitor at the foot of the couch, so you can watch the entire scan.
Can I have a photo of my scan?
Most hospitals and centres will offer printed photographs or a CD/DVD of images from your scan. They will often charge you for these so you may want to ask about your options when you make your booking. Some private ultrasound clinics now offer to upload images to an app that you can get free for your smart phone.
Make sure you tell your sonographer your wishes about knowing the baby's gender. If you don't want to know make sure you let the sonographer know to be discreet if it's obvious to her.
What will the sonographer look at on my scan?
The sonographer will examine all your baby's organs and take measurements.
She will look at:
- The shape and structure of your baby's head. At this stage, severe brain problems, which happen very rarely, are visible.
- Your baby's face, to check for a cleft lip. Cleft palates inside a baby's mouth are hard to see and aren't often picked up.
- Your baby's 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 baby's abdominal wall, to make sure it covers all the internal organs at the front, as well as check the placenta, umbilical cord and the amniotic fluid.
- Your baby's 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 sonographer will also examine the major veins and arteries that carry blood to and from your baby's heart.
- Your baby's stomach. Your baby swallows some of the amniotic fluid that he lies in, which is seen in his stomach as a black bubble.
- Your baby's kidneys. The sonographer will check that your baby has two kidneys, and that urine flows freely into his bladder. If your baby's 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 baby's arms, legs, hands and feet. The sonographer will look at your baby's fingers and toes, but not count them.
The placenta may be on the front wall (anterior) or the back wall (posterior) of your uterus, 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, you'll have another scan in the third trimester to check its position. By then, it's likely the placenta will have moved away from your cervix.
It's possible to count the three blood vessels (two arteries and a single vein) in the umbilical cord, but your sonographer may not do this. It's not routine procedure. She will check to see that's there's enough amniotic fluid for your baby to move freely, though.
During the scan, the sonographer will measure parts of your baby's body, to see how well he's growing.
The sonographer will measure your baby's:
- head circumference (HC)
- abdominal circumference (AC)
- thigh bone (femur) (FL)
The measurements should match up to what's expected for your baby, depending on when his due date is. The due date will have been established at your dating scan. If your anomaly scan is the first scan you've had, it'll 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 either very serious, which may mean that a baby can't survive, or they may be treatable conditions, once your baby is born.
If the condition is treatable, it will help the hospital team to know in advance, so they can make sure your baby has the right care as soon as he's born.
Some conditions are easier to spot than others, and some are hard to see at all. Most of the conditions on the list are very rare.
Here's 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, where the bowel and liver protrude (exomphalos): 80 per cent
- defect of the abdominal wall, where the intestines protrude (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 Patau syndrome (chromosomal abnormalities): 95 per cent
- major heart problems (defects of chambers, valves or vessels): 50 per cent
Having an anomaly scan will most likely rule out all these conditions, as the vast majority of babies are born healthy. Some conditions, though, including heart defects and bowel obstructions, may not be seen until later in your pregnancy.
What if there are signs of a problem on my scan?
Most problems that need repeat scanning aren't 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 that you're a bit overweight, in which case the scan should be repeated at 23 weeks.
If your sonographer finds or suspects a problem, you'll 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'll be asked to come in for a fetal echo scan. The fetal echo scan will take a detailed look at your baby's heart.
If any scan reveals a serious problem, you should be given plenty of support to guide you through all the options. Though serious problems are rare, some families are faced with the most difficult decision of all, whether to continue with the pregnancy.
Other problems may mean that your baby needs surgery or treatment after birth, or even surgery while he's still in your uterus (womb). There will be a whole range of people to support you through this, on the rare occasions where problems are detected.
