The anomaly scan

How does it work?

The anomaly scan takes place between 18 and 22 weeks of your pregnancy and is a detailed scan to check your baby is developing as he should. You’ll lie on a hospital bed and have jelly rubbed into your lower tummy, then the transducer will be passed over the area in different directions. The scan transmits high-quality sound waves through your uterus which bounce off your baby and are converted into an image.

The biggest echoes are from hard tissues, such as bones, which appear white on the screen. Soft tissues appear grey-flecked. Fluid does not return sound so spaces such as the stomach, bladder, blood vessels and amniotic fluid appear black. Seeing your baby on the screen is a very exciting, emotional experience. You’ll probably be allowed to take home photos and can usually find out the sex of your baby if you want to.

What are they looking for?

- Head, spine and abdomen

The shape and internal structure of the baby’s head will be examined for any problems and the sonographer will check the baby’s face for signs of a cleft palate. The spine is examined to make sure the vertebrae are all aligned and that the skin totally covers the spine. The baby’s abdominal wall is checked to ensure it covers all the internal organs at the front.

- Placenta
The placenta could be at the back or front of the womb and may be described as ‘fundal’, which simply means it’s near the top of your uterus. If the placenta is low it will be reaching towards the neck or bottom of the womb (cervix) and you will be asked to come in for another scan in the last trimester. If the placenta hasn’t moved into the fundal position, you may need to plan a caesarean delivery.

- Umbilical cord and amniotic fluid

The sonographer will look for three blood vessels in the umbilical cord and check there is enough amniotic fluid to allow your baby to move around freely.

- Heart

The size and shape of the heart will be examined along with the proportions of the four chambers. The sonographer will make sure the valves that control blood flow through the heart open and close with every heartbeat. Some hospitals offer a more detailed look at the heart, but this will depend on available equipment.

What if something’s wrong?

Half the major abnormalities that can affect a newborn are visible on this scan. Serious problems they are looking for include head structure, defects of the abdominal wall, major limb abnormalities, spina bifida, Down’s syndrome, kidney problems, a hole in the muscle separating the chest and abdomen, excess fluid in the brain and heart problems. Your baby will probably get the all clear, but remember there is still a small chance there could be a problem.

Your sonographer may talk about ultrasound markers – or ‘soft markers’. These are slight deviations from the normal baby anatomy, which may or may not indicate a problem. In themselves they are not considered an abnormality and most will disappear within weeks; however they may be a sign of an underlying chromosomal abnormality and need further investigation.

If a suspected or confirmed problem is picked up on the scan, you will be told immediately and another scan will be arranged with a specialist within 72 hours. Around 15% of scans need to be repeated but most of these are not associated with serious problems. Whatever the outcome, you will be supported by a team of midwives, obstetricians, paediatricians and physiotherapists.