Ultrasound scans

Ultrasounds can pick up a variety of problems: The purpose of the anomaly scan at 18-20 weeks is to reassure the mother that her baby doesn't appear to have any gross structural abnormalities. This isn't however a guarantee, as not all abnormalities will be detected by a scan at this time. Conditions that have a high rate of detection at the 18-20 week scan include:

• Anencephaly (where the brain has not developed)
• Hydrocephaly (where there is excessive fluid in the cavities of the brain)
• Spina Bifida (where the spine does not develop fully)
• The limbs and internal organs can be checked, as well as the face for cleft palate.

Some of the most common problems of newborn babies, like heart defects and abnormalities, together with abnormalities of the major blood vessels, can’t always be detected.

Remember that certain abnormalities may be identified which correct themselves by the time your baby is born. For example, an early scan could indicate an abnormal position of the placenta. If this is the case, a review will be arranged for a later date, when it’s often discovered that the placenta has ‘corrected’ itself.

What if the scan shows a problem?

You will, of course, be frightened and upset if a scan suggests a problem. If this happens, several more scans may be taken at intervals and compared and it may be that other tests are also needed to confirm a detected abnormality.

About half of the major abnormalities will be seen on a scan and half will not. Some types of congenital abnormality are more likely to be detected than others:

• Anencephaly – absence of brain – has a 99% chance of being seen
• Spina Bifida – open spinal cord – has a 90% chance of being seen
• Hydrocephalus – excess fluid within the brain – has a 60 % of being seen
• Major defects of the abdominal wall have a 90% chance of being seen
• Major limb abnormalities have a 90% chance of being seen
• Major kidney problems have an 85% chance of being seen
• Down’s syndrome has a 40% chance of being seen
• Major congenital heart problems have a 25% chance of being seen
• Cerebral Palsy and autism are NEVER SEEN

If the scan predicts the sex of your baby it is usually 95% correct.

The value of identifying an abnormality at an early stage is that it offers parents options. Some couples – probably the majority for serious lesions – will elect to terminate the pregnancy. Couples who choose to continue the pregnancy have the opportunity to prepare themselves, through discussions with health care personnel and self-help groups, while medical staff can ensure the appropriate care during pregnancy and after delivery.

Are scans safe?

Medical researchers are continuing to monitor for possible long-term effects of ultrasound on the hearing of children and babies exposed to ultrasound in the womb, but ultrasound examinations have been in use in pregnancy for nearly 50 years, and to date, no side effects have been detected.

Reports of ill-effects such as low birthweight, speech and hearing problems and brain damage, have been investigated, but have not been confirmed in large controlled studies.

Random studies have suggested that at least one routine scan in pregnancy to confirm gestational age is valuable, but the final decision about whether or not to have the ultrasound scan is entirely yours. Certainly the benefits far outweigh any risks.