Your 20-Week Ultrasound Scan
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Markers for Down syndrome
Although ultrasound at this stage is not a reliable way to detect Down syndrome, it can pick up certain signs known as "soft markers" that may suggest that your baby has an increased risk of Down syndrome. However, many markers are very common and are not usually a cause for alarm unless you already have an increased risk for Down syndrome, for example, because you are over 35 years of age, or were given a high risk from a previous screening test. Common markers include a bright spot in your baby's heart, seen in about 1-2 percent of normal babies; extra fluid in your baby's kidneys; short leg or arm bones; thickened neck skin (nuchal fold); and bright (echogenic) fetal intestines.
Some specific abnormalities are linked with a far higher risk of Down syndrome or other chromosomal abnormalities. These include certain kinds of heart defects and other major malformations, such as abnormalities in the spleen.
What happens next
If the sonographer detects soft markers, he or she will discuss the findings and may suggest a diagnostic test, especially if you already have an increased risk of Down syndrome. However, an earlier all-clear from a diagnostic test means that you can be confident your baby's chromosomes are normal. If an obvious abnormality is seen, and you haven't had a diagnostic test, this will probably be strongly advised. Having information from the scan will help you decide whether you want to proceed with a test. Whatever your decision, any associated abnormalities will be monitored throughout your pregnancy.
Your baby's checkups
What the ultrasound looks at
During this scan, your baby's organs are examined in detail and therefore it can take a little longer to perform than previous scans. For most, the scan provides reassurance that their baby is developing normally. The following areas will be checked.
- The brain, including the fluid-filled spaces inside the brain and the shape of the back of your baby's brain (cerebellum).
- The spine, to check for spina bifida or other problems.
- The upper lip, to check for cleft lip.
- The heart, to rule out any major heart malformations. The heartbeat will be checked too.
- The stomach and diaphragm.
- The kidneys and bladder, making sure that both kidneys are present and there are no blockages or malformations.
- The abdominal wall, to look for a defect, known as gastroschisis.
- Your baby's limbs, to make sure there are no hand or feet malformations, such as club foot.
- The umbilical cord, to check that this has a normal number of blood vessels.
Excerpted from Pregnancy Day by Day.
Copyright © 2009 Dorling Kindersley Limited.
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