Soft markers for chromosomal anomalies

By Dr Joe Kabyemela, MD

Most mothers in the developed world and increasingly in the developing countries will have what is termed as an anomaly scan offered around the mid-way stage of a pregnancy. This is meant to have a detailed look at the fetus for any possible structural abnormalities.

Chromosomal disorders such as Down’s syndrome are known to be associated with abnormalities and this detailed scan could be the first opportunity to identify the anomalies which could raise the alert that something may be wrong. Of-course an ultrasound scan is not conclusively diagnostic of such conditions. However, it may provide an opportunity to get a diagnosis before the baby is born.

Ultrasound soft markers in second trimester

This anomaly scan is typically done around 19-22 weeks gestation. When examining the major orga omphalocele ns and limbs, there are so-called soft markers that are looked for. These are classified as either major or minor. There are many of these and, quite frankly, if you exclude people with medical knowledge, some of the names and terms will not make sense to most people. Here are some of them:

Major structural markers:

Heart:

· Endocardial cushion defect,

· Ventricular septal defect (VSD) (hole in the heart),

· Hypoplastic left heart syndrome (underdeveloped left side of the heart),

· Tetralogy of Fallot (a combination of four specific heart defects found together)

Gastrointestinal tract (bowel)

· Esophageal and duodenal atresia (obstruction of the upper gastrointestinal tract),

· Small bowel obstruction,

· Diaphragmatic hernia

· Omphalocele (intestines outside the abdominal cavity) as shown on the pictures (right)

Central Nervous System (brain)

· Ventriculomegaly

· Holoprosencephaly (misshapen head)

· Microcephaly (abnormally small head)

· Dysgenesis of corpus callosum

· Abnormal posterior fossa, also known as Dandy-Walker complex

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Renal pelvis dilatation

Echogenic Bowel

The two pictures show an omphalocele where abdominal organs, mainly the intestines, but sometimes the liver, are outside the abdominal cavity. Surgical correction is always required. At least a quarter (25%) of all affected children will have other defects such as those of the heart or diaphragm. There is also an increased possibility of a chromosomal abnormality. Ultrasound scan images (top) are typical and mean the diagnosis is almost always made before the birth.