What Can You See on a Nuchal Translucency Ultrasound?

There are many screening tools for pregnant women today. Most congenital abnormalities can now be detected before birth. Ultrasound is a commonly used tool to help diagnose fetal abnormalities in conjunction with other more invasive procedures. At 11 weeks a nuchal translucency ultrasound can be performed if any heart abnormalities or trisomy conditions are suspected.

Definition of Trisomy

A trisomy is a third chromosome in a pair. Instead of two chromosomes, there is one extra. Common disorders are Trisomy 21, Trisomy 18, and Trisomy 13. Trisomy 18 and 13 are lethal. Trisomy 21 is commonly referred to as Down 's syndrome.

Screening

All women are offered a screening for these disorders as part of their routing obstetric care. A blood test is performed to find markers for these abnormalities, and then more in-depth procedures can be performed.

Ultrasound

If a fetus is suspected of having a birth defect, or the mother is of advanced age, an ultrasound can be performed between 11 and 14 weeks. The ultrasound is used to measure the nuchal fold. This is the skin on the back of the neck at the base of the skull. The skin is very translucent at this gestational age, so fluid can be seen between the skin layers. On the ultrasound the skin appears as two bright white lines. The fluid is black and there should be a very small amount. If the nuchal fold is thicker than normal, which is greater than 2.5 mm, then one of the Trisomy disorders is suspected.

Amniocentesis

An amniocentesis can be performed if other tests show probable cause. This is where a small amount of amniotic fluid id drained with a syringe and sent to a lab for processing.

Chorionic Villus Sampling

This procedure yields the same results that an amniocentesis would, but can be done very early. An amniocentesis can't be performed until at least 16 weeks, but a CVS can be done at 11 weeks. This is appealing to anxious parents.

References

• What to Expect
• Baby Center