Next scan. What you can expect during this scan.

At 11 weeks, your next scan is likely the NT (nuchal translucency) screening – a routine ultrasound. Foetuses with increased fluid at the base of their necks — a spot known as the nuchal fold — may have an extra chromosome. This fluid can be measured with ultrasound when the base of the neck is still transparent. Because the nuchal fold becomes less transparent as your baby grows, timing is crucial. In addition to Down syndrome, NT screens for congenital heart defects and other genetic disorders.

If your screening test shows that your baby may be at an increased risk for having a chromosomal defect, follow up tests may be offered.

The results of an NT screen can also be combined with a second trimester blood test called the quad screen, which provides a risk assessment using four entirely different markers present in the maternal bloodstream.

The nuchal translucency and the associated blood work don’t directly test for chromosomal problems, nor do they diagnose a specific condition. Rather, the results merely provide you with your baby’s statistical likelihood of having a problem. An abnormal result on the nuchal translucency or combined screening test doesn’t mean that your baby has a chromosomal problem, just that he or she has an increased risk of having one. In fact, most women who have an abnormal result on their screening test go on to have a perfectly normal and healthy child. At the same time, a normal result is not a guarantee that your baby is normal, but it does mean that it’s very unlikely your baby a chromosomal defect.

The first-trimester combined screening can detect approximately 80 percent of Down syndrome and 80 percent of trisomy 18 problems.

RISKS

Both the ultrasound and the accompanying blood tests are painless. The biggest problem might be the anxiety they can provoke. False positives are common (as are false negatives), which may lead to follow-up procedures that present greater risk. But try to keep it in perspective: The odds of having a completely healthy baby are overwhelmingly in your favour.

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