Nuchal Translucency Screening

What is Nuchal Translucency?

 Nuchal translucency (NT) is the sonographic appearance of a collection of fluid under the skin behind the fetal neck in the first-trimester of pregnancy.

Who Nuchal Translucency screening is for?

NT screening is available for any pregnant woman. However it can be especially helpful for;

->  Older moms-to-be (>40 years old)

-> Family history of Chromosomal abnormalities

-> Mother who may be hesitant about more invasive genetic testing, like CVS and amniocentesis, because of the increased risk of miscarriage associated with them.

How accurate this Nuchal Translucency screening is?

The accuracy of the test is, however, dependent on the;

->  Skill of the sonographer performing it

-> The sensitivity of the equipment

NT measurements are not conclusive, so the NT screening test can't tell you for sure whether your child has a chromosomal disorder, but it can be combined with other data as below to provide a statistic about the likelihood of such a disorder;

-> Older pregnant woman (>40 years old)

-> Family history of Chromosomal abnormalities

-> Blood tests - beta-hCG and pregnancy associated plasma protein A (PAPPA-A)

The results of these two blood tests plus the NT screening, known as the first trimester combined screening, can be combined into one number that represents the likelihood of having a child with a genetic abnormality. This information can be helpful to parents who are trying to decide whether to have more invasive genetic tests, such as amniocentesis or chorionic villus sampling (CVS).

How Nuchal Translucency screening is done?

This procedure is done during an ultrasound. The sonographer will first move the transducer across your belly to measure your baby from crown to rump to ensure that the fetal age is accurate. The fetal crown-rump length should be between 45 and 84mm. Then he or she will locate and measure the nuchal translucency (if you're lucky your baby will cooperate by moving into a position where the measurement will be optimum).

When Nuchal Translucency screening is done?

NT screening must be done between weeks 11 and 14. That is why an accurate date of conception is important for an accurate result. Before 11 weeks, the scan is difficult to be done because your baby is still so tiny. It would also be too early to combine it with your first trimester blood test. After 14 weeks, any excess fluid may be absorbed by your baby's developing lymphatic system. 

What is the normal measurement?

An NT of less than 3 mm is considered normal when your baby measures between 45mm and 84mm. The NT normally grows in proportion with your baby.

What abnormal result mean?

An increased NT (>3 mm) means there is a greater risk of chromosomal abnormalities or cardiac defect. However, it does not tell for certain that the baby has chromosomal abnormalities.

What should I do if I’m high risk?

The only way for certain if your baby has Down’s syndrome or other chromosomal abnormality is to have a diagnostic test such as CVS or amniocentesis.