Nuchal translucency (NT) is only one of the parameters used for predicting Down’s syndrome. NT is an ultrasound parameter that is useful if it is measured between the 10-14th weeks of gestation. During this time of gestation, the fetal lymphatic system is still not developed enough to evacuate fluid from the back of the neck. After the14th gestational week, the fetal lymphatic system becomes developed enough to remove the fluid even if there is Down’s syndrome so the test has no sense.

There are more parameters for predicting Down’s syndrome such as: alpha-fetoprotein (AFP), unconjugated estriol (uE3), human chorionic gonadotropin (HCG), inhibin A and pregnancy-associated plasma protein A (PAPP-A). All these parameters are measured in the mother’s blood. A mother’s age and the age of the pregnancy are also very important parameters in detecting and predicting Down syndrome.

It is important to know that even the best combination of ultrasound findings and other blood parameters are only predictive and not diagnostic. For a true diagnosis, the chromosomes of the fetus must be examined. That can be achieved by performing an amniocentesis. However, amniocentesis brings with it the risk for miscarriage (1%) so it should be performed only if the risk for Down’s syndrome (according to the previous parameters) is 1 to 250 or larger.