<P> How to define a normal or abnormal nuchal translucency measurement can be difficult . The use of a single millimeter cutoff ( such as 2.5 or 3.0 mm ) is inappropriate because nuchal translucency measurements normally increases with gestational age ( by approximately 15 % to 20 % per gestational week from 10 to 13 weeks ) . At 12 weeks of gestational age , an `` average '' nuchal thickness of 2.18 mm has been observed ; however , up to 13 % of chromosomally normal fetuses present with a nuchal translucency of greater than 2.5 mm . Thus for even greater accuracy of predicting risks , the outcome of the nuchal scan may be combined with the results of simultaneous maternal blood tests . In pregnancies affected by Down syndrome there is a tendency for the levels of human chorionic gonadotropin ( hCG ) to be increased and pregnancy - associated plasma protein A ( PAPP - A ) to be decreased . </P>
<P> How to define a normal or abnormal nuchal translucency measurement can be difficult . The use of a single millimeter cutoff ( such as 2.5 or 3.0 mm ) is inappropriate because nuchal translucency measurements normally increases with gestational age ( by approximately 15 % to 20 % per gestational week from 10 to 13 weeks ) . At 12 weeks of gestational age , an `` average '' nuchal thickness of 2.18 mm has been observed ; however , up to 13 % of chromosomally normal fetuses present with a nuchal translucency of greater than 2.5 mm . Thus for even greater accuracy of predicting risks , the outcome of the nuchal scan may be combined with the results of simultaneous maternal blood tests . In pregnancies affected by Down syndrome there is a tendency for the levels of human chorionic gonadotropin ( hCG ) to be increased and pregnancy - associated plasma protein A ( PAPP - A ) to be decreased . </P>
normal range for nuchal fold at 12 weeks
normal range for nuchal fold at 12 weeks
2.18 mm
2.18 mm