Is there a nuchal translucency millimeter measurement above which there is no added benefit from first trimester serum screening?

A large group of patients are studied to evaluate whether there is a nuchal translucency (NT) measurement, independent of gestational age, above which immediate diagnostic testing should be offered without waiting for first trimester serum markers. The analysis has shown that during first trimester Down syndrome screening, there is minimal benefit in waiting for serum screening results whenever an NT measurement is 3.0 mm or greater and no benefit for NT of 4.0 mm or greater.