The NT measurement is only a strong predictor of chromosomal abnormality if measured between 12-13 weeks. That's why 1st trimester screening (combined NT, BhCG and PAPPA) is done at that time.
Even my surrodaughter's NT measurement, which was >7 mm at 12.5 weeks, had gone down to a "normal" measurement by 20 weeks. I had weekly u/s and monthly level II u/s throughout my pregnancy. As babies grow, so does their neck.
You have absolutely nothing to worry about.
1st + HPT 5dp5dt
beta 9dp5dt -- 120
beta 11dp5dt -- 323
Amelia with Trisomy 18 b. 03/01/2007, d.03/02/2007