Nuchal translucent thickness 4.7mm

hi, ive just done my 1st trisemester test and we found out that our baby has NT as thick as 4.7mm which give the chance of 1:18 for down syndrome. has anyone encounter the same and can you share more on what happened? me as a mum to be has been so devastated and cry is the only thing i know for now. my gynea asked us to perform amniocentesis test in about 4 weeks time when im about 16 weeks. any sharing will be appreciate it thank you.