Nuchal scan or NT/NB scan is done between 11-13 weeks 6 days.It is screening test for ruling out chromosomal, cardiac , skeletal problems..It has to be done by certified radiologist following all protocols, otherwise the whole purpose is defeated .Get your scan by certified radiologist at Rahul gera diagnostic center.. It is premier ultrasound center in south delhi safdarjung enclave green park area. visit www.ultrasound5d.com