Additional file 1: of Reference ranges for foetal nasal bone length, prenasal thickness, and interocular distance at 18 to 24 weeks’ gestation in low-risk pregnancies AltunkeserAyşegül KörezM. 2017 Percentile Values for NBL, PNT, IOD and PNT/NBL Ratio According to Gestational Weeks. (DOCX 12 kb)