Table 3. Normal reference range for the fetal optic nerve width at 19–40 weeks’ gestation.

GA (week)	n	ON width (mm)
		3rd centile	5th centile	50th centile	95th centile	97th centile
19−21	46	1.20	1.20	1.60	1.87	1.90
22−24	26	1.30	1.34	1.75	2.10	2.10
25−27	36	1.70	1.70	2.10	2.60	2.60
28−30	64	2.09	2.10	2.50	2.88	2.90
31−33	48	2.10	2.10	2.60	3.16	3.20
34−36	65	2.70	2.73	3.20	3.76	4.00
37−40	25	3.10	3.13	3.40	4.20	4.30

GA, gestational age; ON, optic nerve.