AC by gestational age							
							
weeks	-1.64SD	-1.5SD	-1.28SD	mean	+1.28SD	+1.5SD	+1.64SD
16	9.3	9.5	9.7	10.9	12.2	12.4	12.5
17	10.3	10.4	10.6	12.0	13.3	13.5	13.6
18	11.2	11.4	11.6	13.0	14.3	14.6	14.7
19	12.2	12.3	12.6	14.0	15.4	15.7	15.8
20	13.1	13.3	13.5	15.1	16.5	16.8	16.9
21	14.0	14.2	14.5	16.1	17.6	17.8	18.0
22	15.0	15.1	15.4	17.1	18.6	18.9	19.1
23	15.9	16.1	16.4	18.1	19.7	20.0	20.2
24	16.8	17.0	17.3	19.1	20.8	21.1	21.2
25	17.7	17.9	18.2	20.1	21.8	22.1	22.3
26	18.6	18.8	19.1	21.0	22.8	23.1	23.3
27	19.5	19.7	20.0	22.0	23.8	24.2	24.4
28	20.3	20.5	20.9	22.9	24.8	25.2	25.4
29	21.1	21.4	21.7	23.8	25.8	26.1	26.4
30	22.0	22.2	22.5	24.7	26.7	27.1	27.3
31	22.8	23.0	23.4	25.6	27.7	28.1	28.3
32	23.5	23.8	24.2	26.5	28.6	29.0	29.2
33	24.3	24.5	24.9	27.3	29.5	29.9	30.1
34	25.0	25.3	25.7	28.1	30.3	30.7	31.0
35	25.7	26.0	26.4	28.9	31.2	31.6	31.9
36	26.4	26.6	27.1	29.7	32.0	32.4	32.7
37	27.0	27.3	27.7	30.4	32.8	33.2	33.5
38	27.6	27.9	28.4	31.1	33.5	34.0	34.3
39	28.2	28.5	29.0	31.8	34.2	34.7	35.0
40	28.8	29.1	29.5	32.4	34.9	35.4	35.7
41	29.3	29.6	30.0	33.0	35.6	36.1	36.4
42	29.7	30.1	30.5	33.6	36.2	36.7	37.0