Gestational age by AC cm 10.0 15 w 3 d ± 8 d 10.5 16 w 0 d ± 8 d 11.0 16 w 4 d ± 8 d 11.5 17 w 0 d ± 8 d 12.0 17 w 4 d ± 9 d 12.5 18 w 0 d ± 9 d 13.0 18 w 4 d ± 9 d 13.5 19 w 0 d ± 9 d 14.0 19 w 4 d ± 9 d 14.5 20 w 0 d ± 9 d 15.0 20 w 3 d ± 10 d 15.5 21 w 0 d ± 10 d 16.0 21 w 3 d ± 10 d 16.5 22 w 0 d ± 10 d 17.0 22 w 3 d ± 10 d 17.5 22 w 6 d ± 10 d 18.0 23 w 3 d ± 11 d 18.5 23 w 6 d ± 11 d 19.0 24 w 3 d ± 11 d 19.5 24 w 6 d ± 11 d 20.0 25 w 3 d ± 11 d 20.5 25 w 6 d ± 11 d 21.0 26 w 3 d ± 12 d 21.5 27 w 0 d ± 12 d 22.0 27 w 3 d ± 12 d 22.5 28 w 0 d ± 12 d 23.0 28 w 4 d ± 12 d 23.5 29 w 0 d ± 12 d 24.0 29 w 4 d ± 13 d 24.5 30 w 1 d ± 13 d 25.0 30 w 5 d ± 13 d 25.5 31 w 2 d ± 13 d 26.0 31 w 6 d ± 13 d 26.5 32 w 3 d ± 13 d 27.0 33 w 1 d ± 13 d 27.5 33 w 5 d ± 14 d 28.0 34 w 2 d ± 14 d 28.5 35 w 0 d ± 14 d 29.0 35 w 4 d ± 14 d 29.5 36 w 2 d ± 14 d 30.0 36 w 0 d ± 14 d 30.5 37 w 5 d ± 14 d 31.0 38 w 2 d ± 15 d 31.5 39 w 0 d ± 15 d 32.0 39 w 6 d ± 15 d 32.5 40 w 4 d ± 15 d 33.0 41 w 2 d ± 15 d