Gestational age by FL mm mm 20 16 w 1 d ± 6 d 51 28 w 5 d ± 10 d 21 16 w 3 d ± 6 d 52 29 w 2 d ± 11 d 22 16 w 6 d ± 6 d 53 29 w 5 d ± 11 d 23 17 w 1 d ± 7 d 54 30 w 2 d ± 11 d 24 17 w 3 d ± 7 d 55 30 w 5 d ± 11 d 25 17 w 6 d ± 7 d 56 31 w 2 d ± 11 d 26 18 w 1 d ± 7 d 57 31 w 6 d ± 11 d 27 18 w 3 d ± 7 d 58 32 w 3 d ± 11 d 28 18 w 6 d ± 7 d 59 33 w 0 d ± 12 d 29 19 w 1 d ± 7 d 60 33 w 3 d ± 12 d 30 19 w 4 d ± 8 d 61 34 w 0 d ± 12 d 31 20 w 0 d ± 8 d 62 34 w 4 d ± 12 d 32 20 w 2 d ± 8 d 63 35 w 1 d ± 12 d 33 20 w 5 d ± 8 d 64 35 w 5 d ± 12 d 34 21 w 1 d ± 8 d 65 36 w 2 d ± 12 d 35 21 w 3 d ± 8 d 66 37 w 0 d ± 12 d 36 21 w 6 d ± 8 d 67 37 w 4 d ± 13 d 37 22 w 2 d ± 9 d 68 38 w 1 d ± 13 d 38 22 w 5 d ± 9 d 69 38 w 5 d ± 13 d 39 23 w 1 d ± 9 d 70 39 w 3 d ± 13 d 40 23 w 4 d ± 9 d 41 24 w 0 d ± 9 d 42 24 w 3 d ± 9 d 43 24 w 6 d ± 9 d 44 25 w 3 d ± 9 d 45 25 w 6 d ± 10 d 46 26 w 2 d ± 10 d 47 26 w 5 d ± 10 d 48 27 w 2 d ± 10 d 49 27 w 5 d ± 10 d 50 28 w 2 d ± 10 d