Head circumference (mm)

GA (weeks)

50th centile

5th centile

95th centile

12

68.1

75.1

79.2

13

82.2

70.8

93.6

14

96.0

84.2

107.8

15

109.7

79.5

121.9

16

123.1

110.6

135.7

17

136.4

123.4

149.3

18

149.3

136.0

162.7

19

162.0

148.3

175.7

20

174.5

160.4

188.6

21

186.6

172.1

202.1

22

198.5

183.6

213.3

23

210.0

194.8

225.3

24

221.2

205.6

236.9

25

232.1

216.1

248.1

26

242.6

226.2

259.0

27

252.7

235.9

269.5

28

262.5

245.3

279.6

29

271.8

254.3

289.4

30

280.7

262.8

298.7

31

289.2

270.9

307.6

32

297.3

278.6

316.0

33

304.9

285.8

324.0

34

312.0

292.6

331.5

35

318.7

298.8

338.5

36

324.8

340.6

345.0

37

330.4

309.8

351.0

38

335.5

314.5

356.5

39

340.0

318.7

361.4

40

344.0

322.3

365.8

41

347.4

325.3

369.6

42

350.3

327.7

372.8