Table 2

Odds ratios (OR*) of more severe versus mild cases by Z-score band

Z-score bandOverall proportion more severe
Equivalent centiles:<−1.88
<3%
OR (n†)
−1.88 to <−1.28
3 to <10%
OR (n)
−1.28 to <−0.67
10 to <25%
OR (n)
−0.67 to <0
25 to <50%
OR (n)
0 to <0.67
50 to <75%
OR (n)
0.67 to <1.28
75 to <90%
OR (n)
1.28 to <1.88
90 to <97%
OR (n)
⩾1.88
⩾97%
OR (n)
*Odds ratio by comparison to the reference band 0.67 to <1.28 Z-score. Bold, p < 0.01.
†n = more severe + mild cases (for n more severe cases only see table 1). For instance, the OR for being a more severe rather than a mild case (all gestations) with a birth weight Z-score <−1.88 is (271/(532–271))/(101/(249–101)) = 1.52 [99% CI 1.02 to 2.27].
All gestations1.5 (532)1.7 (404)1.2 (584)1.2 (611)1.3 (476)1 (249)1.4 (135)1.5 (131)0.48
Preterm1.4 (247)1.4 (157)1.1 (223)1.1 (259)1.2 (179)1 (87)1.2 (54)1.4 (59)0.52
Term1.6 (285)1.8 (247)1.3 (361)1.2 (352)1.4 (297)1 (162)1.5 (81)1.4 (72)0.45
Bilat spastic1.3 (390)1.3 (277)1.4 (354)1.2 (371)1.5 (257)1 (143)1.2 (81)1.3 (77)0.65
Hemiplegic1.6 (144)2.9 (108)1.4 (184)1.4 (197)1.4 (168)1 (87)1.9 (40)1.4 (33)0.10
Males1.7 (328)1.9 (239)1.5 (328)1.3 (348)1.4 (286)1 (134)1.4 (65)1.6 (75)0.47
Females1.4 (204)1.4 (165)1.0 (256)1.2 (263)1.3 (190)1 (115)1.3 (70)1.3 (56)0.49
More severe intellectual impairment (IQ <50)
All gestations1.5 (540)1.6 (414)1.3 (591)1.1 (618)1.2 (480)1 (251)1.3 (137)1.1 (135)0.28
Walking impairment (not walking independently)
All gestations1.4 (730)1.3 (510)1.1 (738)1.1 (802)1.2 (658)1 (345)1.3 (197)1.2 (203)0.45