Table 1 Descriptive statistics for quintiles of seasonally and gestational age (20 weeks) adjusted maternal serum 25(OH)D

Covariates

Offspring male sex

4001 (52.0%)

791 (51.4%)

819 (53.3%)

816 (53.1%)

799 (52.0%)

776 (50.5%)

0.52

Parity

 < 0.001

0

3242 (42.2%)

713 (46.4%)

677 (44.0%)

631 (41.0%)

607 (39.5%)

614 (39.9%)

1

2527 (32.9%)

458 (29.8%)

498 (32.4%)

511 (33.2%)

531 (34.5%)

529 (34.4%)

2 + 

1430 (18.6%)

247 (16.1%)

277 (18.0%)

293 (19.1%)

304 (19.8%)

309 (20.1%)

Missing

490 (6.4%)

120 (7.8%)

86 (5.6%)

103 (6.7%)

96 (6.2%)

85 (5.5%)

Any maternal smoking at 18-week gestation

1935 (26.4%)

481 (33.2%)

432 (29.4%)

366 (25.2%)

330 (22.5%)

326 (22.0%)

 < 0.001

Maternal highest educational qualification

0.024

Vocational

702 (9.1%)

131 (8.5%)

149 (9.7%)

147 (9.6%)

137 (8.9%)

138 (9.0%)

CSE/O level

3824 (49.7%)

791 (51.4%)

773 (50.3%)

755 (49.1%)

778 (50.6%)

727 (47.3%)

A level/degree

2435 (31.7%)

439 (28.5%)

462 (30.0%)

496 (32.2%)

489 (31.8%)

549 (35.7%)

Missing

728 (9.5%)

177 (11.5%)

154 (10.0%)

140 (9.1%)

134 (8.7%)

123 (8.0%)

Financial difficulties in pregnancy

498 (7.3%)

94 (7.0%)

101 (7.4%)

112 (8.2%)

94 (6.8%)

97 (7.0%)

0.66

Maternal manual occupation

1104 (19.5%)

223 (20.7%)

242 (21.7%)

210 (18.2%)

212 (18.5%)

217 (18.4%)

0.12

Maternal age at delivery

28.1 (4.8)

27.3 (5.0)

27.6 (4.9)

28.2 (4.9)

28.4 (4.7)

28.8 (4.7)

 < 0.001

Maternal pre-pregnancy BMI

22.9 (3.8)

22.9 (4.0)

23.0 (4.0)

23.1 (3.9)

22.8 (3.6)

22.7 (3.6)

0.13

Exposure

Maternal 25(OH)D (nMol/L) adjusted to 7 weeks ^b

64.1 (32.0)

34.8 (10.9)

50.6 (14.3)

61.5 (18.6)

73.4 (23.4)

100.3 (38.4)

 < 0.001

Maternal 25(OH)D (nMol/L) adjusted to 20 weeks ^b

64.6 (31.7)

29.3 (6.4)

45.2 (4.0)

58.9 (4.2)

75.6 (5.9)

114.1 (26.1)

 < 0.001

Maternal 25(OH)D (nMol/L) adjusted to 34 weeks ^b

69.8 (34.1)

37.3 (12.5)

55.0 (16.7)

67.9 (22.2)

81.7 (27.6)

107.0 (36.3)

 < 0.001

Maternal Standardised Genetic 25(OH)D score ^b

−0.0 (1.0)

−0.1 (1.0)

−0.0 (1.0)

−0.1 (1.0)

0.1 (1.0)

0.1 (1.0)

 < 0.001

Offspring Standardised Genetic 25(OH)D score ^b

0.0 (1.0)

−0.1 (1.0)

−0.1 (1.0)

0.0 (1.0)

0.1 (1.0)

0.1 (1.0)

0.010

Outcome

Diagnosed Autism

93 (1.2%)

18 (1.2%)

17 (1.1%)

22 (1.4%)

23 (1.5%)

13 (0.8%)

0.47

Social Communication Trait

789 (17.0%)

159 (18.9%)

156 (17.0%)

164 (17.0%)

155 (16.4%)

155 (16.1%)

0.58

Speech Coherence Trait

683 (15.5%)

136 (17.4%)

140 (16.1%)

138 (15.0%)

122 (13.4%)

147 (15.7%)

0.21

Repetitive Behaviour Trait

1251 (27.6%)

258 (30.7%)

247 (27.9%)

236 (25.6%)

268 (28.1%)

242 (26.2%)

0.14

Sociability Temperament Trait

614 (10.8%)

125 (11.5%)

113 (10.2%)

139 (12.0%)

114 (9.7%)

123 (10.6%)

0.37

Autism factor mean score ^b

−0.0 (1.0)

0.1 (1.1)

0.0 (1.0)

−0.0 (0.9)

−0.0 (1.0)

−0.0 (1.0)

0.039

Auxiliary variables

Home ownership status

 < 0.001

Owned/mortgaged

5406 (70.3%)

987 (64.2%)

1050 (68.3%)

1110 (72.2%)

1113 (72.4%)

1146 (74.6%)

Council rented

1057 (13.7%)

255 (16.6%)

228 (14.8%)

206 (13.4%)

202 (13.1%)

166 (10.8%)

Privately rented

565 (7.3%)

138 (9.0%)

141 (9.2%)

88 (5.7%)

98 (6.4%)

100 (6.5%)

Other

248 (3.2%)

56 (3.6%)

48 (3.1%)

59 (3.8%)

41 (2.7%)

44 (2.9%)

Missing

413 (5.4%)

102 (6.6%)

71 (4.6%)

75 (4.9%)

84 (5.5%)

81 (5.3%)

Marital status

 < 0.001

Never married

1359 (17.7%)

334 (21.7%)

316 (20.5%)

252 (16.4%)

231 (15.0%)

226 (14.7%)

Previously married (currently unmarried)

429 (5.6%)

78 (5.1%)

96 (6.2%)

100 (6.5%)

72 (4.7%)

83 (5.4%)

1st marriage

5033 (65.5%)

940 (61.1%)

961 (62.5%)

1008 (65.5%)

1077 (70.0%)

1047 (68.1%)

2nd or 3rd marriage

475 (6.2%)

83 (5.4%)

93 (6.0%)

101 (6.6%)

82 (5.3%)

116 (7.5%)

Missing

393 (5.1%)

103 (6.7%)

72 (4.7%)

77 (5.0%)

76 (4.9%)

65 (4.2%)