Table 2. Incidence Rates and HRs of Epilepsy According to Maternal Early Pregnancy BMI .

Characteristic	No. of Children	Child-years of Follow-up	No. of Casesa	Rate per 10 000 Child-years	HR (95% CI)
					Unadjustedb	Adjustedc
Maternal BMI
<18.5	30 733	240 213	152	6.33	1.01 (0.85-1.19)	1.00 (0.85-1.18)
18.5-<25.0	786 811	6 163 602	3880	6.3	1 [Reference]	1 [Reference]
25.0-<30.0	315 486	2 430 474	1739	7.15	1.13 (1.07-1.20)	1.11 (1.04-1.17)
30.0-<35.0	99 737	740 447	590	7.97	1.26 (1.15-1.37)	1.20 (1.10-1.31)
35.0-<40.0	29 837	214 899	187	8.7	1.36 (1.18-1.58)	1.30 (1.12-1.50)
≥40.0	10 374	71 613	89	12.4	1.94 (1.56-2.40)	1.82 (1.46-2.26)
Missing	148 573	13 15 139	955	7.26
P value for trendd					<.001	<.001
Hazard difference per unit BMI, %					2.4 (1.8-2.9)	2.0 (1.5-2.6)

Abbreviations: BMI, body mass index (calculated as weight in kilograms divided by height in meters squared); HR, hazard ratio.

^aNumber of epilepsy diagnoses by age: younger than 2 years, 2097 (27.6%); 2 to younger than 4 years, 1434 (18.9%); 4 to younger than 6 years, 1346 (17.7%); 6 to younger than 8 years, 993 (13.1%); 8 to younger than 10 years, 829 (10.9%); and 10 years or older, 893 (11.8%). Median age at diagnosis was 4.0 years (interquartile range, 1-7 years). The last case was diagnosed when the patient was 16 years.

^bFrom a Cox proportional hazards model with age at diagnosis of epilepsy as the outcome. Analyses included 6637 cases among 1 272 978 children.

^cFrom a Cox proportional hazards model adjusted for maternal age, country of origin, educational level, cohabitation with a partner, parity, height, smoking during pregnancy, maternal epilepsy, and year of delivery. Complete case analyses including 6422 cases among 1 228 641 children.

^dWald test when a variable representing ordinal categories of BMI was introduced into the model as a continuous predictor.