Table 2.

Relationship between covariates and maternal Vitamin B12 levels (≥/< median) among controls

Covariates	Maternal Vitamin B12		Maternal Vitamin B12			P-value
	≥ Median		< Median
	Mean	SD	Mean	SD	t
Maternal age (years)	29.52	5.20	29.58	5.41	0.18	0.85
Gestational week of blood draw	10.19	2.89	11.06	3.21	4.58	<0.001
	N	%	N	%	χ 2
Previous births
0	191	37.23	209	40.74	1.32	0.25
≥1	322	62.77	304	59.26
History of maternal ADHD diagnosis a					1.00	0.50
No	512	99.81	513	100
Yes	1	0.19	0	0
History of maternal substance abuse b					0	1.00
No	506	98.64	506	98.64
Yes	7	1.36	7	1.36
History of maternal psychopathology c					0.452	0.50
No	455	88.69	448	87.33
Yes	58	11.31	65	12.67
History of paternal ADHD diagnosisa*1					1.0	0.49
No	511	100	507	99.80
Yes	0	0	1	0.20
History of paternal psychopathologyd*1					0.003	0.95
No	443	86.69	441	86.81
Yes	68	13.31	67	13.19
Maternal smoking 2					0.12	0.72
No	432	86.57	434	87.32
Yes	67	13.43	63	12.68
Maternal SES					10.24	0.03
Upper white collar	71	13.84	67	13.06
Lower white collar	213	41.52	234	45.61
Blue collar	106	20.66	77	15.01
Others	68	13.26	91	17.74
Missing	55	10.72	44	8.58
Gestational age (weeks) 3					0.24	0.62
<37	19	3.71	22	4.31
≥37	493	96.29	488	95.69
Weight for gestational age 3					1.33	0.51
<−2 SD	10	1.95	13	2.55
−2 SD to +2 SD	480	93.75	481	94.31
>+2 SD	22	4.30	16	3.14
Maternal immigration status					0.10	0.28
No	511	99.61	507	98.83
Yes	2	0.39	6	1.17

^aICD-10: F90.X or ICD-9: 314.X,

^bICD-8 (291, 303, 304), ICD-9 (291, 292, 303,304,305) or ICD-10 (F10–19);

^cICD-8 (291–308), ICD-9 (291–316) or ICD-10 (F10–99, excluding mental retardation (F70–79) excluding maternal substance abuse diagnosis,

^dICD-8 (291–308), ICD-9 (291–316) or ICD-10 (F10–99, excluding mental retardation (F70–79).

¹Data missing for 7 controls;

²Data missing for 30 controls; Data missing for 4 controls; SD: standard deviation; t: t-test value; χ²: Pearson’s chi squared test value.