Table 1.

Characteristics of study participants.

Variable	Groups	Cases 109	%	Control 252	%	OR a	95% CI	P-value
Child´s sex	Female	57	52.3	100	39.7	1.66	1.05-2.62	0.026
	Male	52	47.7	152	60.3
Child´s age (months) at diagnosis/recruitment	≤ 12	34	31.2	73	29.0	1.11	0.68-1.81	0.671
	>12 a	75	68.8	179	71.0
Birth weight (grams)	≤3,500a	92	84.4	217	86.1
	>3,500	17	15.6	35	13.9	1.14	0.61-2.14	0.671
Breastfeeding	Yes	96	88.1	226	89.7	0.84	0.42-1.72	0.651
	No	13	11.9	26	10.3
Breastfeeding duration (months)	≤6	55	57.3	99	43.8	0.58	0.35-0.94	0.026
	>6	41	42.7	127	56.2
Maternal age at pregnancy (years)	<35	97	89.0	231	91.7
	≥35	12	11.0	21	8.3	1.36	0.64-2.87	0.417
Mother´s education (years)	0-9	56	51.4	120	47.6	1.30	0.79-2.16	0.301
	9.1-12.9 a	34	31.2	95	37.7	Ref.
	≥13	19	17.4	37	14.7	1.43	0.73-2.83	0.295
Smoking 1 year prior to pregnancy	Yes	31	28.4	77	30.6	0.90	0.55-1.48	0.686
	No	78	71.6	175	69.4
Smoking during pregnancy	Yes	4	3.7	7	2.8	1.33	0.38-4.65	0.650
	No	105	96.3	245	97.2
Alcohol during pregnancy	Yes	4	3.7	31	12.3	0.27	0.09-0.79	0.010
	No	105	96.3	221	87.7
Iron during pregnancy	Yes	76	69.7	216	85.7	0.38	0.22-0.66	0.000
	No	33	30.3	36	14.3
Vitamins during pregnancy	Yes	98	89.9	238	94.4	0.52	0.23-1.19	0.119
	No	11	10.1	14	5.6
Minerals during pregnancy	Yes	4	3.7	16	6.3	0.56	0.18-1.72	0.307
	No	105	96.3	236	93.7
Drug use for genital infection during pregnancy	Yes	15	13.8	34	13.5	1.02	0.53-1.97	0.945
	No	94	86.2	218	86.5
Paternal age at pregnancy (years)	<35	82	75.2	198	78.6
	≥35	27	24.8	54	21.4	1.21	0.71-2.05	0.488
Father´s education (years)	0-9	53	48.6	138	54.7	0.82	0.49-1.37	0.454
	9.1-12.9 a	35	32.1	75	29.8	Ref.
	≥13	21	19.3	39	15.5	1.15	0.59-2.24	0.673
Smoking 1 year prior to pregnancy	Yes	48	47.1	141	58.0	0.64	0.40-1.02	0.061
	No	61	52.9	111	42.0
Place of residence	Mexico City	42	38.5	132	52.4	0.57	0.36-0.90	0.016
	State of Mexico	67	61.5	120	47.6
Health institution	Ministry of health*	62	56.9	164	65.1	1.41	0.89-2.24	0.139
	IMSS¥	47	43.1	88	34.9
Overcrowding index ‡	Low SES (≥1.6)	15	13.8	23	9.1	1.59	0.79-3.18	0.188
	Moderate-High SES (<1.6) a	94	86.2	229	90.9

^a OR crude.

^aReference level. The selection was based on the CLIC analysis, and schooling <9 years was considered the high-risk or low socioeconomic level category. If a mother had a level of schooling higher than high school, it was considered that it could potentially have a protective effect, so these strata were left out and the intermediate group was considered as the reference value.

*Includes Secretary of Health, Secretary of Health of Mexico City, State of Mexico Institute of Health (ISEM, by its acronym in Spanish), Institute of Security and Social Services for State Workers (ISSSTE, by its acronym in Spanish).

¥ Mexican Institute of Social Security.

‡ It was calculated by number of persons per bedroom as socioeconomic level.