Table 1.

Characteristics of the Participants at Delivery and First Follow-up Visit, Tapachula, Chiapas, Mexico 2002-2005

	Follow-up status			At least one follow-up visit
Characteristics	Followed (n=788) %	Lost to follow-up (n=81) %	P valuea	One visit (n=39) %	2+ visits (n=749) %	P valuea
Maternal
Age at childbirth (y)b	23.7 (7.1)	21.5 (6.0)	0.01	23.7 (7.5)	23.7 (7.0)	0.45
Education (y)			0.02			0.04
None	4.2	6.2		5.1	4.1
1 - 6	30.7	46.9		25.6	31.0
7 - 9	31.0	25.9		15.4	31.8
10 - 12	24.0	13.6		43.6	23.0
>12	10.2	7.4		10.3	10.1
Pre-pregnancy BMI (kg/m2)c			0.90			0.99
≤18.5	7.2	4.9		7.7	7.2
18.6 - <25.0	57.5	46.9		56.4	57.5
25.0 - <30.0	25.3	16.0		25.6	25.2
≥30	10.0	6.2		10.3	10.0
Smoked during pregnancy	1.1	1.2	0.63	0.0	1.2
Drank alcohol during pregnancyc	2.9	4.9	0.24	7.7	2.7	0.10
First prenatal care visit			<0.01			0.51
None	36.0	55.6		43.6	35.6
First trimester	42.6	24.7		41.0	42.7
After first  trimester	21.3	19.8		15.4	21.6
Parityde			0.28			0.07
1	41.4	46.9		56.4	40.6
2	34.9	37.0		33.3	35.0
3+	23.7	16.0		10.3	24.4
Age at menarche (y)bc	13.0 (2.0)	13.0 (2.0)	0.40	13.0 (2.0)	13.0 (2.0)	0.88
Height (cm)b	152.5 (7.7)	151.4 (8.1)	0.04	149.9 (7.5)	152.6 (7.8)	0.05
Serum p,p’-DDE (μg/g)bf	2.7 (4.3)	1.7 (3.8)	0.01	1.6 (2.4)	2.7 (4.6)	<0.01
Serum p,p’-DDT (μg/g)bf	0.3 (0.6)	0.2 (0.5)	<0.01	0.2 (0.2)	0.3 (0.7)	<0.01
Worked outside homee	31.5	35.8	0.43	33.3	31.4	0.80
Hospital of recruitment			<0.01			0.68
Social Security	49.4	28.4		46.2	49.5
Ministry of Health	50.6	71.6		53.8	50.5
Residence areae			0.81			0.29
Urban	59.4	58.0		51.3	59.8
Rural	40.6	42.0		48.7	40.2
Poverty indexceg			0.07			0.86
Poorest	70.7	66.7		66.7	70.9
Less poor	19.0	11.1		20.5	19.0
Not poor	10.2	2.5		10.3	10.1
Home ownerc				17.9	35.9	0.18
Child
Gestational age (wk)b	40.0 (1.0)	39.0 (1.0)	0.13	39.7 (2.0)	40.0 (1.0)	0.09
Birth season			0.51			0.38
Winter	20.1	14.8		28.2	19.6
Spring	28.8	35.8		33.3	28.6
Summer	28.0	27.2		23.1	28.3
Autumn	23.1	22.2		15.4	23.5
Age at introduction of formula or cow’s milk (mo)bgh				6.0 (8.5)	3.0 (7.5)	0.06
Breastfeed everh				97.4	98.7	0.43
Ever exclusively breastfeedh				89.7	83.3	0.29
Duration of any breastfeeding (mo)bh				10.0 (9.8)	11.0 (12.9)	0.08
Duration of exclusive breastfeeding (mo)bh				0.1 (2.0)	0.1 (1.0)	0.86
Age at introduction of grains and cereal (mo)bh				7.0 (6.0)	6.0 (3.0)	0.02
Number of older siblings			0.22			<0.01
0	43.0	53.1		59.0	42.2
1	36.3	30.9		38.5	36.2
2+	20.7	16.0		2.6	21.6
Had a younger sibling during follow-uph				7.7	10.0	0.11

Abbreviations: BMI, body mass index; DDE, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene; DDT, 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane

^aComparing subjects by follow-up status (followed vs. lost to follow-up) and those with at least one visit (one vs. 2+ visits) using Pearson’s chi-squared or Fisher’s exact tests for categorical and Kruskal-Wallis equality-of-populations rank test for continuous variables. All tests were two-sided

^bMedian (interquartile range)

^cVariables with missing data: ≤ 2.5%, except for mother’s pre-pregnancy BMI (25.9%), age at menarche (49.4%), and poverty index (19.8%) in the lost to follow-up group

^dParity of one at recruitment reflects the birth of the study child

^eTime-varying variables, information for those with at least one follow-up visit reflects their status at first visit

^fDetermined from maternal serum samples drawn at delivery of the study child

^gDefined using Mexican national standards based on monthly per capita income: Urban (Poorest, ≤672 pesos; Less poor, >672 to ≤1,367; Not poor, >1,367) and Rural (Poorest, ≤ 495; Less poor, >495 to ≤946; Not poor, >946) (Cupul-Uicab et al., 2008)

^hThe information was asked only in the follow-up study