Analysis models for variables associated with
					breastfeeding duration

A population-based cohort study was conducted with 86 mothers and newborns from two areas primary covered by the National Health System, with high rates of infant mortality in Vitória, Espírito Santo, Brazil. During 30 months, 67 (78%) children and mothers were visited seven times at home by trained interviewers, who filled out survey forms. Data on food and sucking habits, socioeconomic and maternal characteristics were collected. Variables were analyzed by Cox regression models, considering duration of breastfeeding as the dependent variable, and logistic regression (dependent variables, was the presence of a breastfeeding child in different post-natal ages).

RESULTS

In the logistic regression model, the pacifier sucking (adjusted Odds Ratio: 3.4; 95%CI 1.2-9.55) and bottle feeding (adjusted Odds Ratio: 4.4; 95%CI 1.6-12.1) increased the chance of weaning a child before one year of age. Variables associated to breastfeeding duration in the Cox regression model were: pacifier sucking (adjusted Hazard Ratio 2.0; 95%CI 1.2-3.3) and bottle feeding (adjusted Hazard Ratio 2.0; 95%CI 1.2-3.5). However, protective factors (maternal age and family income) differed between both models.

CONCLUSIONS

Risk and protective factors associated with cessation of breastfeeding may be analyzed by different models of statistical regression. Cox Regression Models are adequate to analyze such factors in longitudinal studies.

maternal and child health; breast feeding; cohort studies

	Yes (%)	No (%)	p-value	OR	95%CI	p-value	AOR	95%CI
Breastfeeding>3 months (n=81) – LRM(1)
Pacifier sucking (onset until 1^st month)	2 (12.5)	27 (41.5)
Other artificial nipples (onset until 6^th month)	1 (6.3)	37 (56.9)	0.001	19.82	2.47–426.13	0.005	20.517	2.51–168.77
Breastfeeding ≥6 months (n=80) – LRM (2)
Bottle feeding (onset until 1^st month)	12 (20.0)	15 (75.0)
Bottle feeding (onset until 6^th month)	36 (60.0)	20 (100.)	0.002	–	Indefinido
Pacifier sucking (onset until 1^st month)	16 (26.7)	13 (65.0)	0.005	5.11	1.54–17.48	0.037	4.092	1.09–15.34
Pacifier sucking (onset until 3^rd month)	22 (36.7)	14 (77.8)	0.005	6.05	1.58–25.13
Pacifier sucking (onset until 6^th month)	26 (43.3)	15 (83.3)	0.006	6.54	1.53–32.01
Bottle use (onset until 1^st month)	14 (23.30	15 (75.0)	0.000	9.86	2.69–38.31
Bottle use (onset until 3^rd month)	19 (31.7)	18 (100.)	0.000	–	Indefinido
Bottle use (onset until 6^th month)	35 (58.3)	18 (100.)	0.002	–	Indefinido
Teeth eruption (until 6^th month)	24 (40.0)	3 (15.8)	0.096	0.28	0.06–1.19	0.024	6.538	1.27–33.54
Separated parents	16 (26.7)	10 (50.0)	0.098	2.75	0.86–8.92
Breastfeeding ≥12 months (n=81) – LRM (3)
Bottle feeding (onset until 1^st month)	9 (19.1)	18 (52.9)
Bottle feeding (onset until 6^th month)	27 (57.4)	30 (88.2)	0.006	5.56	1.52–22.13
Pacifier sucking (onset until 1^st month)	11 (23.40	18 (52.9)	0.012	3.68	1.28–10.74	0.005	4.351	1.56–12.13
Pacifier sucking (onset until 3^rd month)	14 (29.8)	22 (68.8)	0.001	5.19	1.77–15.59
Pacifier sucking (onset until 6^th month)	16 (34.0)	25 (78.1)	0.000	6.92	2.22–22.39
Bottle use (onset until 1^st month)	11 (23.4)	18 (52.9)	0.012	3.68	1.28–10.74
Bottle use (onset until 3^rd month)	14 (29.8)	23 (71.9)	0.001	6.02	2.02–18.54
Bottle use (onset until 6^th month)	26 (55.3)	28 (87.5)	0.006	5.65	1.54–22.59
Maternal age (> 35 years)	8 (17.0)	0 ( 0.0)	Fisher	0.018	Indefinido	0.002	0.215	0.08–0.58

Variable	Category	Breastfeeding duration
Variable	Category	Mean	Median	Log-rank	p-value
		(95%CI)	(95%CI)
Bottle feeding (onset until 1^st month)	Yes No	9(6-13) 18(16-21)	4(3-5) 18(13-23)	10.2500	0.0014
Bottle feeding (onset until 6^th month)	Yes No	13(10-16) 21(18-24)	10(5-15) 23(21-25)	5.6200	0.0178
Pacifier sucking (onset until 1^st month)	Yes No	12(8-16) 17(14-20)	9(3-15) 18(13-23)	2.7600	0.0964
Pacifier sucking (onset until 3^rd month)	Yes No	12(9-15) 19(16-22)	9(6-12) 19(15-23)	4.7600	0.0275
Pacifier sucking (onset until 6^th month)	Yes No	12(9-15) 20(16-23)	9(6-12) 19(14-24)	7.5200	0.0061
Bottle use (onset until 1^st month)	Yes No	10(6-14) 18(16-21)	4(0-10) 18(10-26)	9.8500	0.0017
Bottle use (onset until 3^rd month)	Yes No	10(7-13) 21(18-23)	6(2-10) 23(20-26)	18.1100	0.0000
Bottle use (onset until 6^th month)	Yes No	13(10-16) 22(19-25)	10(6-14) 24(23-25)	6.8700	0.0087
Monthly family income (in minimum wages)	≤2 wages >2 wages	17 (14–20) 13 (10–16)	20 (13–27) 12 (7–17)	3.4400	0.0635

Models	Co-variables	Estimate	Standard error	Wald	p-value	HR	95%CI
Cox regression (1)*	Bottle feeding (onset until 1^st month)	0.89	0.27	11.23	0.00	2.43	1.45	4.10
Cox regression (1)*	Monthly family income (< 2 minimum wages)	-0.58	0.25	5.30	0.02	0.56	0.34	0.92
Cox regression (2)*	Bottle feeding (onset until 1^st month)	0.70	0.28	6.26	0.01	2.01	1.16	3.47
Cox regression (2)*	Pacifier sucking (onset until 6^th month)	0.54	0.26	4.27	0.04	1.72	1.03	2.88
Cox regression (3)*	Monthly family income (< 2 minimum wages)	-0.61	0.25	5.79	0.02	0.54	0.33	0.89
	Pacifier sucking (onset until 6^th month)	0.68	0.26	7.04	0.01	1.97	1.19	3.26
	Monthly family income (up to two minimum wages)	-0.53	0.25	4.51	0.03	0.59	0.36	0.96

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[1] Endereço para correspondência: Edson Theodoro dos S. Neto Rua Guilherme Bassini, 97 CEP 29030-015 - Vitória/ES E-mail: edsontheodoro@uol.com.br