Table 2.

Incidence of infant mortality and adjusted incidence rates of the determinants analyzed according to birth weight strata

	Crude analysis		Adjusted analysis	Crude analysis		Adjusted analysis	Crude analysis		Adjusted analysis
	Mortality rate (%)	P	IR (CI 95%) adj*	Mortality rate (%)	P	IR (CI 95%) adj*	Mortality rate (%)	P	IR (CI 95%) adj*
	500–900 g			1000–1499 g			1500–2499 g
Biological determinants
Maternal age
10–17 years	66.67	0.0153	0.93 (0.81;1.07)	19.67	0.0003	1.74 (1.15;2.65)	2.19	0.0106	1.40 (0.94;2.08)
≥ 35 years	42.37	0.0002	0.87 (0.74;1.02)	7.44	0.0512	0.78 (0.53;1.16)	1.48	0.8815
18–34 years	56.79		1	10.79		1	1.44		1
Gender
Male	59.85	0.0006	1.16 (1.05;1.27)	12.26	0.0563	1.29 (1.00;1.66)	1.72	0.0466	1.07 (0.85;1.35)
Female	50.37		1	9.66		1	1.37		1
Gestational age
< 22 weeks	92.50	< 0.0001	1.59 (1.29;1.96)	+
22–27 weeks	63.19	< 0.0001	1.43 (1.23;1.66)	23.18	< 0.0001	1.90 (1.27;2.84)	+
28–31 weeks	35.60		1	11.24	0.0099	1.27 (0.93;1.73)	5.03	< 0.0001	3.06 (2.03;4.61)
32–36 weeks	+			7.48		1	1.62	0.0008	1.48 (1.13;1.94)
≥ 37 weeks	+			+			1.05		1
5-min Apgar Index
< 7	75.68	< 0.0001	1.43 (1.29;1.59)	28.46	< 0.0001	2.90 (2.21;3.81)	11.36	< 0.0001	6.3 (4.61;8.71)
≥ 7	40.18		1	7.78		1	1.21		1
Skin color of the mother
Black/Brown/Asian/Indigenous	62.86	0.0006	1.02 (0.92;1.14)	11.44	0.6284		1.82	0.0722	0.89 (0.68;1.18)
White	52.49		1	10.67			1.45		1
Social determinants
Maternal schooling
None/< 8 years	65.60	< 0.0001	1.11 (0.94;1.32)	15.07	0.0002	0.83 (0.55;1.25)	2.32	< 0.0001	1.65 (1.06;2.58)
8–11 years	54.70	0.0001	1.01 (0.86;1.19)	9.08	0.3674		1.18	0.0598	1.12 (0.72;1.72)
≥ 12 years	39.73		1	7.64		1	0.83		1
Previous living children
1	51.05	0.7130		11.49	0.0320	1.41 (1.00;1.98)	1.56	0.0620	1.26 (0.91;1.75)
2	63.97	0.0060	1.13 (0.97;1.31)	15.94	< 0.0001	2.28 (1.55;3.35)	1.67	0.0560	1.20(0.79;1.80)
≥ 3	65.34	0.0001	1.07 (0.91;1.25)	15.00	< 0.0001	1.72 (1.13;2.63)	2.63	< 0.0001	1.43 (0.97;2.11)
Nenhum	52.34		1	8.12		1	1.18		1
Previous deceased children
≥ 1	55.17	0.9570		7.80	0.0808	0.64 (0.40;1.03)	1.93	0.1333	1.19 (0.82;1.71)
None	54.96		1	11.35		1	1.49		1
Health care determinants
Prenatal visits
None	76.79	< 0.0001	1.03 (0.84;1.26)	16.86	< 0.0001	1.41 (0.84;2.37)	3.40	< 0.0001	2.38 (1.54;3.68)
1–3	61.48	< 0.0001	1.00 (0.82;1.21)	14.79	< 0.0001	1.65 (1.05;2.60)	2.70	< 0.0001	2.14 (1.47;3.12)
4–6	48.0	0.0012	0.92 (0.75;1.13)	10.95	0.0001	1.60 (1.02;2.49)	1.59	< 0.0001	1.49 (1.06;2.08)
≥ 7	34.55		1	4.82		1	0.85		1
Type of delivery
Cesarean	37.93	< 0.0001	0.74 (0.66;0.84)	8.44	< 0.0001	0.75 (0.56;0.99)	1.46	0.4301
Vaginal	72.34		1	16.02		1	1.60
Type of hospital
Public	65.86	< 0.0001	1.85 (1.41;2.43)	12.05	0.0004	1.56 (0.84;2.88)	1.79	< 0.0001	1.01 (0.62;1.64)
Mixed	47.66	< 0.0001	1.46 (1.10;1.94)	11.30	0.0015	1.45 (0.77;2.74)	1.57	0.0015	0.81 (0.49;1.33)
Private	26.73		1	4.72		1	0.83		1
	2500–2999 g			3000–3999 g			≥ 4000 g
Biological determinants
Maternal age
10–17 years	0.58	0.4529		0.50	< 0.0001	1.56 (1.13;2.14)	0.30	0.9178
≥ 35 years	0.40	0.1821	0.72 (0.51;1.03)	0.16	0.0023	0.63 (0.45;0.88)	0.155	0.2458
18–34 years	0.50		1	0.26		1	0.28
Gender
Male	0.55	0.0886	1.11 (0.89;1.39)	0.30	0.0023	1.29 (1.07;1.57)	0.24	0.5527
Female	0.45		1	0.23		1	0.29
Gestational age
< 22 weeks	+			+			+
22–27 weeks	+			+			+
28–31 weeks	+			+			+
32–36 weeks	0.77	0.0002	1.48 (1.11;1.99)	0.56	0.0005	1.55 (0.92;2.29)	+
≥ 37 weeks	0.45		1	0.26		1	0.26
5-min Apgar Index
< 7	6.81	< 0.0001	12.19 (8.44;17.61)	6.06	< 0.0001	22.28 (17.9;29.06)	9.32	< 0.0001	58.54 (28.67;119.50)
≥ 7	0.44		1	0.22		1	0.17		1
Skin color of the mother
Black/Brown/Asian/Indigenous	0.82	< 0.0001	1.30 (1.02;1.67)	0.43	< 0.0001	1.28 (1.05;1.57)	0.37	0.1162	1.53 (0.76;3.09)
White	0.40		1	0.22		1	0.21		1
Social determinants
Maternal schooling
None/< 8 years	0.91	< 0.0001	1.58 (1.00;2.47	0.47	< 0.0001	2.30 (1.53;3.46)	0.42	0.0278	2.24 (0.62;8.02)
8–11 years	0.33	0.0378	0.88 (0.57;1.36)	0.24	< 0.0001	1.59 (1.07;2.35)	0.23	0.3293	1.39 (0.44;4.37)
≥ 12 years	0.22		1	0.10		1	0.14		1
Previous living children
1	0.43	0.0340	1.35 (0.96;1.90)	0.24	0.3070		0.25	0.2870
2	0.63	< 0.0001	1.63 (1.09;2.45)	0.31	0.0060	1.32 (0.96;1.81)	0.45	0.0240	2.69 (1.07;6.79)
≥ 3	1.30	< 0.0001	2.64 (1.82;3.81)	0.52	< 0.0001	1.65 (1.21;2.24)	0.34	0.1040	1.16 (0.41;3.31)
Nenhum	0.31		1	0.21		1	0.15
Previous deceased children
≥ 1	0.59	0.2986		0.33	0.1362	1.16 (0.84;1.59)	0.22	0.7627
None	0.49			0.26		1	0.26
Health care determinants
Prenatal visits
None	1.81	< 0.0001	2.90 (2.01;4.19)	1.17	< 0.0001	3.79 (2.70;5.33)	1.82	< 0.0001	6.97 (2.24;21.70)
1–3	1.03	< 0.0001	1.76 (1.26;2.45)	0.52	< 0.0001	1.81 (1.34;2.45)	0.54	0.0404	1.98 (0.61;6.44)
4–6	0.56	< 0.0001	1.19 (0.88;1.59)	0.35	< 0.0001	1.36 (1.07;1.73)	0.22	0.7916
≥ 7	0.30		1	0.19		1	0.20		1
Type of delivery
Cesarean	0.38	0.0004	0.96 (0.74;1.25)	0.24	0.0305	1.39 (1.13;1.70)	0.30	0.2895
Vaginal	0.58		1	0.29		1	0.21
Type of Hospital
Public	0.53	< 0.0001	1.30 (0.79;2.15)	0.31	< 0.0001	1.41 (0.93;2.13)	0.33	0.0932	1.16 (0.38;3.51)
Mixed	0.73	< 0.0001	1.69 (1.02;2.79)	0.35	< 0.0001	1.60 (1.05;2.43)	0.21	0.4613
Private	0.17		1	0.11		1	0.13		1

*Adjusted model to variables of the same stratum with P < 0.20 in the bivariate analysis. IR, incidence ratio; CI 95%, confidence interval of 95% no population