Prevalence and risk factors related to preterm birth in Brazil

Table 3 Maternal characteristics associated with spontaneous/pPROM preterm births

	Model A			Model B			Model C
	OR adj.^d (95 % CI)			OR adj.^e (95 % CI)			OR adj.^f (95 % CI)
Level 1 - Sociodemographic characteristics
Childbirth healthcare (ref: public)
Private	0.82	0.47	1.42
Age (ref: 20 to 34)
12 to 19	1.52*	1.29	1.80	1.41*	1.12	1.77	1.37	1.10	1.71
≥ 35	1.10	0.85	1.43	1.13	0.88	1.45	1.06	0.83	1.36
Skin color (ref: white)
Black	1.02	0.78	1.33
brown	1.03	0.81	1.33
Marital status (ref: live with partner)
Do not live with partner	0.93	0.77	1.12
Years of schooling (ref: ≥ 15)
≤ 7	1.49*	0.95	2.33	1.67*	1.16	2.42	1.73	1.16	2.57
8 to 10	1.31	0.83	2.06	1.45*	1.03	2.04	1.50	1.05	2.14
11 to 14	1.17	0.75	1.80	1.24	0.88	1.74	1.29	0.92	1.81
Level 2 - Obstetric history
Previous births (ref: 1 to 2) ^a
0				1.29*	1.06	1.57	1.37	1.15	1.65
≥ 3				1.25*	0.99	1.59	1.21	0.95	1.54
Previous abortion^b (ref: no, in women with a previous pregnancy)				0.99	0.80	1.23
Previous stillbirth or neonatal death^c (ref: no, in women with a previous delivery)				1.05	0.76	1.45
Previous preterm birth^c (ref: no, in women with a previous delivery)				3.42*	2.70	4.32	3.74	2.92	4.79
Previous caesarean section^c (ref: no, in women with a previous delivery)
1				0.59*	0.46	0.76	0.61	0.47	0.78
≥ 2				0.51*	0.35	0.74	0.47	0.31	0.71
Level 3 - Maternal/fetal conditions during pregnancy
Adequacy of antenatal care (ref: adequate)
Inadequate or partially adequate							1.29	1.09	1.52
Type of pregnancy (ref: single)
Multiple							16.42	10.56	25.53
Obstetric risk (ref: no)
Infection at hospital admission for birth							4.89	1.72	13.88
Abruptio placentae							2.38	1.27	4.47

^aSeparate models B and C, not including the other obstetric history variables, were performed to estimate the OR and 95 % CI for the variable “Previous births”
^bPrimigravida women were allocated in a separate category
^cNuliparous women were allocated in a separate category
^dadjusted for type of payment of birth, age, skin color, marital status and schooling
^eadjusted for age, schooling, previous births, previous abortion, previous stillbirth or neonatal death, previous preterm births and previous caesaren section
^fadjusted for age, schooling, previous births, previous preterm births, previous caesaren section, adequacy of antenatal care, type of pregnancy, infection at hospital admission for birth and abruptio placeantae
*P-value lower than 0.10

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