Table 4. Difference in means for the characteristics used in weighting women, according to the type of recurrent prematurity. Brazil, 2011–2012.

	Recurrent spontaneous preterm birth		Recurrent provider-initiated preterm birth
	Before balancing	After balancing	Before balancing	After balancing
Maternal age
12 to 19 years	0.034	-0.026	0.034	-0.026
20 to 34 years	-0.021	0.009	-0.021	0.009
≥ 35 years	-0.000	0.026	-0.000	0.026
Socioeconomic status
Class D/E - low	0.044	0.050	0.044	0.050
Class C - middle	-0.018	-0.049	-0.018	-0.049
Class A/B - high	-0.025	0.004	-0.025	0.004
Smoking in the third trimester of pregnancy
No	-0.015	0.035	-	-
Yes, < 10 cigarettes/day	0.042	-0.027	-	-
Yes, ≥ 10 cigarettes/day	-0.031	-0.021	-	-
Parity
1–2 previous deliveries	-0.222	-0.056	-0.222	-0.056
≥ 3 previous deliveries	0.222	0.056	0.222	0.056
Previous cesarean section
Yes	-	-	0.089	-0.018
No	-	-	-0.089	0.018
Previous stillbirth or neonatal death
Yes	0.422	-0.035	0.422	-0.035
No	-0.422	0.035	-0.422	0.035
Chronic hypertension
Yes	0.099	0.002	0.099	0.002
No	-0.099	-0.002	-0.099	-0.002
Chronic Diabetes
Yes	0.005	-0.003	0.005	-0.003
No	-0.005	0.003	-0.005	0.003