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Table 3 Maternal characteristics associated with spontaneous/pPROM preterm births

From: Prevalence and risk factors related to preterm birth in Brazil

  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 abortionb (ref: no, in women with a previous pregnancy)     0.99 0.80 1.23    
 Previous stillbirth or neonatal deathc (ref: no, in women with a previous delivery)     1.05 0.76 1.45    
 Previous preterm birthc (ref: no, in women with a previous delivery)     3.42* 2.70 4.32 3.74 2.92 4.79
 Previous caesarean sectionc (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
  1. 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”
  2. bPrimigravida women were allocated in a separate category
  3. cNuliparous women were allocated in a separate category
  4. dadjusted for type of payment of birth, age, skin color, marital status and schooling
  5. eadjusted for age, schooling, previous births, previous abortion, previous stillbirth or neonatal death, previous preterm births and previous caesaren section
  6. 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
  7. *P-value lower than 0.10