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Table 3 The relationship between risk factors and the four indicators of severe maternal morbidity

From: Comparison of global indicators for severe maternal morbidity among South Korean women who delivered from 2003 to 2018: a population-based retrospective cohort study

  US-CDC’s SMM P-value Gold standard guideline for SMM P-value Zwart’s SMM P-value EURONET-SAMM P-value
RR 95% CI RR 95% CI RR 95% CI RR 95% CI
Individual factors
 Maternal age (y)
  15–19 1.35 1.25 1.45  < .0001 1.27 1.19 1.36  < .0001 0.85 0.64 1.13 0.277 1.05 0.95 1.17 0.3392
  20–24 1.09 1.06 1.12  < .0001 1.09 1.06 1.11  < .0001 0.88 0.81 0.95 0.0024 0.98 0.95 1.02 0.2914
  25–29 1.00     1.00     1.00     1.00    
  30–34 1.10 1.08 1.11  < .0001 1.05 1.04 1.07  < .0001 1.17 1.12 1.21  < .0001 1.14 1.12 1.16  < .0001
  35–39 1.34 1.32 1.36  < .0001 1.24 1.23 1.26  < .0001 1.76 1.69 1.84  < .0001 1.47 1.44 1.50  < .0001
  40–44 1.67 1.63 1.71  < .0001 1.52 1.49 1.56  < .0001 2.72 2.55 2.90  < .0001 2.04 1.97 2.11  < .0001
  ≥ 45 1.85 1.67 2.04  < .0001 1.70 1.54 1.87  < .0001 3.19 2.56 3.97  < .0001 2.49 2.17 2.86  < .0001
 Household Income level
  1Q (Low) 1.17 1.15 1.19  < .0001 1.14 1.12 1.16  < .0001 1.30 1.24 1.36  < .0001 1.13 1.10 1.15  < .0001
  2Q 1.14 1.13 1.16  < .0001 1.12 1.10 1.13  < .0001 1.24 1.18 1.29  < .0001 1.09 1.07 1.12  < .0001
  3Q 1.07 1.06 1.09  < .0001 1.06 1.05 1.08  < .0001 1.11 1.07 1.16  < .0001 1.04 1.02 1.06  < .0001
  4Q (High) 1.00     1.00     1.00     1.00    
 Type of health insurance
  Self-employed 1.14 1.13 1.16  < .0001 1.12 1.11 1.13  < .0001 1.21 1.17 1.25  < .0001 1.14 1.12 1.15  < .0001
  Employees 1.00     1.00     1.00     1.00    
  Medical aid 1.80 1.71 1.89  < .0001 1.70 1.63 1.78  < .0001 1.58 1.37 1.81  < .0001 1.57 1.46 1.68  < .0001
 Residential areas
  Seoul 1.00     1.00     1.00     1.00    
  Metropolitans 1.05 1.03 1.08  < .0001 1.04 1.01 1.06 0.001 1.00 0.93 1.06 0.9168 1.05 1.02 1.08 0.0038
  Small cities 1.15 1.13 1.18  < .0001 1.12 1.10 1.14  < .0001 1.22 1.15 1.28  < .0001 1.15 1.12 1.18  < .0001
  Rural 1.21 1.18 1.24  < .0001 1.17 1.14 1.20  < .0001 1.49 1.39 1.60  < .0001 1.39 1.34 1.44  < .0001
Obstetric factors
 Mode of delivery
  Vaginal delivery 1.00     1.00     1.00     1.00    
  Instrument delivery 1.53 1.51 1.56  < .0001 1.38 1.36 1.40  < .0001 1.37 1.30 1.43  < .0001 1.49 1.46 1.52  < .0001
  Cesarean section 2.28 2.25 2.32  < .0001 1.84 1.82 1.86  < .0001 2.51 2.41 2.61  < .0001 1.41 1.39 1.44  < .0001
 Preterm birth
  No 1.00     1.00     1.00     1.00    
  Yes 1.39 1.36 1.42  < .0001 1.36 1.34 1.39  < .0001 1.61 1.53 1.70  < .0001 1.53 1.49 1.58  < .0001
 Parity
  0 1.25 1.24 1.27  < .0001 1.27 1.26 1.28  < .0001 1.15 1.12 1.19  < .0001 1.39 1.37 1.41  < .0001
  1 +  1.00     1.00     1.00     1.00    
 Multiple birth
  No 1.00     1.00     1.00     1.00    
  Yes 1.64 1.60 1.67  < .0001 1.59 1.56 1.62  < .0001 1.37 1.29 1.46  < .0001 1.37 1.32 1.42  < .0001
 Prenatal care*
  Adequate 1.00     1.00     1.00     1.00    
  Intermediate 1.13 1.12 1.15  < .0001 1.05 1.04 1.06  < .0001 1.10 1.06 1.14  < .0001 0.97 0.95 0.99 0.0032
  Inadequate 1.39 1.33 1.45  < .0001 1.26 1.21 1.31  < .0001 1.38 1.23 1.54  < .0001 1.10 1.03 1.17 0.0066
 Maternal comorbidities
  0 1.00     1.00     1.00     1.00    
  ≥ 1 1.51 1.50 1.53  < .0001 1.42 1.41 1.43  < .0001 2.32 2.25 2.39  < .0001 1.33 1.31 1.35  < .0001
Provision factors
 Type of hospital
  ≥ 500 beds 5.54 5.45 5.62  < .0001 4.47 4.40 4.53  < .0001 3.29 3.15 3.44  < .0001 2.53 2.48 2.59  < .0001
  100–499 beds 2.94 2.89 2.99  < .0001 2.54 2.50 2.57  < .0001 2.61 2.50 2.71  < .0001 1.35 1.32 1.38  < .0001
  30–99 beds 1.00     1.00     1.00     1.00    
  < 30 beds 1.04 1.03 1.06  < .0001 1.04 1.03 1.06  < .0001 0.69 0.66 0.72  < .0001 0.81 0.80 0.83  < .0001
 Region of hospital
  Seoul 1.00     1.00     1.00     1.00    
  Metropolitan 1.35 1.32 1.38  < .0001 1.32 1.30 1.35  < .0001 1.60 1.51 1.69  < .0001 1.52 1.47 1.57  < .0001
  Small cities 1.23 1.21 1.25  < .0001 1.22 1.20 1.24  < .0001 1.02 0.97 1.07 0.4545 1.12 1.09 1.15  < .0001
  Rural 1.17 1.10 1.24 < 0.0001 1.19 1.13 1.26  < .0001 0.47 0.38 0.60  < .0001 0.92 0.84 1.01 0.0704
  1. Adjusted for maternal age, household income level, type of health insurance, residential area, mode of delivery, preterm birth, parity, multiple birth, prenatal care, maternal comorbidities, type of hospital, region of hospital, and year
  2. EURONET-SAMM European Network on Severe Acute Maternal Morbidity, US-CDC United States Centers for Disease Control and Prevention, CI confidence interval, GSG gold standard guidelines, RR relative risk, SMM severe maternal morbidity
  3. *Prenatal care is estimated using Kessner’s adequate prenatal care index
  4. Maternal comorbidities included are: cardiac disease, renal disease, musculoskeletal disease, digestive disorder, blood disease, mental disorders, CNS disease, rheumatic heart disease, placentation disorder, chronic hypertension, pregnancy hypertension, lupus, collagen vascular disorder, rheumatoid arthritis, diabetes, diabetes complicating pregnancy, obesity, and asthma/chronic bronchitis