Table 1 Severe maternal morbidity incidence using four indicators and the study populations’ characteristics (2003–2018)

Maternal age (y)

 15–19

23,179

96.4

862

3.6

 < .0001

22,944

95.4

1,097

4.6

 < .0001

23,983

99.8

58

0.2

 < .0001

23,664

98.4

377

1.6

 < .0001

 20–24

313,014

97.8

6,999

2.2

310,163

96.9

9,850

3.1

319,343

99.8

670

0.2

316,158

98.8

3,855

1.2

 25–29

1,757,569

98.1

34,153

1.9

1,743,220

97.3

48,502

2.7

1,787,457

99.8

4,265

0.2

1,771,009

98.8

20,713

1.2

 30–34

2,921,132

97.8

65,872

2.2

2,899,720

97.1

87,284

2.9

2,978,744

99.7

8,260

0.3

2,948,384

98.7

38,620

1.3

 35–39

1,100,678

96.9

35,550

3.1

1,092,320

96.1

43,908

3.9

1,130,918

99.5

5,310

0.5

1,116,714

98.3

19,514

1.7

 40–44

148,938

95.1

7,703

4.9

147,636

94.3

9,005

5.8

155,204

99.1

1,437

0.9

152,476

97.3

4,165

2.7

 45 + 

5,048

92.8

394

7.2

4,998

91.8

444

8.2

5,358

98.5

84

1.5

5,234

96.2

208

3.8

Household income

 1Q (Low)

1,257,640

97.5

32,705

2.5

 < .0001

1,247,497

96.7

42,848

3.3

 < .0001

1,285,885

99.7

4,460

0.4

 < .0001

1,271,599

98.6

18,746

1.5

 < .0001

 2Q

1,590,797

97.7

38,155

2.3

1,578,391

96.9

50,561

3.1

1,623,749

99.7

5,203

0.3

1,606,787

98.6

22,165

1.4

 3Q

2,211,770

97.7

51,557

2.3

2,194,855

97

68,472

3

2,256,625

99.7

6,702

0.3

2,233,451

98.7

29,876

1.3

 4Q (High)

1,209,351

97.7

29,116

2.4

1,200,258

96.9

38,209

3.1

1,234,748

99.7

3,719

0.3

1,221,802

98.7

16,665

1.4

Type of health insurance

 Self-employed

1,689,352

97.3

46,924

2.7

 < .0001

1,675,974

96.5

60,302

3.5

 < .0001

1,729,256

99.6

7,020

0.4

 < .0001

1,710,475

98.5

25,801

1.5

 < .0001

 Employee

4,546,866

97.8

102,663

2.2

4,512,048

97

137,481

3

4,636,691

99.7

12,838

0.3

4,588,734

98.7

60,795

1.3

 Medical aid

33,340

94.5

1,946

5.5

32,979

93.5

2,307

6.5

35,060

99.4

226

0.6

34,430

97.6

856

2.4

Residential area

 Seoul

1,281,035

97.7

29,985

2.3

 < .0001

1,271,383

97

39,637

3

 < .0001

1,307,052

99.7

3,968

0.3

 < .0001

1,295,457

98.8

15,563

1.2

 < .0001

 Metropolitan region

1,544,941

97.6

37,502

2.4

1,533,021

96.9

49,422

3.1

1,576,887

99.7

5,556

0.4

1,557,354

98.4

25,089

1.6

 Small cities

3,027,116

97.7

72,423

2.3

3,003,602

96.9

95,937

3.1

3,090,716

99.7

8,823

0.3

3,059,769

98.7

39,770

1.3

 Rural

416,466

97.3

11,623

2.7

412,995

96.5

15,094

3.5

426,352

99.6

1,737

0.4

421,059

98.4

7,030

1.6

Mode of delivery

 Vaginal delivery

2,170,826

98.8

27,032

1.2

 < .0001

2,155,660

98.1

42,198

1.9

 < .0001

2,194,396

99.8

3,462

0.2

 < .0001

2,177,073

99.1

20,785

1

 < .0001

 Instrument delivery

1,750,562

98

35,350

2

1,736,117

97.2

49,795

2.8

1,782,129

99.8

3,783

0.2

1,758,974

98.5

26,938

1.5

 Cesarean section

2,348,170

96.3

89,151

3.7

2,329,224

95.6

108,097

4.4

2,424,482

99.5

12,839

0.5

2,397,592

98.4

39,729

1.6

Preterm birth

 No

6,139,508

97.8

138,641

2.2

 < .0001

6,092,686

97.1

185,463

3

 < .0001

6,259,755

99.7

18,394

0.3

 < .0001

6,196,081

98.7

82,068

1.3

 < .0001

 Yes

130,050

91

12,892

9

128,315

89.8

14,627

10.2

141,252

98.8

1,690

1.2

137,558

96.2

5,384

3.8

Parity

 0

3,248,026

97.4

86,637

2.6

 < .0001

3,219,016

96.5

115,647

3.5

 < .0001

3,323,886

99.7

10,777

0.3

 < .0001

3,283,131

98.5

51,532

1.6

 < .0001

 1 + 

3,021,532

97.9

64,896

2.1

3,001,985

97.3

84,443

2.7

3,077,121

99.7

9,307

0.3

3,050,508

98.8

35,920

1.2

Multiple birth

 No

6,186,857

97.8

141,715

2.2

 < .0001

6,139,428

97

189,144

3

 < .0001

6,309,615

99.7

18,957

0.3

 < .0001

6,244,363

98.7

84,209

1.3

 < .0001

 Yes

82,701

89.4

9,818

10.6

81,573

88.2

10,946

11.8

91,392

98.8

1,127

1.2

89,276

96.5

3,243

3.5

Prenatal care^*

 Adequate

5,309,789

97.8

122,423

2.3

 < .0001

5,267,814

97

164,398

3

 < .0001

5,416,867

99.7

15,345

0.3

 < .0001

5,358,203

98.6

74,009

1.4

 < .0001

 Intermediate

871,738

97.1

25,838

2.9

865,763

96.5

31,813

3.5

893,375

99.5

4,201

0.5

885,419

98.7

12,157

1.4

 Inadequate

57,314

96.6

2,006

3.4

56,861

95.9

2,459

4.2

58,990

99.4

330

0.6

58,436

98.5

884

1.5

 Missing

31,983

31,983

31,983

31,983

Maternal comorbidities^†

 0

3,908,136

98.2

73,223

1.8

 < .0001

3,880,064

97.5

101,295

2.5

 < .0001

3,972,890

99.8

8,469

0.2

 < .0001

3,935,912

98.9

45,447

1.1

 < .0001

 1 + 

2,361,422

96.8

78,310

3.2

2,340,937

96

98,795

4.1

2,428,117

99.5

11,615

0.5

2,397,727

98.3

42,005

1.7

Type of hospital

 ≥ 500 beds

341,950

89.8

38,680

10.2

 < .0001

337,394

88.6

43,236

11.4

 < .0001

376,134

98.8

4,496

1.2

 < .0001

366,186

96.2

14,444

3.8

 < .0001

 100–499 beds

669,389

95.2

33,786

4.8

661,773

94.1

41,402

5.9

697,438

99.2

5,737

0.8

690,670

98.2

12,505

1.8

 30–99 beds

2,513,725

98.5

37,579

1.5

2,496,628

97.9

54,676

2.1

2,545,664

99.8

5,640

0.2

2,518,029

98.7

33,275

1.3

 < 30 beds

2,744,494

98.5

41,488

1.5

2,725,206

97.8

60,776

2.2

2,781,771

99.9

4,211

0.2

2,758,754

99

27,228

1

Region of hospital

 Seoul

1,294,441

97.3

35,505

2.7

 < .0001

1,284,473

96.6

45,473

3.4

 < .0001

1,325,181

99.6

4,765

0.4

 < .0001

1,312,693

98.7

17,253

1.3

 < .0001

 Metropolitans

1,747,196

97.5

45,328

2.5

1,733,515

96.7

59,009

3.3

1,785,397

99.6

7,127

0.4

1,761,969

98.3

30,555

1.7

 Small cities

3,174,813

97.9

69,582

2.1

3,150,354

97.1

94,041

2.9

3,236,279

99.8

8,116

0.3

3,205,299

98.8

39,096

1.2

 Rural

53,108

97.9

1,118

2.1

52,659

97.1

1,567

2.9

54,150

99.9

76

0.1

53,678

99

548

1

Total

6,269,558

97.6

151,533

2.4

6,221,001

96.9

200,090

3.1

6,401,007

99.7

20,084

0.3

6,333,639

98.6

87,452

1.4