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Table 1 Characteristics of studies qualified for meta-analysis

From: The association between caesarean section and childhood asthma: an updated systematic review and meta-analysis

Authors, publication date, (reference)

Design

Country/continent

Age (years)

Asthma definition

Sample size

Year of birth

RRa (95% CIb)

Quality of studies

Xu et al. 2000 [21]

Cohort prospective

Finland/Europe

7

Parental questionnaire (diagnosis)

8088

1985–1986

1.38 (1.00–1.92)

High

Nafstad et al. 2000 [22]

Cohort prospective

Norway/Europe

4

Questionnaire (diagnosis and symptoms)

2531

1992–1993

1.10 (0.70–1.80)

High

Kero et al. 2002 [8]

Cohort retrospective

Finland/Europe

7

57 years: hospital admissions and medications databases (ICD code); at 7 years: clinical visit (diagnosis)

59,927

1987–1995

1.21 (1.08–1.36)

High

McKeever et al. 2002 [11]

Cohort retrospective

UK/Europe

0–11

Parental questionnaire (diagnosis)

29,238

1993–1997

1.09 (1.01–1.18)

High

Bager et al. 2003 [9]

Cohort prospective

Denmark/Europe

< 28

Interview (diagnosis

9722

1973–1977

1.33 (1.02–1.74)

High

Hakansson et al. 2003 [10]

Cohort retrospective

Sweden/Europe

> 1

Hospital discharge records (ICD code)

316,918

1984–1996

1. 14 (1.07–1.22)

High

Maitra et al. 2004 [12]

Cohort prospective

UK/Europe

5–8

Parental questionnaire (diagnosis)

12,367

1991–1992

1.16 (0.90–1.50)

High

Smith et al. 2004 [23]

Cohort retrospective

Scotland/Europe

8–9

Hospital admissions (ICD code)

241,846

1992–1995

1.10 (1.00–1.20)

High

Renz-polster et al. 2005 [24]

Cohort prospective

US/USA

3–10

Medical records (diagnosis)

8953

1990–1992

1.24 (1.01–1.57)

High

Bernsen et al. 2005 [25]

Cohort retrospective

Netherlands/Europe

> 6

Medical records (diagnosis)

1961

1988–1990

1.03 (0.51–2.08)

High

Juhn et al. 2005 [26]

Cohort retrospective

UK/Europe

7

Medical records (diagnosis or symptoms)

7106

1976–1982

0.93 (0.60–1.40)

High

Delbey et al. 2005 [27]

Case–control retrospective

Washington/USA

6–12

Hospital admissions (ICD code)

10,320

–

1.20 (1.04–1.39)

High

Salam et al. 2006 [28]

Cohort retrospective

US/USA

< 18

Parental questionnaire (diagnosis)

6259

1975–1987

1.33 (1.01–1.75)

High

Werner et al. 2007 [29]

Cohort prospective

Danish/Europe

15–18

Parental questionnaire (diagnosis)

7119

1984–1987

1.11 (0.88–1.39)

High

Roduit et al. 2008 [30]

Cohort prospective

Netherlands/Europe

8

Parental questionnaire (diagnosis)

2917

1996–1997

1.79 (1.27–2.51)

High

Pistiner et al. 2008 [31]

Cohort prospective

US/USA

9

Parental questionnaire (diagnosis)

432

1994–1996

1.10 (0.60–2.30)

Moderate

Tollnes et al. 2008 [32]

Cohort retrospective

Norway/Europe

18

Parental questionnaire (diagnosis)

1,869,380

1967–1998

1.52 (1.42–1.62)

High

Metsala et al. 2008 [33]

Cohort retrospective

Finland/Europe

> 3

Hospital admissions (ICD code)

22,548

1996–2004

1.15 (1.05–1.25)

High

Mohammadzadeh et al. 2009 [34]

Case–control retrospective

Iran/Asia

3–14

Hospital admissions (ICD code)

512

–

1.20 (0.80–1.70)

Moderate

Devidson et al. 2010 [35]

Cohort retrospective

UK/Europe

2–11

Hospital admissions (ICD code)

248,612

1970–1989

1.18 (1.02–1.34)

High

Park et al. 2010 [36]

Cohort retrospective

Korea/Asia

≤ 16

Questionnaire (diagnosis and Symptoms)

279

2003

0.76 (0.37–1.57)

Moderate

Nimwegen et al. 2011 [37]

Cohort prospective

Netherlands/Europe

6–7

Parental questionnaire (diagnosis)

2343

2002

0.89 (0.50–1.56)

High

Magnus et al. 2011 [38]

Cohort prospective

Norway/Europe

3

Parental questionnaire (diagnosis)

37,171

1999–2008

1.15 (1.02–1.29)

High

Nathan et al. 2011 [39]

Case–control retrospective

Malaysian/Asia

3–15

Hospital admissions (ICD code)

156

–

1.17 (0.47–2.91)

Moderate

Almqvist et al. 2012 [40]

Cohort retrospective

Sweden/Europe

> 10

National patient register (ICD code)

87,500

1993–1999

1.20 (1.05–1.37)

High

Hancox et al. 2012 [41]

Cohort retrospective

New Zealand/Oceania

13

Hospital admissions (ICD code)

1037

1972–1973

0.92 (0.32–2.65)

High

Kolokotroni et al. 2012 [42]

Cross-sectional

Cyprus/Europe

8

Parental questionnaire (diagnosis)

2216

–

1.41 (1.09–1.83)

High

Braback et al. 2013 [43]**

Cohort retrospective

Sweden/Europe

2–5

Swedish prescribed Drug Register (Antiasthmatic drugs)

199,837

1999–2006

1.20 (1.13–1.28)

High

Braback et al. 2013 [43]**

Cohort retrospective

Sweden/Europe

6–9

Swedish prescribed Drug Register (Antiasthmatic drugs)

199,837

1999–2006

1.18 (1.09–1.27)

High

Guibas et al. 2013 [44]

Cross-sectional

Aetoloakarnania/Europe

9–13

Hospital admissions (ICD code)

2572

–

1.39 (1.04–1.87)

High

Van Berkel et al. 2015 [51]

Cohort prospective

Netherlands/Europe

6

Questionnaire (diagnosis)

6128

–

1.09 (0.76–1.55)

High

Black et al. 2016 [45]

Cohort retrospective

UK, Scotland/Europe

5

Hospital admissions (ICD code)

40,145

1993–2007

1.11 (0.99–1.25)*

High

Kristensen et al. 2016 [52]

Cohort

Denmark/Europe

0–14

Hospital admissions (ICD code)

750,569

1997–2012

1.12 (1.09–1.50)

High

Sevelsted et al. 2016 [53]

Cohort prospective

Denmark/Europe

0–15

–

864,049

1997–2010

2.18 (1.27–3.73)

High

Lavin et al. 2017 [46]**

Cohort prospective

India/Asia

8

Questionnaire (diagnosis)

2026

2001–2002

2.60 (1.30–5.40)

High

Lavin et al. 2017 [46]**

Cohort prospective

Vietnam/Asia

8

Questionnaire (diagnosis)

2000

2001–2002

2 (1.20–3.30)

High

Chu et al. 2017 [54]

Case–control retrospective

China/Asia

4–12

Questionnaire (diagnosis)

1385

2015–2016

–

High

Brix et al. 2017 [47]

Cohort retrospective

Denmark/Europe

0–15

(ICD code)

928

1997–2012

–

High

Rusconi et al. 2017 [55]

Cohort retrospective

European/Europe

5–9

Questionnaire (diagnosis

67,613

1996–2006

1.22 (1.02–1.46)

High

  1. aRelative risk for overall cesarean section
  2. bConfidence interval
  3. * RR was calculated based on event and total numbers in case and control groups
  4. ** Some studies have been included and estimated the RR for more than one population or regions