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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