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Abstract
Under the hygiene hypothesis, children born by cesarean section (CS) may consequently have an increased risk of asthma and other allergic diseases. CS has been shown to have a delayed and altered development in establishment of gut flora and altered cytokine production. Concerns about the relations between CS and the risk of children's asthma are rising due to the growing number of CS performed in many countries. However, finding the concrete evidence to correlate CS with higher risk of asthma is still controversial. There were significant covariate imbalance between groups of children born by CS vs. vaginal delivery that include the number of maternal age, gestational age, birth weight, complication during pregnancy, complication during labor, socioeconomic status, a parental history of atopy, and maternal smoking history. And there were considerable heterogeneity in methods and study subjects between the studies of delivery by CS and the offspring's risk of asthma and other allergic diseases. Therefore, as we proceed into the further study, researchers must refer to the literatures and look for the best way proving their hypothesis that are based on the methodological subject group. Of which should be accordance with the research purposes. Also, researchers have to search for identifying the core biological mechanism in order to know whether there is a causal relationship exists between the CS and asthma.
References
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Table 1.
Characteristics and Relative Risks of Selected Studies which Showed Cesarean Section is Associated with an Increased Risk for Asthma and Other Allergic Diseases46,47)
| First author, year (reference number) | Year of births | Country | Design | Exclusion∗ | Ascertainment method | Risk adjustment† | Asthma | Other allergic disease |
|---|---|---|---|---|---|---|---|---|
| Magnus,1)2011 | 1999–2008 | Norway | Cohort | No | Parental questionnaire | Basic+PaSmSe | 1.17 | |
| (diagnosis) | (1.03–1.32) | |||||||
| Tollånes,2)2008 | 1988–1998 | Norway | Cohort | No | Medical records (ICD code) | Basic+PaSe | 1.42 (1.25–1.61) P-CS | |
| 1.59 | ||||||||
| (1.44–1.75) E-CS | ||||||||
| Metsälä,38)2008 | 1996–2004 | Finland | Case-contro | ol No | Nationwide register | Basic+PaSm | 1.19 | |
| (medication) | (1.07–1.31) P-CS | |||||||
| 1.39 | ||||||||
| (1.27–1.58) E-CS | ||||||||
| van Beijsterveldt,39)200 | 8 1991–2000 | Nederland | Cohort | No | Questionnaire | Basic+Sm | 1.59 | |
| (diagnosis) | (1.23–2.06) 1st twin | |||||||
| 0.91 | ||||||||
| (0.69–1.19) 2nd twin | ||||||||
| Roduit,32)2009 | 1996–1997 | Nederland | Cohort | No | Parental questionnaire | Basic+PaSmSe | 1.79 | |
| (symptoms) | (1.27–2.51) | |||||||
| Renz-Polster,31)2005 | 1990–1992 | USA | Cohort | Yes | Health maintenance | Basic+SmSe | 1.24 | AR 1.37 |
| organization medical | (1.01–1.53) | (1.14–1.63) | ||||||
| records (diagnosis) | AD 0.9 | |||||||
| (0.70–1.16) | ||||||||
| FA 1.34 | ||||||||
| (0.54–3.29)‡ | ||||||||
| Salam,34)2006 | 1975–1987 | USA | Cohort | Yes | Parental questionnaire | Basic+PaSmSe | 1.33 | AR 1.57 |
| (diagnosis) | (1.01–1.75) | (1.24–1.99) | ||||||
| AD 1.07 | ||||||||
| (0.67–1.70) | ||||||||
| FA 1.18 | ||||||||
| (0.85–1.62) | ||||||||
| Negele,28)2004 | 1997–1999 | Europe | Cohort | Yes | Parental questionnaire (diagnosis) | PaSe | 1.41 (1.02–1.96) RW | AD 1.04 (0.79–1.39) |
| FA 1.64 | ||||||||
| (1.03–2.63) | ||||||||
| IA 1.75 | ||||||||
| (0.98–3.12) | ||||||||
| Vonk,40)2004 | 1975–1978 | Nederland | Cohort | No | Methacholine test | No | IA 0.75 | |
| (bronchial hyperactivity) | (0.39–1.44)§ | |||||||
| Xu,36)2001 | 1966 | Finland | Cohort | No | Questionnaire (diagnosis) | Basic+PaSmSe | 3.23 (1.53–6.80) | AR 1.28 (0.73–2.24) |
| AD 1.19 | ||||||||
| (0.62–2.28) | ||||||||
| FA 0.96 | ||||||||
| (0.59–1.56) | ||||||||
| Mckeever,24)2002 | 1988–1999 | UK | Cohort | No | Physician diagnosis | 1.09 | AR 1.01 | |
| (1.01–1.18) | (0.85–1.21) | |||||||
| AD 1.04 | ||||||||
| (0.98–1.10) | ||||||||
| Bager,14)2003 | 1973–1977 | Denmark | Cohort | No | Interview (diagnosis) | Basic | 1.31 (1.01–1.71) | AR 1.15 (0.90–1.48) |
| Gessner,17)2007 | 1990–2001 | USA | Cohort | No | Hospital clinic | No | 1.46 | |
| (ICD code) | (1.28–1.67)§ | |||||||
| 1.09 | ||||||||
| (1.00–1.18)§ | ||||||||
| Smith,43)2004 | 1992–95 | UK | Cohort | Yes | Hospital admissions | No | 1.17 | |
| (ICD code) | (1.02–1.57)§ | |||||||
| Debley,16)2005 | 1987–1994 | USA | Case-contro | ol No | Hospital admissions | Sm | 1.20 | |
| (ICD code) | (1.04–1.39) | |||||||
| Kero,21)2002 | 1987 | Finland | Cohort | No | 1) Hospital admissions an | nd Basic | 1.21 | |
| medications databases | s | (1.08–1.36) | ||||||
| (ICD code) | ||||||||
| 2) Clinical visit (diagnosis | s) | |||||||
| Håkansson,19)2003 | 1984–1996 | Sweden | Case-control | Yes | Hospital discharge records (ICD code) | Basic+SmSe | 1.35 (1.27–1.44) | |
| Annesi-Maesano,4)2001 | 1958 | UK | Cohort | No | Questionnaire | Basic+PaSm | 1.46 | |
| (symptoms) | (1.02–2.07)§ E-CS | |||||||
| Xu,37)2000 | 1985–1986 | Finland | Cohort | No | Parental questionnaire | Basic+Pa | 1.38 | |
| (diagnosis) | (1.00–1.92) |
FA, food allergy; IA, inhalant allergen sensitization; AD, eczema/atopic dermatitis; AR, allergic rhinitis; NS, not significant; E-CS, emergency cesarean section; P-CS, planned cesarean section.
† Basic: Maternal age, prematurity (gestational age or birth weight), parity and birth order. Pa, parental allergy; Sm, smoking in pregnancy or ETS perinatal period; Se, socioeconomic status (household income, parental education, or social
Table 2.
Characteristics and Relative Risks of Selected Studies which Showed Cesarean Section is Not Associated with an Increased Risk for Asthma and Other Allergic Diseases46,47)
| First author, year (reference number) | Year of births | Country | Design | Exclusion∗ | Ascertainment method | Risk adjustment† | Asthma | Other allergic disease |
|---|---|---|---|---|---|---|---|---|
| Menezes,25)2011 | 1993–2004 | Brazil | Cohort | No | Parental questionnaire (diagnosis) | Basic+PaSmSe | 1.16 (0.81–1.68) 1.18 (0.94–1.48) 1.02 (0.80–1.31) | |
| Rusconi,33)2007 | 1994–1995 | Italy | Cross-sectional | No | Parental questionnaire (symptoms) | Basic+PaSmSe | 0.97 (0.78–1.19) | |
| Maitra,23)2004 | 1991–1992 | UK | Cohort | No | Parental questionnaire (diagnosis) | Basic+PaSmSe | 1.14 (0.9–1.4) | IA 1.04 (0.8–1.3) |
| Sugiyama,35)2007 | 2002–2003 | Japan | Cohort | Yes | Physician diagnosis | No | AD 0.77 (0.22–2.73) | |
| Bernsen,41)2005 | 1988–1990 | Nederland | Cohort | No | Medical records (diagnosis) | Basic+PaSe | 1.03 (0.51–2.08) | AD 0.94 (0.26–3.33) |
| Nafstad,27)2000 | 1992–1993 | Norway | Cohort | Yes | Questionnaire (diagnosis and symptoms) | No | 1.1 (0.7–1.8) | AR 1.2 (0.7–2.1) |
| Montgomery,26)2000 | 1970 | UK | Cohort | No | Medical records (diagnosis) | Basic+PaSe | AR 1.21 (0.84–1.74) | |
| Calvani,15)2004 | 1991–98 | Italy | Case-control | No | Parental questionnaire (diagnosis) | No | 0.78 (0.58–1.06)‡ | |
| Juhn,20)2005 | 1976–1982 | USA | Cohort | No | Medical records (diagnosis or symptoms) | Se | 0.93 (0.6–1.4) | |
| Olivetti,29)1996 | 1983–1989 | USA | Case-control | No | Hospital clinic (diagnosis and medication) | No | 1.09 (0.62–1.91)‡ | |
| Werner,42)2007 | 1984–1987 | Denmark | Cohort | Yes | Parental questionnaire (diagnosis) | SmSe | 1.11 (0.88–1.39) | |
| Benn,44)2002 | 1992–1994 | Denmark | Cohort | No | Hospital clinic (medication) | Sm | 1.2 (0.3–4.3) | |
| Al-Kubaisy,13)2005 | 1988–1996 | Iraq | Case-control | No | Questionnaire (diagnosis and medication) | No | (0.3–4.3) 0.92 (0.64–1.34) | |
| Hagendorens,18)2005 | 1997–2001 | Nederland | Cohort | No | Parental questionnaire (symptoms) | PaSmSe | 1.31 (0.80–2.13) | |
| Park,30)2010 | Around 2003 | Korea | Cross-sectional | No | Medical records (diagnosis) | Basic+PaSm | 0.76 (0.37–1.57) | AR 1.14 (0.61–2.10) AD 1.01 (0.59–1.71) |
| Lee,45)2011 | Around 1997 | Korea | Cross-sectional | No | Parental questionnaire (diagnosis and symptoms) | Basic+PaSmSe | NS | AR NS AD NS |
| Kim,22)2011 | 1976–1979 | USA | Cohort | No | Medical records (diagnosis or symptoms) | Basic+PaSmSe | NS |
FA, food allergy; IA, inhalant allergen sensitization; AD, eczema/atopic dermatitis; AR, allergic rhinitis; NS, not significant; E-CS, emergency cesarean section; P-CS, planned cesarean section.
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