Table 5.

Summary of the Results of Previous Studies of Birth by Cesarean Section and Atopy or Atopic Diseases

Reference (Number)	Study Design	Duration of Follow-up(f/u)	Sample size at f/u baseline	Odds ratio (95% CI) for the association between cesarean delivery and
				Asthma	Hay fever or allergic rhinitis	Sensitization to ≥1 allergens
Kero et al (7)	Retrospective/Database (DB)	7 yrs	59,927	1.2 (1.1–1.4)	N/A	1.3 (0.7–2.7)*
Salam et al (8)	Retrospective	8 to 17 yrs	2,928/6,259	1.3 (1.0–1.8)	1.6 (1.2–2.0)	N/A
McKeever et al (15)	Retrospective/DB	0 to 11 yrs	24,690/29,238	1.1 (1.0–1.1)	1.0 (0.9–1.2)	N/A
Xu et al (9)	Prospective&	31 yrs	1,953/11,635	3.2 (1.5–6.8)	1.3 (0.7–2.2)	1.0 (0.6–1.6)
Nafstad et al (17)	Prospective	4 yrs	2,531/3,754	1.1 (0.7–1.8)	1.2 (0.7–2.1)	N/A
Annesi-Maesano et al+ (16)	Retrospective	1 to 18 yrs	4,065/4,153	1.2 (0.7–2.0)	N/A	N/A
Maitra et al^ (14)	Prospective	7 yrs	7,495/14,062	1.2 (0.9–1.5)	N/A	1.1 (0.9–1.5)
Renz-Polster et al (10)	Retrospective/DB	3–10 yrs	7,872/8,953	1.2 (1.0–1.5)	1.4 (1.1–1.6)	N/A
Negele K et al (11)	Prospective	2 yrs	2,500/3,097	N/A	1.4 (0.8–2.4)	1.7 (1.0–2.9)
Bager et al (12)	Retrospective/DB	20–28 yrs	9,722/10,482	1.3 (1.0–1.7)	1.2 (0.9–1.5)	N/A
Eggesbo et al (33)	Prospective	2 yrs	2,803/3,621	N/A	N/A	3.2 (1.4–7.3).
Hakansson et al (13)	Retrospective case-control/DB	1 yr	650,959/916,131	1.1 (1.1–1.2)***	N/A	N/A

^*Of the 59,927 members of the birth registry, 131 underwent allergy skin testing

^&1,953 of 11,635 subjects in the birth cohort were included in the study. Obstetric data was obtained in all non-normal births but in only 10% of reportedly normal births.

⁺Only emergency cesarean sections were included.

^{^}5,916 of the 14,062 participants underwent allergy skin testing.

^***Asthma was defined as at least one hospitalization for asthma.

N/A=Not available.