Table 1.

Summary of included studies.

References	Design type	Country	Birth year	Age of GA exposure	Number of GA exposure
Sprung et al. (11)	Retrospective cohort study	Rochester	1976–1982	Before age 2	0 (n = 4,156) 1 (n = 226) ≥2 (n = 43)
Ko et al. (10)	Retrospective matched-cohort study	Taiwan	2001–2005	Before age 3	0 (n = 13,172) 1 (n = 2,019) ≥2 (n = 1,274)
Hu et al. (9)	Retrospective cohort study	Olmsted County, Minnesota	1996–2000	Before age 3	0 (n = 463) 1 (n = 457) ≥2 (n = 116)
Tsai et al. (12)	Retrospective cohort study	Taiwan	1997–1999	Before age 3	0 (n = 3438) 1 (n = 804) ≥2 (n = 342)

GA, general anesthesia.