Table 2.

Crude percentage of birth defects in ART pregnancy according to plurality.

Year	Singletons	Multiples	RR (95% CI)	Total
2004	0.43 (88/20,304)	0.97 (35/3,612)	2.24 (1.51–3.30)	0.50 (123/23,916)
2005	0.53 (119/22,524)	0.92 (35/3,784)	1.75 (1.20–2.55)	0.59 (154/26,308)
2006	0.67 (165/24,787)	1.52 (52/3,424)	2.28 (1.67–3.11)	0.77 (218/28,211)
2007	0.93 (240/25,944)	1.92 (62/3,221)	2.08 (1.58–2.74)	1.04 (304/29,165)
2008	1.06 (322/30,372)	2.10 (45/2,139)	1.98 (1.46–2.70)	1.13 (368/32,511)
Total	0.75 (934/123,931)	1.42 (229/16,180)	1.88 (1.60–2.13)	0.83 (1,167/140,111)a

Numbers of ART pregnancies according to plurality were presented in the JSOG annual report.

^aTotal number includes four subjects with unknown plurality.