Characteristic Twins Singletons OR [95%CI] Twins vs. Singletons Deaths IMR3) OR [95%CI] Deaths IMR3) OR [95%CI] Maternal age1), y               ＜25 26 1.30 8.76 [4.57–16.78] 601 0.38 2.97 [2.64–3.35] 3.43 [2.31, 5.07] 25–29 37 0.55 3.71 [2.00–6.86] 614 0.16 1.26 [1.12–1.41] 3.42 [2.45, 4.76] 30–34 14 0.15 1.00 Reference 504 0.13 1.00 Reference 1.16 [0.68, 2.17] ≥35 8 0.16 1.09 [0.46–2.59] 240 0.15 1.15 [0.98–1.34] 1.10 [0.55, 2.23] Birthweight2), g               ＜1500 32 1.37 4.59 [2.78–7.59] 103 1.23 6.12 [5.03–7.45] 1.11 [0.75, 1.65] 1500–2499 91 0.47 1.58 [1.04–2.40] 524 0.48 2.38 [2.17–2.61] 0.99 [0.79, 1.23] ≥ 2500 29 0.30 1.00 Reference 2935 0.20 1.00 Reference 1.48 [1.03, 2.14] Gestational age1), w               <32 17 1.08 3.85 [2.20–6.76] 68 1.09 7.17 [5.62–9.13] 0.99 [0.58, 1.69] 32–34 15 0.59 2.09 [1.16–3.75] 57 0.63 4.13 [3.17–5.39] 0.93 [0.53, 1.64] 35–37 43 0.28 2.09 [1.16–3.75] 362 0.28 1.82 [1.62–2.04] 1.01 [0.74, 1.39] ≥ 38 11 0.30 1.07 [0.55–2.08] 1457 0.15 1.00 Reference 1.97 [1.09, 3.57] Sex combination of twins2)               Like-sex 974) 0.43 1.27 [0.84–1.91]         Unlike-sex 30 0.34 1.00 Reference         Total 1525) 0.49           Note: 1)Reported period, 1999-2008; 2)Reported period, 1995-2008; 3)IMR per 1000 live births; 4)Including one case of SIDS-SIDS; 5)Including unknown sex of co-twin

Table 2: Infant mortality rate due to SIDS of selected characteristics for twins and singletons.