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Yoko Imaizumi and Kazuo Hayakawa
Objective: To compare the infant mortality rate (IMR) due to sudden infant death syndrome (SIDS) in twins and singletons and consider the risk factors of SIDS.
Materials and methods: The IMR due to SIDS was analyzed among twins and singletons from 1995 to 2008 using the Japanese Vital Statistics.
Results and discussion: The IMR for both twins and singletons decreased (1/3-1/4) significantly during 1995- 2008 and was significantly higher among twins than in singletons during 1995-2000 and 2003-2004. The relative risks of SIDS for maternal age groups between <25 years and 30–34 years were 9-fold for twins and 3-fold for singletons.
The IMR increased with parity for both 1st- and 2nd-twin born. Seasonal variations were observed in IMRs for twins and singletons. The time of death from 4 a.m. to 7 a.m. was a risk factor for SIDS in twins and singletons.
Conclusion: The relative risks for SIDS in twins and singletons decreased after 2005. The SIDS IMR was lower in Japan than in the US, the UK, and Canada which related to lower percentage of prone and facedown sleeps position in Japan. The concordance rate of SIDS was uncommon in twins. Younger maternal age is a risk factor for both twins and singletons.