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July 1999

Sudden Infant Death Syndrome Among Twins

Author Affiliations

From the Department of Pediatrics (Dr Malloy) and the Office of Biostatistics (Dr Freeman), The University of Texas Medical Branch, Galveston.

Arch Pediatr Adolesc Med. 1999;153(7):736-740. doi:10.1001/archpedi.153.7.736

Background  Sudden infant death syndrome (SIDS) is a major contributor to infant mortality. Previous studies have suggested that infants born of twin pregnancies are at greater risk for SIDS and that a twin who survives after a co-twin dies is at increased risk for SIDS.

Objective  To attempt to confirm the increased risk of SIDS among and within twin pairs through the use of US vital statistics data.

Methods  We analyzed data from the US-linked birth and infant death certificate tapes for the years 1987 through 1991 to determine the risk of SIDS in twin births compared with singleton births and to describe the characteristics of twin pairs in whom SIDS occurred. The analysis was limited to live births with weights of 500 g or more and gestational ages of 24 weeks or more. We used an algorithm to match co-twins (infants within a twin pair) to measure sex and birth weight concordancy; to identify twin pairs, in which one or both twins died of SIDS; and to examine, when both twins died, whether they died on the same day.

Results  There were 23,464 singleton SIDS deaths and 1056 twin SIDS deaths during the 5-year period. The crude relative risk for SIDS among twins compared with singleton births was 2.06 (95% confidence interval, 1.94-2.19). The adjusted relative risk independent of birth weight and sociodemographic variables was 1.13 (95% confidence interval, 0.97-1.31). We successfully matched the co-twins of 172,029 twin pregnancies. Of these, 767 were twin pregnancies in which one or both twins died of SIDS. Among the 767 twin pregnancies in which one or both twins experienced SIDS, there were only 7 in which both twins died of SIDS (rate ratio, 4.0 per 100,000 twin pregnancies). In only 1 of these 7 did both twins die on the same day (rate ratio, 0.58 per 100,000 twin pregnancies). The relative risk for a second twin dying of SIDS was 8.17 (90% confidence interval, 1.18-56.67).

Conclusions  Independent of birth weight, twins do not appear to be at greater risk for SIDS compared with singleton births. In addition, the occurrence of both twins dying of SIDS is uncommon, and the occurrence of both twins dying on the same day is extremely uncommon.