Fetal growth retardation in sudden infant death syndrome (SIDS) babies and their siblings

To evaluate the intrauterine growth potential of infants that die from sudden infant death syndrome (SIDS), the authors compared SIDS infants with their surviving siblings. The SIDS sibships themselves were also compared with sibships where all infants survived. Data from the population-based Medical Birth Registry of Norway, with 1.3 million births during 1967-1988, were used. From the birth cohorts, 1,984 SIDS cases were identified. All births were linked into sibships. The mean birth weight and gestational age were calculated across sibships of different sizes for first to fourth birth order. In a further analysis, birth weights were standardized to adjust for gestational age. Mothers of SIDS infants give birth to smaller babies in general. SIDS infants weighed, on average, 85 g less at birth than their siblings and 164 g less compared with babies in nonaffected sibships. When birth weights were standardized for gestational age, most of the weight difference between SIDS infants and siblings was due to a shorter gestational age of SIDS infants, while the difference between surviving siblings of SIDS infants and births from nonaffected sibships remained. All births in sibships with a SIDS infant were intrauterine growth retarded. This may reflect factors that contribute to SIDS risk (such as maternal smoking). The factors that contribute to shorter gestational age and further slowing of growth in the SIDS infants may specifically influence the SIDS infant and not its siblings.