THE RELATIONSHIP BETWEEN OTITIS-MEDIA AND INTRAUTERINE GROWTH - A COTWIN CONTROL STUDY

The association between intrauterine growth: as measured by weight and gestational age, and the occurrence of recurrent ear infections was s tudied using data from a population-based sample of 7992 Norwegian twi ns. Perinatal measures were collected from the Medical Birth Registry, and reports of recurrent ear infections were based on questionnaires completed when the twins were aged 18-25 years. First, the individual effects of birth weight and gestational age on the occurrence of otiti s media (OM) were estimated. Birth weight among individuals who report ed OM was significantly lower than for controls, with a mean weight di fference of 86 g. The average difference in gestational age was 3 days shorter among individuals with a positive history of OM. Next, the ef fect of birth weight was estimated using the co-twin control method. A mong MZ twins, within-pair differences in birth weight reflect environ mental differences experienced in utero. Among DZ pairs, birth weight differences may be due to genetic and environmental differences. Among OM-discordant pairs, the co-twin without a history of OM is a matched control for comparisons of intra-pair differences in birth weight. Wh en within-pair birth weight differences were compared, the co-twin wit hout a history of OM was used as the matched control. Results indicate d that lower birth weight may be a risk factor for OM. The average bir th weight difference among OM-discordant pairs was 48 g, with the cont rol twin weighing significantly more than the twin with a history of O M.