The relationship between otitis media and intrauterine growth: a co-twin control study

The association between intrauterine growth, as measured by weight and gestational age, and the occurrence of recurrent ear infections was studied using data from a population-based sample of 7992 Norwegian twins. 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 otitis media (OM) were estimated Birth weight among individuals who reported OM was significantly lower than for controls, with a mean weight difference of 86 g. The average difference in gestational age was 3 days shorter among individuals with a positive history of OM. Next, the effect of birth weight was estimated using the co-twin control method. Among MZ twins, within-pair differences in birth weight reflect environmental 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. When within-pair birth weight differences were compared, the co-twin without a history of OM was used as the matched control. Results indicated that lower birth weight may be a risk factor for OM. The average birth weight difference among OM-discordant pairs was 48 g, with the control twin weighing significantly more than the twin with a history of OM.