Seasonality of births and childhood inflammatory bowel disease

Abstract

Purpose: In some geographical areas, including Slovakia, children with diabetes mellitus type 1 are born more often in summer than in late autumn and winter. Does this also apply to another autoimmune disorder - inflammatory bowel disease - in Slovakia? Basic procedures: The month of birth was recorded for 30 boys and 36 girls with Crohn disease and 23 boys and 40 girls with ulcerative colitis. The monthly numbers of births were adapted to the length of the given month, divided by the number of boys or girls born in the whole Slovak children's population in the same calendar month in comparable years, transformed to moving averages from three successive values each, and expressed as the fraction of the yearly total, which was equal to 1. According to the null hypothesis, there should be equal probability (1/12) of being born in any month. The significance of departures from this value was evaluated with cosinor regression using two sinusoidal functions with period lengths of 12 and 6 months. The most illustrative measure is the relation of the corridor of 95% confidence for the total approximating function to the midline estimating statistic of rhythm (the mesor) (1/12). Significant departures up or down are recognized as nonoverlapping of the mesor straight line by the confidence corridor. Main findings: These were similar to those reported for childhood diabetes mellitus type 1. In our sample of Crohn disease, the number of births was markedly higher between June and October and lower between December and March. In ulcerative colitis, there was a slight increase between June and August and a decrease between December and February. Principal conclusions: The seasonal effect on births of children with later childhood-onset Crohn disease is similar to that described for diabetes mellitus type 1, i. e. maximal frequency of births in summer. © Springer-Verlag 2005.