A Case-Control Investigation of Perinatal Risk Factors for Childhood IDDM in Northern Ireland and Scotland

Abstract

Many reported risk factors are weak and show inconsistencies between studies. They may be secondary to more direct, as-yet-undiscovered risk factors. Although irrelevant in the majority of cases, the increased risk associated with delivery by cesarean section deserves further study.

Caesarean section is associated with an increased risk of childhood-onset type 1 diabetes mellitus: a meta-analysis of observational studies

“…Gestational diabetes is another possibility, but the proportion of mothers with gestational diabetes in these European populations is likely to be small [47], reducing the likelihood of marked confounding, and adjustment for gestational diabetes in seven of the studies [15,25,27] revealed little evidence of confounding. A further weakness of this study was that the reason for Caesarean section could not be investigated, as this was not available in the majority of studies, and therefore we were unable to confirm a report suggesting that any increased risk of type 1 diabetes after Caesarean section was most marked after elective procedures [24].…”

“…The searches identified nine eligible articles using MEDLINE [15,17,[24][25][26][27][28][29][30]; a further article was identified from Web of Science [31] and another from EMBASE [32]. The more general MEDLINE search identified a further eight articles [33][34][35][36][37][38][39][40], and review of reference lists revealed another two articles [41,42].…”

“…The 16 remaining articles corresponded to 20 independent studies, because one study [15] provided data from eight centres, three of which were reported elsewhere [25,27,32], and another provided data from two centres [24], one of which was subsequently reported in a larger study [32]. Finally, to ensure two studies [17,30] provided independent information, authors removed cases from one study [30] that were included in the other [17].…”

“…However, as this meta-analysis was based upon observational studies, it is impossible to rule out the influence of unrecorded confounders, although any such confounder would have to operate similarly across all studies. Social class is a possibility, as it may be associated with the likelihood of delivery by Caesarean section, but as the association between social class and type 1 diabetes is inconsistent [24,[44][45][46] it seems unlikely that it could exert the necessary confounding influence. Gestational diabetes is another possibility, but the proportion of mothers with gestational diabetes in these European populations is likely to be small [47], reducing the likelihood of marked confounding, and adjustment for gestational diabetes in seven of the studies [15,25,27] revealed little evidence of confounding.…”

Birthweight and the risk of childhood-onset type 1 diabetes: a meta-analysis of observational studies using individual patient data

“…The findings of this research seem inconsistent, as some studies have concluded that high birthweight is associated with increased diabetes risk [8] or reduced diabetes risk [9], while others have shown no association with type 1 diabetes risk [10]. Interpretation of these findings is made more difficult because studies have reported associations using many different categorisations of birthweight [8,[11][12][13][14], with some [15,16] only reporting findings for the extremes of birthweight and others [17][18][19][20][21] not reporting their birthweight results in any detail, concentrating instead on other findings. This could lead to reporting bias if the decision to report birthweight findings was influenced by whether or not results were interesting or 'statistically significant'.…”