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

AIMS/HYPOTHESIS: We investigated whether children who are heavier at birth have an increased risk of type 1 diabetes. METHODS: Relevant studies published before February 2009 were identified from literature searches using MEDLINE, Web of Science and EMBASE. Authors of all studies containing relevant data were contacted and asked to provide individual patient data or conduct pre-specified analyses. Risk estimates of type 1 diabetes by category of birthweight were calculated for each study, before and after adjustment for potential confounders.Meta-analysis techniques were then used to derive combined ORs and investigate heterogeneity between studies. RESULTS: Data were available for 29 predominantly European studies (five cohort, 24 case-control studies), including 12,807 cases of type 1 diabetes. Overall, studies consistently demonstrated that children with birthweight from 3.5 to 4 kg had an increased risk of diabetes of 6% (OR 1.06 [95% CI 1.01-1.11]; p=0.02) and children with birthweight over 4 kg had an increased risk of 10% (OR 1.10 [95% CI 1.04-1.19]; p=0.003), compared with children weighing 3.0 to 3.5 kg at birth. This corresponded to a linear increase in diabetes risk of 3% per 500 g increase in birthweight (OR 1.03 [95% CI 1.00-1.06]; p=0.03). Adjustments for potential confounders such as gestational age, maternal age, birth order, Caesarean section, breastfeeding and maternal diabetes had little effect on these findings. CONCLUSIONS/INTERPRETATION: Children who are heavier at birth have a significant and consistent, but relatively small increase in risk of type 1 diabetes.

Comparison of the incidence of insulin-dependent diabetes mellitus in childhood among five Baltic populations during 1983-1988.

We have carried out a comparison of the incidence of childhood onset insulin-dependent diabetes mellitus (IDDM) between five populations around the Baltic Sea. These were Finland, Estonia, Latvia, Lithuania and Poland. The risk of IDDM is highest in the world in Finland and also very high in Sweden, on the western and northern side of the Baltic Sea. The risk of IDDM in children on the eastern side of the Baltic Sea has not been known before. The data collection period covered the years 1983-1988. A marked variation in incidence was seen within this relatively small geographical area. Among these five populations, the incidence increased with the latitude. Our present results confirmed the very high incidence of IDDM in Finland. The average age-standardized yearly incidence of IDDM/100,000 was in males under 15 years of age 36.9 in Finland, 10.7 in Estonia, 6.4 in Latvia, 6.5 in Lithuania and 6.0 in Poland. In females the incidence was 31.6, 10.0, 6.9, 7.0 and 6.4 in these five populations, respectively. The differential in incidence in Estonia as compared with Latvia, Lithuania and Poland was statistically significant (P = 0.0002). A slight male excess in incidence was found in countries with higher incidence--Finland and Estonia, but in lower incidence countries the sex ratio was opposite (P = 0.019 for the interaction sex-population). During 1983-1988 the incidence increased significantly in Finland but not in other populations although a large year-to-year variation in incidence was observed in each country, particularly in males. We recorded a peak in IDDM incidence in most of these populations around 1986.

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

AIMS/HYPOTHESIS: The aim of this study was to investigate the evidence of an increased risk of childhood-onset type 1 diabetes in children born by Caesarean section by systematically reviewing the published literature and performing a meta-analysis with adjustment for recognised confounders. METHODS: After MEDLINE, Web of Science and EMBASE searches, crude ORs and 95% CIs for type 1 diabetes in children born by Caesarean section were calculated from the data reported in each study. Authors were contacted to facilitate adjustments for potential confounders, either by supplying raw data or calculating adjusted estimates. Meta-analysis techniques were then used to derive combined ORs and to investigate heterogeneity between studies. RESULTS: Twenty studies were identified. Overall, there was a significant increase in the risk of type 1 diabetes in children born by Caesarean section (OR 1.23, 95% CI 1.15-1.32, p < 0.001). There was little evidence of heterogeneity between studies (p = 0.54). Seventeen authors provided raw data or adjusted estimates to facilitate adjustments for potential confounders. In these studies, there was evidence of an increase in diabetes risk with greater birthweight, shorter gestation and greater maternal age. The increased risk of type 1 diabetes after Caesarean section was little altered after adjustment for gestational age, birth weight, maternal age, birth order, breast-feeding and maternal diabetes (adjusted OR 1.19, 95% CI 1.04-1.36, p = 0.01). CONCLUSIONS/INTERPRETATION: This analysis demonstrates a 20% increase in the risk of childhood-onset type 1 diabetes after Caesarean section delivery that cannot be explained by known confounders.

Increasing incidence of childhood-onset type I diabetes in 3 Baltic countries and Finland 1983-1998.

AIMS/HYPOTHESIS: We aimed to study the incidence of Type I diabetes in 4 countries, Estonia, Latvia, Lithuania and Finland, during 1983-1998, focusing on the two separate periods of 1983-1990 and 1991-1998. METHODS: Population-based incidence data from nationwide diabetes registries were used. Crude and age-standardized incidence rates using the proportions of 39%, 32% and 29% for 5-year age groups (0-4, 5-9 and 10-14 years) were calculated. Yearly incidence was evaluated and the means between the two periods compared. RESULTS: Between 1983-1990 and 1991-1998 there was a statistically significant incidence increase in all 4 countries of Estonia, Lativia, Lithuania and Finland (relative risk 1.15, 95%-Confidence interval 1.10-1.19) and as well as in the 3 Baltic states of Estonia, Latvia, Lithuania (relative risk 1.13, 95%. Confidence interval 1.04-1.22). The crude incidence increased in Estonia from 10.1 (95%-Confidence interval 8.9-11.4) to 12.3 (11.0-13.8), in Latvia from 6.6 (5.8-7.3) to 7.4 (6.6-8.2) and in Lithuania from 6.8 (6.2-7.5) to 7.8 (7.1-8.5). In Finland the incidence rose from 34.6 (33.3-36.0) in 1983-1990 to 40.8 (39.4-42.2) in 1991-1998. In children under 5 years of a age a statistically important increase was seen in Estonia and Finland. The highest incidence for a single year was recorded for all participating countries in the late 1990 s. The highest annual incidence rate of childhood onset Type I diabetes in the world ever known was recorded in Finland in 1998 with 48.5 cases per 100 000 person-years. CONCLUSION/HYPOTHESIS: The incidence of Type I diabetes has increased since 1983 in the three Baltic states as well as in Finland. Long-term monitoring is needed for a better detection in changes in incidence.

Incidence trends in childhood onset IDDM in four countries around the Baltic sea during 1983-1992.

We present secular trends of childhood onset insulin-dependent diabetes mellitus (IDDM) in Finland, Estonia, Latvia and Lithuania during the period of 1983-1992. Incidence data were obtained from the national IDDM registries. The average age-standardized incidence per 100,000/year was 35.0 in Finland, followed by 10.2 in Estonia, 7.1 in Lithuania and 6.5 in Latvia. A male excess in incidence was recorded in Finland (1.15) and Latvia (1.01). In all countries, the highest age-specific risk of IDDM was observed in the 11-13 year age range. The large difference in incidence between Finland and other Baltic countries was see even in 1-2 year-old children. During the 10-year study period overall changes in incidence of IDDM were relatively small in these four countries. The incidence increased in Finland and Lithuania on average by 1% and 1.4% per year, respectively. A statistically significant increase was recorded only in 0-4 year old children in Finland, at 5.6% per year. In Estonia, an 8.3% increase in this age group, however, was not statistically significant. The different trends in the age-group specific incidence rates were confirmed in Finland. In conclusion, from 1983 to 1992 the incidence of childhood onset IDDM was increasingly in Finland and Lithuania, while in Latvia and Estonia it was stable. There are still great differences in IDDM incidence between the countries around the Baltic Sea.

Seasonal variation in the incidence of Type 1 diabetes mellitus during 1983 to 1992 in the countries around the Baltic Sea.

AIM: To examine seasonal patterns of incidence of Type 1 diabetes mellitus incidence in children aged 0-14 years in Finland, Sweden, Estonia, Latvia and Lithuania during 1983-1992 (1987-1992 for Finland). METHODS: The study used a method that models incidence data using combinations of sine waves to model seasonal variation around a possible linear trend. RESULTS: In Finland, a significant pattern was found for combined sexes and age groups 0-9 and 10-14 years. A significant pattern was also confirmed for 10-14 year-old boys. In Sweden, the best model with significant pattern was found separately for boys and girls and age groups 0-9 and 10-14 years, however, a significant pattern was confirmed for older girls only. A seasonal pattern in older boys in Finland and girls in Sweden was characterized by two cycles with decreased incidence in June and November-December. The pattern among younger children (0-9 or 5-9 years) had one cycle with a decreased incidence in May-June. In Estonia, a significant pattern was found for the age group 0-14 years and combined sexes. No significant seasonal patterns were found in Latvia and Lithuania. CONCLUSIONS: The seasonal pattern with two cycles among older children and one cycle only among younger children may indicate different triggers of Type 1 diabetes mellitus for different age groups.