the study was performed in children from the babydiab study , a longitudinal study examining the natural history of islet autoimmunity and type 1 diabetes in 1,650 children born to a mother or father with type 1 diabetes ( 10 ) . venous blood samples were obtained from children at study visits scheduled at 9 months and at 2 , 5 , 8 , 11 , 14 , 17 , and 20 years of age . autoantibodies against insulin ( iaas ) , gad ( gadas ) , insulinoma antigen 2 ( ia-2as ) , and zinc transporter 8 ( znt8as ) were measured in samples taken at all scheduled visits and every 6 months in children with islet autoantibodies . the median follow - up time from birth to last sample was 11.0 years ( interquartile range 8.012.5 ) and from birth to last contact was 13.9 years ( 11.915.6 ) . the babydiab study was approved by the ethical committee of bavaria , germany ( bayerische landesrztekammer number 95357 ) . investigations were carried out in accordance with the principles of the declaration of helsinki , as revised in 2000 . iaas , gadas , ia-2as , and znt8as were determined centrally by the institute of diabetes research munich using radiobinding assays as previously described ( 10,11 ) . briefly , iaas were measured by protein a / g radiobinding assays using [ i]-recombinant human insulin labeled at tyrosine amino acid 14 , and gadas , ia-2as , and znt8as were measured separately by protein a radiobinding assays using [ s]-methionine  labeled in vitro transcribed / translated recombinant human gad65 , intracellular portion of ia-2 , and the cooh - terminal portion of znt8 for the two major variants at amino acid 325 , respectively . offspring were considered positive for islet autoantibodies when two consecutive samples collected after birth were positive . islet autoantibody assays were evaluated by the diabetes autoantibody standardization program ( laboratory 121 ) ( 12,13 ) . relevant to the current study , this included maternal age at delivery , gestational age , mode of delivery , sex of the child , and singleton birth status . where no pediatric record was provided , the mode of delivery was recorded as missing . parity status and smoking behavior during pregnancy were self - reported in a questionnaire completed by the mothers before or at delivery . hla - drb1 , hla - dqa1 , and hla - dqb1 alleles were typed using pcr - amplified dna and nonradioactive sequence - specific oligonucleotide probes as described previously ( 14 ) . classification into high - risk hla genotypes was based on the environmental determinants of diabetes in the young ( teddy ) study inclusion genotypes for first - degree relatives ( 15 ) : dr4-dqa1 * 030x - dqb1 * 0302/dr3-dqa1 * 0501-dqb1 * 0201 ; dr4-dqa1 * 030x - dqb1 * 0302/dr4-dqa1 * 030x - dqb1 * 0302 ; dr4-dqa1 * 030x - dqb1 * 0302/dr8- dqa1 * 0401-dqb1 * 0402 , dr3-dqa1 * 0501-dqb1 * 0201/dr3-dqa1 * 0501-dqb1 * 0201 ; dr4-dqa1 * 030x - dqb1 * 0302/dr4-dqa1 * 030x - dqb1 * 020x ; dr4-dqa1 * 030x - dqb1 * 0302/dr1-dqa1 * 0101-dqb1 * 0501 ; dr4-dqa1 * 030x - dqb1 * 0302/dr13-dqa1 * 0102-dqb1 * 0604 , dr4-dqa1 * 030x - dqb1 * 0302/dr4-dqa1 * 030x - dqb1 * 0304 , dr4-dqa1 * 030-dqb1 * 0302/dr9-dqa1 * 030x - dqb1 * 0303 ; dr3-dqa1 * 0501-dqb1 * 0201/dr9-dqa1 * 030x - dqb1 * 0303 ; where   includes dqb1 * 0302 and dqb1 * 0304 . interferon - induced with helicase c domain ( ifih1 ) , cd25 , and ptpn22 genotypes were determined in 1,289 , 1,283 , and 1,295 children , respectively . the remaining children were not typed because of unsuitable or missing dna samples or unsuccessful typing . single - nucleotide polymorphism ( snp ) genotyping was performed with the massarray system using iplex chemistry ( sequenom , san diego , ca ) , as previously described ( 16 ) . reproducibility was assessed by duplicate genotyping in 16.3% of samples ( discordance rate , < 0.5% ) . for each of the snp typings , deviation from hardy - weinberg equilibrium time to event analyses ( kaplan - meier and cox proportional hazards model ) were used for diabetes and islet autoantibody outcomes . kaplan - meier analysis was used to calculate risk and to compare probabilities of type 1 diabetes and islet autoantibodies in children stratified for delivery mode and stratified for delivery mode and genotype . the cox proportional hazards model was used to determine hazard ratios ( hrs ) for multiple covariates . to identify potential confounders associated with cesarean section ( table 1 ) , variables that were associated with cesarean section were subsequently included as covariates in the cox proportional hazards model . for the cox model , these covariates were categorized as yes / no ( maternal diabetes , singleton birth , firstborn child , premature birth , breastfeeding <3 months , and hla teddy risk genotype ) or above and below median ( birth weight ) . for ifih1 , cd25 , and ptpn22 snps , children were categorized as either homozygous for the common allele or other , corresponding to a recessive susceptible model for ifih1 and cd25 and a dominant / codominant model for ptpn22 . for analyses with type 1 diabetes as the outcome , the age at diagnosis of diabetes or the age at last follow - up was used as the event time . for analyses with islet autoantibody status as the outcome , the age at the first sample positive for one or more islet autoantibodies was used as the event time . analyses were censored for loss to follow - up and for antibody - negative status at the subject s last autoantibody - negative sample according to age . the log - rank test was used to compare categories in the kaplan - meier analysis . as a test for homogeneity for findings with respect to cesarean section , a stratified analysis was performed after dividing the cohort into children born in the months january , march , may , july , september , or november ( odd months ) and children born in the months february , april , june , august , october , or december ( even months ) . a permutation analysis ( n = 100 ) was performed for the cox proportional hazards model that included cesarean section and the type 1 diabetes susceptibility genes . evidence for interaction between cesarean section and type 1 diabetes susceptibility genes associated with type 1 diabetes in the cohort was investigated by 1 ) adding the term cesarean sectiongenotype as a covariate in the cox proportional hazards model ; 2 ) cox proportional hazards model testing of cesarean section association with diabetes conditioned by a gene snp genotype categorized as either homozygous for the common allele or other ; and 3 ) kaplan - meier analysis after stratification for genotype as either homozygous for the common allele or other . where indicated , p values have been corrected using bonferroni correction , which was by a factor of 8 for covariates shown in table 1 and by a factor of 5 for kaplan - meier analyses with gene stratification in fig . all statistical analyses were performed using the statistical package for social science ( spss 18.0 ; chicago , il ) . the study was performed in children from the babydiab study , a longitudinal study examining the natural history of islet autoimmunity and type 1 diabetes in 1,650 children born to a mother or father with type 1 diabetes ( 10 ) . venous blood samples were obtained from children at study visits scheduled at 9 months and at 2 , 5 , 8 , 11 , 14 , 17 , and 20 years of age . autoantibodies against insulin ( iaas ) , gad ( gadas ) , insulinoma antigen 2 ( ia-2as ) , and zinc transporter 8 ( znt8as ) were measured in samples taken at all scheduled visits and every 6 months in children with islet autoantibodies . the median follow - up time from birth to last sample was 11.0 years ( interquartile range 8.012.5 ) and from birth to last contact was 13.9 years ( 11.915.6 ) . the babydiab study was approved by the ethical committee of bavaria , germany ( bayerische landesrztekammer number 95357 ) . investigations were carried out in accordance with the principles of the declaration of helsinki , as revised in 2000 . iaas , gadas , ia-2as , and znt8as were determined centrally by the institute of diabetes research munich using radiobinding assays as previously described ( 10,11 ) . briefly , iaas were measured by protein a / g radiobinding assays using [ i]-recombinant human insulin labeled at tyrosine amino acid 14 , and gadas , ia-2as , and znt8as were measured separately by protein a radiobinding assays using [ s]-methionine  labeled in vitro transcribed / translated recombinant human gad65 , intracellular portion of ia-2 , and the cooh - terminal portion of znt8 for the two major variants at amino acid 325 , respectively . offspring were considered positive for islet autoantibodies when two consecutive samples collected after birth were positive . islet autoantibody assays were evaluated by the diabetes autoantibody standardization program ( laboratory 121 ) ( 12,13 ) . relevant to the current study , this included maternal age at delivery , gestational age , mode of delivery , sex of the child , and singleton birth status . where no pediatric record was provided , the mode of delivery was recorded as missing . parity status and smoking behavior during pregnancy were self - reported in a questionnaire completed by the mothers before or at delivery . hla - drb1 , hla - dqa1 , and hla - dqb1 alleles were typed using pcr - amplified dna and nonradioactive sequence - specific oligonucleotide probes as described previously ( 14 ) . classification into high - risk hla genotypes was based on the environmental determinants of diabetes in the young ( teddy ) study inclusion genotypes for first - degree relatives ( 15 ) : dr4-dqa1 * 030x - dqb1 * 0302/dr3-dqa1 * 0501-dqb1 * 0201 ; dr4-dqa1 * 030x - dqb1 * 0302/dr4-dqa1 * 030x - dqb1 * 0302 ; dr4-dqa1 * 030x - dqb1 * 0302/dr8- dqa1 * 0401-dqb1 * 0402 , dr3-dqa1 * 0501-dqb1 * 0201/dr3-dqa1 * 0501-dqb1 * 0201 ; dr4-dqa1 * 030x - dqb1 * 0302/dr4-dqa1 * 030x - dqb1 * 020x ; dr4-dqa1 * 030x - dqb1 * 0302/dr1-dqa1 * 0101-dqb1 * 0501 ; dr4-dqa1 * 030x - dqb1 * 0302/dr13-dqa1 * 0102-dqb1 * 0604 , dr4-dqa1 * 030x - dqb1 * 0302/dr4-dqa1 * 030x - dqb1 * 0304 , dr4-dqa1 * 030-dqb1 * 0302/dr9-dqa1 * 030x - dqb1 * 0303 ; dr3-dqa1 * 0501-dqb1 * 0201/dr9-dqa1 * 030x - dqb1 * 0303 ; where   includes dqb1 * 0302 and dqb1 * 0304 . interferon - induced with helicase c domain ( ifih1 ) , cd25 , and ptpn22 genotypes were determined in 1,289 , 1,283 , and 1,295 children , respectively . the remaining children were not typed because of unsuitable or missing dna samples or unsuccessful typing . single - nucleotide polymorphism ( snp ) genotyping was performed with the massarray system using iplex chemistry ( sequenom , san diego , ca ) , as previously described ( 16 ) . reproducibility was assessed by duplicate genotyping in 16.3% of samples ( discordance rate , < 0.5% ) . for each of the snp typings , deviation from hardy - weinberg equilibrium was previously tested in a case - control set of samples . time to event analyses ( kaplan - meier and cox proportional hazards model ) were used for diabetes and islet autoantibody outcomes . kaplan - meier analysis was used to calculate risk and to compare probabilities of type 1 diabetes and islet autoantibodies in children stratified for delivery mode and stratified for delivery mode and genotype . the cox proportional hazards model was used to determine hazard ratios ( hrs ) for multiple covariates . to identify potential confounders associated with cesarean section ( table 1 ) , variables that were associated with cesarean section were subsequently included as covariates in the cox proportional hazards model . for the cox model , these covariates were categorized as yes / no ( maternal diabetes , singleton birth , firstborn child , premature birth , breastfeeding <3 months , and hla teddy risk genotype ) or above and below median ( birth weight ) . for ifih1 , cd25 , and ptpn22 snps , children were categorized as either homozygous for the common allele or other , corresponding to a recessive susceptible model for ifih1 and cd25 and a dominant / codominant model for ptpn22 . for analyses with type 1 diabetes as the outcome , the age at diagnosis of diabetes or the age at last follow - up was used as the event time . for analyses with islet autoantibody status as the outcome , the age at the first sample positive for one or more islet autoantibodies was used as the event time . analyses were censored for loss to follow - up and for antibody - negative status at the subject s last autoantibody - negative sample according to age . the log - rank test was used to compare categories in the kaplan - meier analysis . as a test for homogeneity for findings with respect to cesarean section , a stratified analysis was performed after dividing the cohort into children born in the months january , march , may , july , september , or november ( odd months ) and children born in the months february , april , june , august , october , or december ( even months ) . a permutation analysis ( n = 100 ) was performed for the cox proportional hazards model that included cesarean section and the type 1 diabetes susceptibility genes . association of cesarean section with pregnancy and birth factors * bonferroni - corrected values . evidence for interaction between cesarean section and type 1 diabetes susceptibility genes associated with type 1 diabetes in the cohort was investigated by 1 ) adding the term cesarean sectiongenotype as a covariate in the cox proportional hazards model ; 2 ) cox proportional hazards model testing of cesarean section association with diabetes conditioned by a gene snp genotype categorized as either homozygous for the common allele or other ; and 3 ) kaplan - meier analysis after stratification for genotype as either homozygous for the common allele or other . where indicated , p values have been corrected using bonferroni correction , which was by a factor of 8 for covariates shown in table 1 and by a factor of 5 for kaplan - meier analyses with gene stratification in fig . all statistical analyses were performed using the statistical package for social science ( spss 18.0 ; chicago , il ) . of the 1,505 children with delivery mode data , 560 were born by cesarean section and 945 by vaginal delivery ( fig . 1 ) . delivery by cesarean section was more frequent in children who were born to mothers with type 1 diabetes ( 47% ) than in children of nondiabetic mothers ( 22% ; pcorrected < 0.0001 ) , in nonsingleton births ( 62% ; pcorrected = 0.016 ) , in births at < 37 weeks of gestation ( 64% ; pcorrected < 0.0001 ) , in firstborn children ( 42% ; pcorrected < 0.0001 ) , and in children with birth weight less than the cohort median ( 40% , pcorrected = 0.048 ) , but was not associated with maternal age at delivery or maternal smoking during pregnancy ( table 1 ) . children who were delivered by cesarean section were breastfed less than children from vaginal delivery ( pcorrected < 0.001 ) . schematic diagram shows study participants , mode of delivery , and outcome with respect to islet autoantibodies and type 1 diabetes . * the five cases of diabetes that occurred in children without islet autoantibodies were not tested for islet autoantibodies for 9 , 7.7 , 6.8 , 4 , and 1.2 years before diabetes onset , respectively . the risk for developing type 1 diabetes by age 12 years was higher in children who were delivered by cesarean section ( 4.8% ; 95% ci 3.06.6% ) than children born by vaginal delivery ( 2.2% ; 1.23.2 ; p = 0.002 ; fig . 2a ) . the increased risk for diabetes among children delivered by cesarean section remained after adjusting for maternal diabetes , nonsingleton birth , premature delivery , firstborn children , and smoking during pregnancy ( adjusted hr 2.8;1.55.1 ; p = 0.001 ; table 2 ) . this increased risk was also observed when the analysis was limited to children of fathers with type 1 diabetes and nondiabetic mothers ( adjusted hr 4.7 ; 1.812.1 ; p = 0.001 ; n = 630 ) or when the cohort was stratified according to month of birth as a check for data homogeneity ( adjusted hr 2.5 , p = 0.048 for odd months ; adjusted hr 3.4 , p = 0.003 for even months ) . kaplan - meier analysis for the probability of developing type 1 diabetes ( a ) and islet autoantibodies ( b ) and for the progression to overt diabetes from first appearance of islet antibodies ( c ) in children delivered by cesarean section ( solid line ) or vaginally ( dashed line ) . numbers under the abscissa are the number of children still followed at each time point . p values are derived from log - rank tests comparing children delivered by cesarean section with children born by vaginal delivery . multivariate cox proportional hazards model for developing type 1 diabetes * bonferroni - corrected p = 0.007 . not applicable , since there were no diabetes cases in the 37 nonsingleton birth children . islet autoantibodies precede the development of type 1 diabetes and were identified in multiple samples from 147 of the babydiab children . however , there was no increase in the risk of islet autoantibodies in children who were delivered by cesarean section ( 13.8% ; 95% ci 9.917.7% ) compared with children with vaginal delivery ( 13% ; 1016% ; p = 0.6 ; fig . no differences between cesarean section and vaginal delivery were also observed for the probability of developing autoantibodies associated with thyroid autoimmunity and celiac disease ( supplementary fig . 2c , the rate of progression from the development of islet autoantibodies to overt type 1 diabetes in autoantibody - positive children was higher in children delivered by cesarean section ( 57% within 10 years ; 4173% ) versus children born by vaginal delivery ( 28% ; 1739% ; p = 0.015 ) . this remained significant after adjustment for potential confounding variables associated with cesarean section ( adjusted hr 2.4 ; 1.24.4 ; p = 0.008 ) . cesarean delivery is reported to be accompanied by a change in the infant s microbial and viral environment and immune response ( 5 ) . in addition to hla class ii genes ( 17 ) , the viral immune response  associated gene ifih1 is associated with type 1 diabetes development in our cohort ( 9 ) , and the cd25 gene and ptpn22 gene affect both immune response and type 1 diabetes risk ( 7 ) . we therefore examined genotypes of these four gene regions for association with type 1 diabetes and for possible interactions with cesarean section in the association with type 1 diabetes risk . with respect to association , a multivariate cox proportional hazards model showed that hla dr / dq genotype ( adjusted hr 7.3 ; 95% ci 4.013.4 ; p < 0.0001 ) , ifih1 genotype ( 2.4 ; 1.34.5 ; p = 0.005 ) , and cesarean section ( 2.7 ; 1.54.9 ; p = 0.001 ) contributed to the probability of developing type 1 diabetes in the babydiab cohort ( fig . permutation analysis in the multivariate cox model confirmed that hla dr / dq genotype ( p < 0.01 ) , ifih1 genotype ( p < 0.01 ) , and cesarean section ( p < 0.01 ) were associated with type 1 diabetes risk and further suggested an association with cd25 genotype ( p = 0.04 ) , but not ptpn22 genotype ( p = 0.49 ) , in the cohort . type 1 diabetes outcome and risk according to delivery mode and type 1 diabetes susceptibility genes . type 1 diabetes outcome stratified for delivery mode or the type 1 diabetes susceptibility genes is shown in the left - hand column . delivery mode is categorized as cesarean section or vaginal delivery , hla is categorized as teddy - defined risk genotypes or other , and snp genotype is categorized as homogeneous for the common allele versus other . * the reference group used to calculate adjusted hrs in the cox proportional hazards model is indicated for each covariate ( ref ) . the adjusted hrs ( large dots ) and 95% cis ( error bars ) for type 1 diabetes in the multivariate cox proportional hazards model are shown in the diagram . the model also included potential confounder variables associated with cesarean section in the babydiab study ( table 1 ) . the p values are obtained from the multivariate cox proportional hazards model . to search for potential interaction between cesarean section and susceptibility genes in influencing type 1 diabetes risk , we first added the interaction item cesarean sectiongenotype for each of the genes in the cox proportional hazards model . hrs for the interaction item were suggestive of interaction for ifih1 ( adjusted hr 2.3 ; p = 0.18 ) and for cd25 ( 0.2 ; p = 0.04 ) , but not for hla ( 0.96 ; p = 0.9 ) , prompting further analysis . we then examined type 1 diabetes risk associated with cesarean section conditioned by the genotypes of each of these three gene regions ( fig . 4 ) . adjusted hrs for cesarean section were similar for both hla risk and nonrisk genotypes , again suggesting that there was no interaction between cesarean section and hla genotype . in contrast , there were pronounced differences in adjusted hrs of cesarean section between children with risk and nonrisk genotypes at the ifih1 and cd25 genes , again suggesting interaction . interactions between cesarean section and type 1 diabetes susceptibility genes . a : adjusted hrs ( large dots ) for cesarean section versus vaginal delivery as a risk for type 1 diabetes are shown after stratification for genotype at hla , ifih1 , and cd25 genes . for the ifih1 and cd25 snps , the risk genotype used was the homozygous common allele , which is consistent with a recessive susceptibility model . b and c : kaplan - meier survival curves for type 1 diabetes risk according to delivery mode stratified for ifih1 ( b ) and cd25 ( c ) genotype . type 1 diabetes development curves for cesarean section and vaginal delivery are shown as thick and thin lines , respectively , and the color codes represent children with the type 1 diabetes susceptible ( blue ) and nonsusceptible ( green ) genotypes , as predicted by recessive susceptibility models . numbers under the abscissa are the number of children still followed at each time point . p values for comparisons are provided in the text . finally , we performed kaplan - meier analyses after stratification for ifih1 and cd25 genotypes . for the ifih1 genotypes examined , the increased risk associated with cesarean section was only evident in children who had both the diabetes - susceptible ifih1 gg genotype and cesarean section . the probability of type 1 diabetes by age 12 years in children with the ifih1 gg genotype was 9.1% ( 95% ci 4.913.3 ) in individuals delivered by cesarean section versus 2.8% ( 0.94.7 ) in individuals delivered vaginally ( pcorrected = 0.014 ) . in comparison , the probability for developing type 1 diabetes in children with the ga or aa ifih1 genotypes was 2.8% ( 0.84.8 ) if delivered by cesarean section and 1.7% ( 0.52.9 ; pcorrected = 0.9 ) if delivered vaginally . for cd25 , cesarean section was associated with increased risk for type 1 diabetes , regardless of cd25 genotype . however , there was a markedly reduced 12-year risk for type 1 diabetes in children who had nonsusceptible genotypes and vaginal delivery ( 0.6% ; 0.11.4 ) compared with all other groups : nonsusceptible genotypes and cesarean section , 5.7% ( 2.58.9 ; pcorrected = 0.0005 ) ; susceptible genotypes and vaginal delivery , 3.2% ( 1.64.8 ; pcorrected = 0.04 ) ; and susceptible genotypes and cesarean section , 5.9% ( 3.18.7% ; pcorrected = 0.0007 ) . of the 1,505 children with delivery mode data , 560 were born by cesarean section and 945 by vaginal delivery ( fig . 1 ) . delivery by cesarean section was more frequent in children who were born to mothers with type 1 diabetes ( 47% ) than in children of nondiabetic mothers ( 22% ; pcorrected < 0.0001 ) , in nonsingleton births ( 62% ; pcorrected = 0.016 ) , in births at < 37 weeks of gestation ( 64% ; pcorrected < 0.0001 ) , in firstborn children ( 42% ; pcorrected < 0.0001 ) , and in children with birth weight less than the cohort median ( 40% , pcorrected = 0.048 ) , but was not associated with maternal age at delivery or maternal smoking during pregnancy ( table 1 ) . children who were delivered by cesarean section were breastfed less than children from vaginal delivery ( pcorrected < 0.001 ) . schematic diagram shows study participants , mode of delivery , and outcome with respect to islet autoantibodies and type 1 diabetes . * the five cases of diabetes that occurred in children without islet autoantibodies were not tested for islet autoantibodies for 9 , 7.7 , 6.8 , 4 , and 1.2 years before diabetes onset , respectively . the risk for developing type 1 diabetes by age 12 years was higher in children who were delivered by cesarean section ( 4.8% ; 95% ci 3.06.6% ) than children born by vaginal delivery ( 2.2% ; 1.23.2 ; p = 0.002 ; fig . 2a ) . the increased risk for diabetes among children delivered by cesarean section remained after adjusting for maternal diabetes , nonsingleton birth , premature delivery , firstborn children , and smoking during pregnancy ( adjusted hr 2.8;1.55.1 ; p = 0.001 ; table 2 ) . this increased risk was also observed when the analysis was limited to children of fathers with type 1 diabetes and nondiabetic mothers ( adjusted hr 4.7 ; 1.812.1 ; p = 0.001 ; n = 630 ) or when the cohort was stratified according to month of birth as a check for data homogeneity ( adjusted hr 2.5 , p = 0.048 for odd months ; adjusted hr 3.4 , p = 0.003 for even months ) . kaplan - meier analysis for the probability of developing type 1 diabetes ( a ) and islet autoantibodies ( b ) and for the progression to overt diabetes from first appearance of islet antibodies ( c ) in children delivered by cesarean section ( solid line ) or vaginally ( dashed line ) . numbers under the abscissa are the number of children still followed at each time point . p values are derived from log - rank tests comparing children delivered by cesarean section with children born by vaginal delivery . multivariate cox proportional hazards model for developing type 1 diabetes * bonferroni - corrected p = 0.007 . not applicable , since there were no diabetes cases in the 37 nonsingleton birth children . islet autoantibodies precede the development of type 1 diabetes and were identified in multiple samples from 147 of the babydiab children . however , there was no increase in the risk of islet autoantibodies in children who were delivered by cesarean section ( 13.8% ; 95% ci 9.917.7% ) compared with children with vaginal delivery ( 13% ; 1016% ; p = 0.6 ; fig . no differences between cesarean section and vaginal delivery were also observed for the probability of developing autoantibodies associated with thyroid autoimmunity and celiac disease ( supplementary fig . 2c , the rate of progression from the development of islet autoantibodies to overt type 1 diabetes in autoantibody - positive children was higher in children delivered by cesarean section ( 57% within 10 years ; 4173% ) versus children born by vaginal delivery ( 28% ; 1739% ; p = 0.015 ) . this remained significant after adjustment for potential confounding variables associated with cesarean section ( adjusted hr 2.4 ; 1.24.4 ; p = 0.008 ) . cesarean delivery is reported to be accompanied by a change in the infant s microbial and viral environment and immune response ( 5 ) . in addition to hla class ii genes ( 17 ) , the viral immune response  associated gene ifih1 is associated with type 1 diabetes development in our cohort ( 9 ) , and the cd25 gene and ptpn22 gene affect both immune response and type 1 diabetes risk ( 7 ) . we therefore examined genotypes of these four gene regions for association with type 1 diabetes and for possible interactions with cesarean section in the association with type 1 diabetes risk . with respect to association , a multivariate cox proportional hazards model showed that hla dr / dq genotype ( adjusted hr 7.3 ; 95% ci 4.013.4 ; p < 0.0001 ) , ifih1 genotype ( 2.4 ; 1.34.5 ; p = 0.005 ) , and cesarean section ( 2.7 ; 1.54.9 ; p = 0.001 ) contributed to the probability of developing type 1 diabetes in the babydiab cohort ( fig . permutation analysis in the multivariate cox model confirmed that hla dr / dq genotype ( p < 0.01 ) , ifih1 genotype ( p < 0.01 ) , and cesarean section ( p < 0.01 ) were associated with type 1 diabetes risk and further suggested an association with cd25 genotype ( p = 0.04 ) , but not ptpn22 genotype ( p = 0.49 ) , in the cohort . type 1 diabetes outcome and risk according to delivery mode and type 1 diabetes susceptibility genes . type 1 diabetes outcome stratified for delivery mode or the type 1 diabetes susceptibility genes is shown in the left - hand column . delivery mode is categorized as cesarean section or vaginal delivery , hla is categorized as teddy - defined risk genotypes or other , and snp genotype is categorized as homogeneous for the common allele versus other . * the reference group used to calculate adjusted hrs in the cox proportional hazards model is indicated for each covariate ( ref ) . the adjusted hrs ( large dots ) and 95% cis ( error bars ) for type 1 diabetes in the multivariate cox proportional hazards model are shown in the diagram . the model also included potential confounder variables associated with cesarean section in the babydiab study ( table 1 ) . the p values are obtained from the multivariate cox proportional hazards model . to search for potential interaction between cesarean section and susceptibility genes in influencing type 1 diabetes risk , we first added the interaction item cesarean sectiongenotype for each of the genes in the cox proportional hazards model . hrs for the interaction item were suggestive of interaction for ifih1 ( adjusted hr 2.3 ; p = 0.18 ) and for cd25 ( 0.2 ; p = 0.04 ) , but not for hla ( 0.96 ; p = 0.9 ) , prompting further analysis . we then examined type 1 diabetes risk associated with cesarean section conditioned by the genotypes of each of these three gene regions ( fig . 4 ) . adjusted hrs for cesarean section were similar for both hla risk and nonrisk genotypes , again suggesting that there was no interaction between cesarean section and hla genotype . in contrast , there were pronounced differences in adjusted hrs of cesarean section between children with risk and nonrisk genotypes at the ifih1 and cd25 genes , again suggesting interaction . interactions between cesarean section and type 1 diabetes susceptibility genes . a : adjusted hrs ( large dots ) for cesarean section versus vaginal delivery as a risk for type 1 diabetes are shown after stratification for genotype at hla , ifih1 , and cd25 genes . for the ifih1 and cd25 snps , the risk genotype used was the homozygous common allele , which is consistent with a recessive susceptibility model . b and c : kaplan - meier survival curves for type 1 diabetes risk according to delivery mode stratified for ifih1 ( b ) and cd25 ( c ) genotype . type 1 diabetes development curves for cesarean section and vaginal delivery are shown as thick and thin lines , respectively , and the color codes represent children with the type 1 diabetes susceptible ( blue ) and nonsusceptible ( green ) genotypes , as predicted by recessive susceptibility models . numbers under the abscissa are the number of children still followed at each time point . finally , we performed kaplan - meier analyses after stratification for ifih1 and cd25 genotypes . for the ifih1 genotypes examined , the increased risk associated with cesarean section was only evident in children who had both the diabetes - susceptible ifih1 gg genotype and cesarean section . the probability of type 1 diabetes by age 12 years in children with the ifih1 gg genotype was 9.1% ( 95% ci 4.913.3 ) in individuals delivered by cesarean section versus 2.8% ( 0.94.7 ) in individuals delivered vaginally ( pcorrected = 0.014 ) . in comparison , the probability for developing type 1 diabetes in children with the ga or aa ifih1 genotypes was 2.8% ( 0.84.8 ) if delivered by cesarean section and 1.7% ( 0.52.9 ; pcorrected = 0.9 ) if delivered vaginally . for cd25 , cesarean section was associated with increased risk for type 1 diabetes , regardless of cd25 genotype . however , there was a markedly reduced 12-year risk for type 1 diabetes in children who had nonsusceptible genotypes and vaginal delivery ( 0.6% ; 0.11.4 ) compared with all other groups : nonsusceptible genotypes and cesarean section , 5.7% ( 2.58.9 ; pcorrected = 0.0005 ) ; susceptible genotypes and vaginal delivery , 3.2% ( 1.64.8 ; pcorrected = 0.04 ) ; and susceptible genotypes and cesarean section , 5.9% ( 3.18.7% ; pcorrected = 0.0007 ) . delivery by cesarean section has become more prevalent over recent decades . in this prospective study of children who are genetically at risk for type 1 diabetes and who have been followed from birth , we found that delivery by cesarean section is associated with a more than twofold increase in the risk of developing type 1 diabetes . notably , this increase was not accompanied by higher numbers of children developing islet autoimmunity , but by a faster progression from the onset of islet autoimmunity to overt diabetes . moreover , the data were indicative of an interaction between cesarean section and the type 1 diabetes susceptible immune response genes ifih1 and cd25 , suggesting that cesarean section could affect the risk for type 1 diabetes by modifying the host s environment and immune response . this is the first prospective longitudinal study of children followed from birth in which cesarean section was examined as a risk factor . the prospective nature of this study , which includes the assessment of islet autoantibodies and onset of overt diabetes , allowed us to distinguish between the risk for autoimmunity and the risk for progression to diabetes . potential limitations of the study are that it is not population - based and that it is limited to children who have a parent , most commonly mothers , with type 1 diabetes . nevertheless , the association between cesarean section and type 1 diabetes was strong in children of nondiabetic mothers , suggesting that the findings may be representative of the broader population . it should also be considered that the associations observed here could be secondary to confounding factors , particularly those that are associated with high rates of cesarean section . however , none of the factors associated with an increased prevalence of cesarean section in the babydiab cohort were associated with an increased risk for type 1 diabetes . additional potential confounding factors are social status and maternal care , which could not be formally analyzed in the babydiab cohort . smoking during pregnancy is associated with lower social economic status , but was not significantly associated with the risk for type 1 diabetes in the babydiab cohort ( data not shown ) . previous studies have suggested that cesarean section is a risk factor for type 1 diabetes ( 1820 ) . our findings that cesarean section is more prevalent in women with type 1 diabetes , in premature births , and in multiparous births are also consistent with previous reports ( 21 ) . inconsistent with previous reports is the magnitude of the increased risk for type 1 diabetes associated with cesarean section in our cohort . our study finds that cesarean section more than doubles risk , whereas the meta - analysis of previous case - control studies estimated a 2030% increase in risk ( 4 ) . our study differs from previous analysis in that it is performed in children with an a priori type 1 diabetes family history . it is possible that the influence of cesarean section on type 1 diabetes risk is enhanced in cohorts rich in type 1 diabetes susceptibility genotypes , such as in the babydiab cohort . the observation is intriguing that cesarean section increases risk for type 1 diabetes and that the prevalence of cesarean section in children born to mothers with type 1 diabetes is high . this result appears at odds with the fact that children born to mothers with type 1 diabetes have a lower risk for diabetes than children born to fathers with type 1 diabetes and nondiabetic mothers ( 22 ) . however , it is important to note that within the babydiab cohort , the reduced risk for type 1 diabetes seen in children of mothers with type 1 diabetes is associated with protection against the development of islet autoimmunity ( 23 ) , whereas cesarean section only affected the rate of progression from islet autoimmunity to overt diabetes . thus , it appears that the type 1 diabetes protection associated with maternal diabetes is strong and potentially hierarchical over increased risk provided by cesarean section . this is consistent with the fact that autoimmunity is almost always observed before the development of type 1 diabetes , implying that it is an important prerequisite for disease . in terms of how cesarean section increases the risk for type 1 diabetes , our findings suggest that the overall risk for autoimmunity , including autoimmunity seen in thyroid and celiac disease , was not affected and suggest that the period after the initiation of autoimmunity is influenced in some way . to consolidate this notion , we examined relationships between cesarean section and genetic susceptibility . we reasoned that factors influencing progression to diabetes should have little or no interaction with genes that mainly affected the risk for developing islet autoantibodies , but that there could be interaction with genes that also affected progression . hla strongly affects the risk for autoantibodies and only minimally , if at all , progression to diabetes ( 17,24,25 ) . notably , and consistent with our reasoning , cesarean section provided a similar increase in the risk for type 1 diabetes in children with and children without high - risk hla genotypes . in contrast to hla , the ifih1 gene influences progression from autoimmunity to type 1 diabetes in our cohort ( 9 ) . unlike what we observed for the hla genotype , stratification for the ifih1 genotype suggested interaction between cesarean section and the ifih1 gene . cesarean section had an hr for type 1 diabetes in children with a susceptible ifih1 genotype that was twice that observed in children with nonsusceptible ifih1 genotypes . moreover , the probability of developing type 1 diabetes was increased only when children were delivered by cesarean section and had the high - risk ifih1 genotype . relevant to our findings , both the ifih1 gene and cesarean section affect innate and adaptive immunity . ifih1 triggers the secretion of immune mediators , such as interferons , in response to viral infection ( 26 ) . these mediators inhibit viral replication and enhance the expression of surface major histocompatibility complex-1 molecules , which are relevant to the destruction of -cells by cd8 t lymphocytes ( 27 ) . cesarean section is associated with stronger nonspecific humoral immune responses and with a marked variation in the microbiome of children , with fewer bifidobacteria at an early age ( 5 ) . the gut microbiome has been suggested to be skewed in a similar manner in children who progress to diabetes ( 28 ) . consistent with this , the hygiene hypothesis suggests that children with reduced or delayed exposure to infection may have an increased risk for type 1 diabetes ( 29 ) . of interest , a second immune response gene associated with type 1 diabetes , cd25 , also showed evidence of interaction with cesarean section in modifying the risk for type 1 diabetes in our cohort , whereas the ptpn22 gene showed little effect on type 1 diabetes risk in our cohort . whereas we are eager to suggest mechanisms involving the immune response effects of cesarean section , it is also possible that cesarean section modifies parental behavior and that this is the primary reason for the observed associations with type 1 diabetes . in conclusion , they further suggest that cesarean section increases the risk for the progression to type 1 diabetes after the initiation of islet autoimmunity , and this increased risk appears to be influenced by environment response genes . these data support the notion that environmental factors can act on disease pathogenesis after autoimmunity has initiated , which is consistent with recent reports of an association of enterovirus infection with type 1 diabetes progression in the diabetes autoimmunity study in the young ( daisy ) study ( 30 ) and with findings in animal models of autoimmune diabetes ( 31 ) . second , they expose novel possibilities to interfere with rate of progression to type 1 diabetes in children who have already mounted an immune response to pancreatic islet -cell antigens , which include treatments that affect the host s immune response to environmental factors .
objectivethe incidence of type 1 diabetes is increasing . 
 delivery by cesarean section is also more prevalent , and it is suggested that cesarean section is associated with type 1 diabetes risk . 
 we examine associations between cesarean delivery , islet autoimmunity and type 1 diabetes , and genes involved in type 1 diabetes susceptibility.research design and methodscesarean section was examined as a risk factor in 1,650 children born to a parent with type 1 diabetes and followed from birth for the development of islet autoantibodies and type 1 diabetes.resultschildren delivered by cesarean section ( n = 495 ) had more than twofold higher risk for type 1 diabetes than children born by vaginal delivery ( hazard ratio [ hr ] 2.5 ; 95% ci 1.44.3 ; p = 0.001 ) . 
 cesarean section did not increase the risk for islet autoantibodies ( p = 0.6 ) but was associated with a faster progression to diabetes after the appearance of autoimmunity ( p = 0.015 ) . cesarean section  associated risk was independent of potential confounder variables ( adjusted hr 2.7;1.55.0 ; p = 0.001 ) and observed in children with and without high - risk hla genotypes . 
 interestingly , cesarean section appeared to interact with immune response genes , including cd25 and in particular the interferon - induced helicase 1 gene , where increased risk for type 1 diabetes was only seen in children who were delivered by cesarean section and had type 1 diabetes 
 susceptible ifih1 genotypes ( 12-year risk , 9.1 vs. < 3% for all other combinations ; p < 0.0001).conclusionsthese findings suggest that type 1 diabetes risk modification by cesarean section may be linked to viral responses in the preclinical autoantibody - positive disease phase .