Risk Factors,metabolic Characteristics Of Gestational Diabetes Mellitus And The Relationship Between GLP-1R Gene Polymorphisms And Gestational Diabetes Mellitus

Gestational diabetes mellitus（GDM）is defined as“any degree of glucose intolerance during pregnancy,excluding overt diabetes in pregnancy”.GDM is one of the most common complications during pregnancy.GDM has become an important public health concern worldwide due to its adverse outcomes for both mothers and their offspring.Cesarean section,dystocia,macrosomia and neonatal hypoglycemia are the most common perinatal complications of GDM.In addition,women with a history of GDM and their offspring are more likely to become obese and develop type 2 diabetes mellitus（T2DM）,metabolic syndrome and cardiovascular disease in the long-term.Currently,the diagnosis of GDM depends on the oral glucose tolerance test（OGTT）at24～28 weeks of gestation when the pregnant women and the fetus have been affected by the hyperglycemic status.Due to the lack of early diagnostic biomarkers of GDM and the uncertain safety of clinical drugs,it is particularly important to reduce the incidence of GDM and the short-term and long-term effects on the mothers and their offspring by screening and managing high risk pregnant women through high risk factors in early pregnancy.The etiology and pathogenesis of GDM remain vague due to its complexity under the combined action of environmental and genetic factors.GDM is a group of clinical syndromes based on multigene inheritance characterized by hyperglycemia and disturbances of glucose,lipids,protein,water,and electrolytes caused by relative and/or absolute insufficiency of insulin due to hormonal changes,chronic low-grade inflammation,weight gain,and changes in eating and exercise habits during pregnancy.Due to the differences in genetic background and living environment,pregnant women with GDM in different regions show different metabolic characteristics and have different effects on pregnancy outcome.It is very important to explore the metabolic characteristics of GDM in the local population for targeted prevention and management.It is also useful for understanding and explaining the mechanism of GDM.Although the pathogenesis of GDM is still not entirely clear,it is generally believed that insulin resistance and pancreaticβcells dysfunction are the main pathogenesis of GDM.To meet the energy needs of the growing fetus by limiting the mother’s consumption of glucose,insulin sensitivity decreases.Pregnant women with normal glucose tolerance（NGT）can compensate for increasing insulin resistance by increasing the secretion of insulin,while women with GDM have insufficient insulin secretion.GDM occurs when pancreaticβcell fail to compensate for increased insulin resistance.Genetic variants of glucagon-like peptide-1 receptor（GLP-1R）have been reported to be associated withβcell function and affect insulin secretion and susceptibility of T2DM,so they may also play an important role in the pathogenesis of GDM and affect susceptibility of GDM.Exploring the relationship between GLP-1R polymorphism and GDM is helpful to discover the genetic susceptibility genes of GDM,and has important significance for the etiology and mechanism of GDM.ObjectiveThe purpose of this study was to provide a scientific basis for the prevention,management,and interpretation of etiology and mechanism of GDM through analyzing the incidence and risk factors of GDM in Jingzhou and evaluating the risk degree of each factor,describing the metabolic characteristics of GDM and assessing their effects on perinatal outcomes,and exploring the relationship between GLP-1R polymorphism and susceptibility to GDM and valuing the influences of GLP-1R polymorphism on glucose metabolism.MethodsWe recruited 1588 subjects from Jingzhou Hospital Affiliated to Yangtze University and Gongan County Maternal and Child Health Care Hospital in Jingzhou,Hubei Province,and established the"Jingzhou maternal and child health cohort".Three nested case-control studies were conducted based on this prospective cohort with gestational age as the time axis.The three studies were conducted in the first trimester,the second trimester and the third trimester,corresponding to the three parts of this study.1.The first part included 237 pregnant women with GDM（case group）and 1315pregnant women with NGT（control group）selected from the cohort according to the inclusion and exclusion criteria.The incidence of GDM was calculated,and the risk factors of GDM were analyzed according to the socioldemographic data,medical history,clinical characteristics and laboratory results of the subjects.First,social demographic variables,clinical characteristics variables and laboratory test results variables were compared between the case group and the control group to screen out the variables with differences,and then all the variables with differences between the two groups were respectively carried out univariate logistic regression analysis.Finally,all variables associated with GDM in univariate logistic regression analysis were included in multivariate logistic regression analysis to explore independent risk factors for GDM of the local population.2.The second part was a 1:1 paired case-control study.All subjects with GDM in the first part were selected into the case group and each GDM subject was matched to one control in the control group of the first part according to the matching criteria.Finally,200 pregnant women with GDM and 200 pregnant women with NGT were included according to the inclusion and exclusion criteria and genotyped for five tag SNPs of GLP-1R using Sanger sequencing.Binary logistic regression was used to evaluate the relationship between GLP-1R polymorphisms and GDM risk.All subjects underwent 75g OGTT at 24～28 weeks to measure fasting plasma glucose（FPG）,1-hour plasma glucose（1h PG）and 2-hour plasma glucose levels,and 109 pairs of pregnant women were tested for OGTT-based fasting insulin（FINS）,1-hour insulin and 2-hour insulin concentrations.Several measured and calculated indices were used to evaluate theβcell function of the individuals with different genotypes and analyze the effect of GLP-1R gene polymorphisms on glucose metabolism.3.The third part included 192 subjects with GDM and 191 subjects with NGT selected from all the subjects in the second part excluding the subjects without delivery data.Several indices were calculated to describe the metabolic characteristics of the subjects based on the concentrations of glucose and insulin in the second part.The relationship between glucose metabolism parameters and pregnancy outcomes was evaluated using stepwise linear regression and binary logistic regression.Results1.The incidence and risk factors of GDM1.1 Among the 1552 subjects,237 subjects developed GDM.The incidence of GDM was 15.27%.The incidence of GDM is 13.27%in pregnant women under the age of 30years old,16.39%in those between 31 and 34 years old,and 22.75%in those who are at least 35 years old.The incidence of GDM was 13.31%in subjects with normal weight（BMI:18.5～23.9 kg/m²）,13.33%in lean women（BMI<18.5 kg/m²）,and 19.35%in overweight women（BMI:24～27.9 kg/m²）,and 25.00%in obese people（BMI≥28 kg/m²）.1.2 The risk of GDM in pregnant women older than 35 years was 1.997 times higher than that in pregnant women younger than 30 years.The risk of GDM was 1.617 times and 1.864 times higher in overweight and obese pregnant women than in normal weight pregnant women.The risk of GDM in pregnant women with endocrine diseases was 4.404times higher than that in pregnant women without endocrine diseases.The risk of GDM increased by 10.4%for every extra kilogram of weight gained.For every 1mm Hg increase of diastolic blood pressure during early pregnancy,the risk of GDM increased by 5%.The risk of GDM increased by 246.5%for every 1 mmol/L increase of fasting blood glucose and 2.1%for every 1 U/L increase of alanine aminotransferase in early pregnancy.Freelance work or other occupations of a pregnant woman’s spouse was a protective factor for GDM.2.The effects of GLP-1R polymorphisms on GDM susceptibility and glucose metabolism2.1 Mutant genotype AG+GG of GLP-1R tag SNP rs6458093 increased GDM risk（P=0.049）,especially among subjects younger than 35 years（P=0.024）and with BMI no less than 24 kg/m²（P=0.041）after adjusting for confounders.2.2 Compared with subjects with wild genotype AA,subjects with genotype AG+GG of GLP-1R tag SNP rs6458093 also showed significantly lower insulinogenic index at 60min(IGI₆₀)（P=0.032）and disposition index（DI）（P=0.029）,as well as significantly higher 1-hour plasma glucose levels（P=0.045）.2.3 The mutant heterozygous genotype GA of GLP-1R tag SNP rs3765467 decreased GDM risk among subjects older than 35 years（P=0.037）but showed no association with insulin secretion and glucose homeostasis.3.Metabolic characteristics of GDM and the effects on pregnancy outcomes3.1 Compared with the NGT group,the GDM group showed significantly higher fasting and postprandial glucose parameters but significantly lower fasting and postprandial insulin responses.Meanwhile,the GDM group had significantly lower homoeostasis model assessment ofβcell function（HOMA-β）,DI and Matsuda insulin sensitivity index(ISI_Matsuda)but comparable homoeostasis model assessment of insulin resistance.3.2 The impaired fasting glucose（IFG）subgroup showed significantly lower FINS/FPG only,while the impaired glucose tolerance（IGT）and impaired fasting and stimulated glucose（IFSG）subgroups showed deficiency in both fasting and postprandial insulin response.The IFSG subgroup had the highest glucose parameters and the lowest insulin parameters,as well as significantly lower ISI_Matsuda and HOMA-βthan the NGT group.3.3 The higher the level of FPG,the heavier the birth weight.The higher the 1h PG and FINS/FPG values,the earlier the gestational age of delivery.The area under the insulin curve（AUC-INS）,IGI₆₀ and DI were related to premature delivery risk after adjusting for confounders.The IFG subgroup of GDM was 2.319 times more likely to be subjected to cesarean section than the NGT group.FPG,FINS/FPG,area under the glucose curve（AUC-GLU）,AUC-INS/AUC-GLU and HOMA-βwere related to macrosomia risk.Conclusion1.The incidence of GDM in Jingzhou was 15.27%.Advanced age（over 35 years old）,overweight or obese before pregnancy,rapid weight gain during pregnancy,high blood pressure,FPG or ALT in early pregnancy and endocrine diseases were independent risk factors for GDM.Freelance work or other occupations of a pregnant woman’s spouse was a protective factor for GDM.2.Tag SNP rs6458093 of GLP-1R was associated with increased GDM risk and affectedβcell function and postprandial glucose metabolism,and mutant genotype AG+GG of rs6458093 might be a risk factor for GDM.Tag SNP rs3765467 of GLP-1R was associated with decreased GDM risk,and mutant heterozygote genotype GA might be a protective factor for GDM.3.βcell dysfunction rather than insulin resistance determined the occurrence of GDM in Jingzhou pregnant women.Women with GDM had a similar risk of adverse perinatal outcomes to women with NGT in this study.The IFG group might have a different pathogenesis from the IGT and IFSG groups and that IGT might be a transitional stage of IFSG.Several glucose metabolism parameters（especially FPG）were associated with adverse perinatal outcomes and could be used as indicators to monitor glucose metabolism during pregnancy.