The prevalence of GDM has gradually increased , accompanied by the improved living standard and constantly revised diagnostic criteria for GDM in recent years, threatening the mental and physical health of pregnant women and the safety of the fetus. Despite this, the cause of GDM remains unclear. The generally accepted explanation at the moment is insulin resistance and islet cell damage for various causes , and the exact mechanism is still in controversy . The internationally recognized GDM diagnostic criterion is OGTT at 24-28 weeks of gestation, but as the gestational week is close to the second trimester and earlier intervention is not available, many scholars have been investigating in recent years whether there are reliable screening or diagnostic indicators in early pregnancy.
Some studies have revealed a certain correlation between early-pregnancy FPG, HbA1c, BMI, and GDM . FPG in early pregnancy is the initial screening of blood glucose during pregnancy. Han Wenli et al.  found that fasting blood glucose in early pregnancy has predictive value for GDM, which is consistent with this study. HbA1c is originally used to measure the level of glycemic control in recent months . There has now been a heated debate at home and abroad on whether HbA1c can be used to screen GDM in early pregnancy. Some scholars believe that HbA1c is a stable reflection of blood glucose in the last 3 months. That it allows blood sampling at any time without fasting makes it easier to perform and more acceptable for patients, with better compliance of pregnant women and benefits to clinical work. Besides, HbA1c can not only detect abnormal blood glucose but also monitor the recent situation of blood glucose. In this study, early-pregnancy HbA1c and FPG of pregnant women with GDM were found to be higher than those in the normal control group, which is consistent with Zhao Ming’s study . Regression analysis showed that HbA1c and FPG were high-risk factors for GDM, and high levels of early-pregnancy HbA1c and FPG could predict the occurrence of GDM.
Studies have shown that obese patients have more severe insulin resistance and impaired pancreatic β-cell function, and BMI is an important indicator of obesity in humans. A meta-analysis  showed that overweight and obese pregnant women were 2.01 times more likely to develop GDM than those with a normal BMI. Therefore, diet, lifestyle intervention, and weight control are important part of GDM therapy . Studies by Harper LM et al. and Li et al. suggested that early screening for GDM in obese women can prevent fetal overgrowth and reduce perinatal outcomes such as macrosomia. This study found that pregnant women who developed GDM also had a higher body mass index in early pregnancy than those in the control group. Logistic regression analysis suggested that pregnant women with a high BMI were 1.077 times more likely to develop GDM than those with a low BMI, which proved that BMI in early pregnancy might be a risk factor for GDM. The probability of developing GDM is also lower if some measures are taken in early pregnancy to improve dietary lifestyle and control weight, than that without interventions.
However, there are still some limitations in our study. This study has a relevant small sample size from a single center. Therefore, in the future study, we should do much deeper study on this topic using a large sample size from the multiple center.
In this study, we found that early-pregnancy FPG, HbA1c, and BMI of pregnant women with GDM were higher than those of the normal control group. ROC curve analysis showed that the AUCs of the three tests individually in predicting GDM were 0. 647, 0.661, and 0. 608, with respective sensitivity as 0.588, 0.505, and 0.634, specificity 0.633, 0.745, 0.554; the AUC of combined test 0.736, sensitivity 0.689, specificity 0.640, comprehensively higher than the three indexes that individually predict GDM. Therefore, it was inferred that the combination of BMI, FPG, and HbA1c in early pregnancy has higher diagnostic efficacy and can be used as a means of screening for GDM in early pregnancy. The combined application of the three indicators has higher clinical value and a significantly improved accuracy of GDM screening. At present, a unified standard for early prediction of GDM has not yet come into being in clinical practice, and multicenter prospective randomized controlled trials with large sampling are necessary to provide a solid theoretical basis for early prediction of GDM, early intervention, and less incidence of adverse perinatal outcomes.