[2] Babies born to individuals with poorly treated gestational diabetes are at increased risk of macrosomia, of having hypoglycemia after birth, and of jaundice.

[3] A number of ethnic groups including Asians, American Indians, Indigenous Australians, and Pacific Islanders are at higher risk.

[27] Insulin resistance is a normal phenomenon emerging in the second trimester of pregnancy, which in cases of GDM progresses thereafter to levels seen in a non-pregnant woman with type 2 diabetes.

Multivariate stepwise regression analysis reveals that, in combination with other placental hormones, leptin, tumor necrosis factor alpha, and resistin are involved in the decrease in insulin sensitivity occurring during pregnancy, with tumor necrosis factor alpha named as the strongest independent predictor of insulin sensitivity in pregnancy.

[29] It is unclear why some women are unable to balance insulin needs and develop GDM; however, a number of explanations have been given, similar to those in type 2 diabetes: autoimmunity, single gene mutations, obesity, along with other mechanisms.

β-cell adaption refers to the change that pancreatic islet cells undergo during pregnancy in response to maternal hormones in order to compensate for the increased physiological needs of mother and baby.

[32] The exact mechanism of HGF/c-MET regulated β-cell adaptation is not yet known but there are several hypotheses about how the signaling molecules contribute to insulin levels during pregnancy.

[35] A number of screening and diagnostic tests have been used to look for high levels of glucose in plasma or serum in defined circumstances.

[39] Hemoglobin A1c (HbA1c) is not recommended for diagnosing gestational diabetes, as it is a less reliable marker of glycemia during pregnancy than oral glucose tolerance testing (OGTT).

[35][46] The American Diabetes Association and the Society of Obstetricians and Gynaecologists of Canada recommend routine screening unless the woman is low risk (this means the woman must be younger than 25 years and have a body mass index less than 27, with no personal, ethnic or family risk factors)[5][44] The Canadian Diabetes Association and the American College of Obstetricians and Gynecologists recommend universal screening.

[39] Some pregnant women and care providers choose to forgo routine screening due to the absence of risk factors, however this is not advised due to the large proportion of women who develop gestational diabetes despite having no risk factors present and the dangers to the mother and baby if gestational diabetes remains untreated.

[24] When a plasma glucose level is found to be higher than 126 mg/dL (7.0 mmol/L) after fasting, or over 200 mg/dL (11.1 mmol/L) on any occasion, and if this is confirmed on a subsequent day, the diagnosis of GDM is made, and no further testing is required.

[65] However, data from the Nurses' Health Study shows that adherence to a healthy plant-based diet is associated with lower risk for GDM.

[68] A 2023 review found that a plant-based diet (including fruits, vegetables, whole grains, nuts and seeds, and tea) rich in phytochemicals lowers the risk of GDM.

[69] A Cochrane review, updated 2023, stated that myo‐inositol has a potential beneficial effect of improving insulin sensitivity, which suggested that it may be useful for women in preventing gestational diabetes″.

[71] For women with a normal BMI pre-pregnancy, light to moderate exercise for 30-60 minutes three times a week during pregnancy can decrease the occurrence of GDM.

If GDM is not treated or is made worse, the child may suffer from macrosomia, impaired intrauterine growth, obstetric trauma, hyperbilirubinemia, hypoglycemia, or even infection.

Benefits to resistance and aerobic exercise include maternal decrease in cramps, lower back pain, edema, depression, urinary incontinence, duration of labor, constipation, and the number of c-sections.

These benefits can affect the fetus by having a decreased body fat mass, improved stress tolerance, and advanced neurobehavioral maturation.

The study reviewed by Dipla, et al.,[79] found that even a single exercise bout increases skeletal muscle glucose uptake, minimizing hyperglycemia.

Regular exercise training has been found to promote mitochondrial biogenesis, improve oxidative capacity, enhance insulin sensitivity and vascular function, and reduce systemic inflammation in women with GDM.

[88] Target ranges advised by the Australasian Diabetes in Pregnancy Society are as follows:[16] Regular blood samples can be used to determine HbA1c levels, which give an idea of glucose control over a longer time period.

[89] If monitoring reveals failing control of glucose levels with these measures, or if there is evidence of complications like excessive fetal growth, treatment with insulin might be necessary.

[35][90] A 2016 Cochrane review (updated in 2023) concluded that quality evidence is not yet available to determine the best blood sugar range for improving health for pregnant women with GDM and their babies.

[3] Babies born to women treated with metformin have been found to develop less visceral fat, making them less prone to insulin resistance in later life.

[104] It is currently unclear how much genetic susceptibility and environmental factors contribute to this risk, and whether treatment of GDM can influence this outcome.

[106][107] Research is being conducted to develop a web-based clinical decision support system for GDM prediction using machine learning techniques.

[112] The two main risks GDM imposes on the baby are growth abnormalities and chemical imbalances after birth, which may require admission to a neonatal intensive care unit.

[35] However, the evidence for each of these complications is not equally strong; in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study for example, there was an increased risk for babies to be large but not small for gestational age in women with uncontrolled GDM.

[123] By 2021, the Global prevalence of hyperglycemia in pregnancy (HIP) as per IDF atlas will be 21.1 million people, accounting for 16.7% of births to women aged 20-49.