Gestational diabetes mellitus (GDM), sometimes called diabetes of pregnancy, is a disorder of glucose metabolism that is first diagnosed during pregnancy and does not meet the criteria for overt diabetes. It is one of the most common medical complications of pregnancy. In Germany, GDM is documented in approximately 9.6% of pregnancies, and its prevalence has continued to increase.
GDM must be distinguished from diabetes that was already present before pregnancy or from diabetes first detected during pregnancy that already meets the diagnostic criteria for overt diabetes. In such cases, the condition is classified as diabetes diagnosed in pregnancy, rather than gestational diabetes.
When GDM is detected early and treated appropriately, glucose levels can usually be managed successfully and the risk of complications can be substantially reduced. The goal, however, is not to achieve a perfect glucose value at every single measurement. What matters most is the overall pattern: how often glucose values are elevated, how high they rise, how long elevations persist, and how the baby is growing.
Why Does Gestational Diabetes Develop?
Insulin sensitivity changes during pregnancy. In early pregnancy it may even increase slightly, whereas insulin resistance progressively rises during the second and particularly the third trimester because of placental hormones and other metabolic adaptations.
This physiological insulin resistance helps ensure an adequate supply of nutrients to the growing fetus. Most pregnant women compensate by increasing pancreatic insulin secretion. If pancreatic beta cells cannot produce enough additional insulin, maternal glucose levels rise.
The underlying mechanism therefore resembles type 2 diabetes: increasing insulin resistance combined with insufficient beta-cell compensation.
Who Is at Increased Risk?
The risk of GDM increases with maternal age and higher body weight. Particularly important risk factors include GDM in a previous pregnancy, diabetes in first-degree relatives, previous delivery of a large-for-gestational-age infant, and ethnic backgrounds associated with a higher prevalence of type 2 diabetes. Ovulation induction or assisted reproductive treatment may also be associated with increased risk.
A rigid age threshold such as 45 years is therefore not useful. Women with relevant risk factors should be assessed early in pregnancy for previously unrecognized disturbances of glucose metabolism or overt diabetes. The DDG recommends early testing before 24 weeks of gestation in women at increased risk.
In Germany, screening for gestational diabetes is part of routine prenatal care.
Under the German maternity guidelines, screening usually begins with a 50-g glucose challenge test between 24+0 and 27+6 weeks of gestation. The woman does not need to be fasting. Fifty grams of glucose are consumed, and venous plasma glucose is measured one hour later.
If the 1-hour value is ≥135 mg/dl (7.5 mmol/l), a diagnostic 75-g oral glucose tolerance test (OGTT) is required. At very high screening values around or above 200 mg/dl (11.1 mmol/l), the 75-g OGTT may be omitted; further assessment with fasting glucose and/or HbA1c is required to distinguish GDM from overt diabetes. (Gemeinsamer Bundesausschuss)
From a diabetological perspective, the DDG favors performing the 75-g OGTT directly between 24+0 and 27+6 weeks of gestation. One reason is that the two-step screening procedure may miss women whose only abnormal value is fasting glucose.
The test should be performed in the morning after an overnight fast of at least eight hours. During the three days before the test, the woman should follow her usual diet and should not deliberately restrict carbohydrate intake.
First, fasting venous plasma glucose is measured. The woman then drinks 75 g of glucose dissolved in approximately 300 ml of water, usually within three to five minutes. Further venous blood samples are obtained after one and two hours.
During the test, the woman should remain seated and avoid unnecessary physical activity. Smoking is not permitted. Acute illness, significant vomiting, unusual physical exertion, or certain medications may interfere with the test and can require postponement.
Diagnosis requires a quality-controlled measurement of venous plasma glucose. Capillary self-monitoring meters are not appropriate for diagnosing GDM, although they are suitable for subsequent glucose monitoring at home.
When Is Gestational Diabetes Diagnosed?
The IADPSG thresholds used in the German guideline are:
Time of measurement |
Diagnostic threshold |
Fasting |
≥92 mg/dl (5.1 mmol/l) |
1 hour after glucose |
≥180 mg/dl (10.0 mmol/l) |
2 hours after glucose |
≥153 mg/dl (8.5 mmol/l) |
One value reaching or exceeding the threshold is sufficient for the diagnosis of GDM.
A fasting plasma glucose level of ≥126 mg/dl (7.0 mmol/l) suggests overt diabetes rather than GDM and requires appropriate confirmation and classification. A 2-hour glucose level of ≥200 mg/dl (11.1 mmol/l) during the OGTT also meets a criterion for diabetes.
When maternal glucose levels are elevated, more glucose crosses the placenta. Maternal insulin itself does not cross the placenta to a clinically relevant degree, but the fetal pancreas responds to the increased glucose supply by producing more insulin.
Fetal hyperinsulinemia promotes fat deposition and increased abdominal growth. Consequently, the risk of a large-for-gestational-age infant, macrosomia and shoulder dystocia increases. Neonatal hypoglycemia, respiratory problems, hyperbilirubinemia and the need for neonatal monitoring are also more common.
For the mother, GDM is associated with increased risks of pregnancy-induced hypertension, preeclampsia and cesarean delivery.
The large HAPO study demonstrated an important principle: there is no sharp glucose threshold at which risk suddenly begins. Instead, the risk of several adverse pregnancy outcomes increases progressively as maternal glucose levels rise. (New England Journal of Medicine)
This means that a single value of, for example, 145 mg/dl rather than 140 mg/dl does not mean that harm has occurred to the baby.
Good Glucose Values — Not Perfect Glucose Values
For home glucose monitoring, the current German DDG targets are:
Measurement |
Target |
Fasting or before meals |
65–95 mg/dl (3.6–5.3 mmol/l) |
1 hour after the start of a meal |
<140 mg/dl (7.8 mmol/l) |
2 hours after the start of a meal |
<120 mg/dl (6.7 mmol/l) |
The ADA 2026 recommendations are very similar, although for insulin-treated pregnancies the lower fasting/preprandial limit is generally stated as 70 mg/dl.
These values are treatment targets, not boundaries separating “safe” from “dangerous.”
The DDG explicitly emphasizes that adverse consequences for the child cannot be inferred from occasional isolated target-value exceedances. What matters is whether elevated values occur repeatedly.
Which Glucose Patterns Are Actually Concerning?
Repeatedly elevated fasting glucose, frequent post-meal elevations and prolonged hyperglycemia deserve particular attention.
According to the DDG, insulin therapy should generally be considered if lifestyle measures do not achieve the glucose targets and more than 50% of values in a one-week glucose profile exceed the relevant target. This also applies if the problem is confined to fasting glucose or to values after one particular meal.
Repeated fasting glucose values of ≥110 mg/dl (6.1 mmol/l) are particularly important because fasting hyperglycemia is often difficult to correct with diet and exercise alone; in this situation, insulin treatment may be started promptly.
Even less marked isolated fasting hyperglycemia can justify treatment when more than half of fasting values remain above the fasting target despite appropriate lifestyle measures.
At the other extreme, unnecessarily low glucose levels are not desirable. In women receiving insulin, recurrent or severe hypoglycemia should be avoided.
“The lower the better” is not the correct principle during pregnancy.
For most women, treatment begins with individualized nutritional counselling, regular physical activity and frequent glucose monitoring during the first one to two weeks.
Nutrition must provide adequate energy, protein, vitamins, minerals and other nutrients for both mother and fetus. Severe carbohydrate restriction or ketogenic diets are inappropriate during pregnancy. The DDG recommends that carbohydrates generally provide approximately 40–50% of energy intake and that intake should not fall below about 40% of daily energy or approximately 116 g/day. High-fibre, slowly absorbed carbohydrates are preferable.
Distributing carbohydrates across several meals can help reduce postprandial glucose excursions. Carbohydrate intake is often kept somewhat lower at breakfast because morning postprandial glucose levels may rise more markedly.
Regular moderate exercise improves insulin sensitivity. A brisk walk after a meal can substantially reduce the subsequent glucose rise. The DDG recommends, where medically appropriate, approximately 30 minutes of brisk walking on at least three days per week, and preferably regular activity throughout the week.
If nutrition and physical activity are not sufficient to achieve glucose targets, insulin is the preferred pharmacological treatment.
Needing insulin does not mean that the woman has done anything wrong. Insulin resistance normally increases as pregnancy progresses, mainly because of placental hormones. Some women simply cannot compensate sufficiently by increasing their own insulin production.
Approximately 20–30% of women with GDM require insulin therapy.
Insulin does not cross the placenta in clinically relevant amounts. It lowers maternal glucose and thereby reduces excessive glucose delivery to the fetus.
he older concept that modern long-acting insulin analogues are generally unsuitable during pregnancy is no longer correct.
Both human insulin and appropriate short- and long-acting insulin analogues can be used during pregnancy. Rapid-acting analogues such as insulin aspart and insulin lispro are well established. Modern rapid-acting formulations and suitable basal insulin analogues may also be used according to the individual clinical situation.
For women with pre-existing type 1 or type 2 diabetes, the German recommendations state that both short- and long-acting insulin analogues can be appropriate and may offer advantages when strict glucose targets are required.
That statement would also be too simplistic. Nevertheless, insulin remains the preferred treatment for GDM.
Most oral or injectable glucose-lowering medications used for type 2 diabetes — including sulfonylureas, DPP-4 inhibitors, SGLT2 inhibitors and GLP-1 receptor agonists — are not recommended for routine use during pregnancy.
Metformin crosses the placenta. It should therefore not be considered equivalent to insulin as standard first-line treatment for GDM. The DDG allows consideration of metformin in selected women with particularly marked insulin resistance after individualized specialist assessment and appropriate counselling. In Germany, its use for GDM is not routine first-line therapy.
For pre-existing type 2 diabetes, insulin also remains the preferred treatment. Metformin may be considered as an adjunct in selected women with marked insulin resistance, rather than as routine replacement for insulin.
Maternal glucose levels are only one component of GDM management. Fetal growth must also be considered.
Ultrasound measurement of the fetal abdominal circumference (AC) is particularly informative because disproportionate abdominal growth is associated with fetal hyperinsulinemia and excessive nutrient supply.
If the fetal abdominal circumference is at or above approximately the 75th percentile, particularly in combination with additional risk factors, clinicians may choose to start insulin more readily and aim for somewhat stricter glucose control.
If fetal growth remains appropriate and the abdominal circumference is below the 75th percentile, occasional minor glucose elevations may be tolerated more readily.
Fixed alternative targets such as “85/120 mg/dl” based solely on fetal size should therefore not be used as a rigid universal table. Treatment targets should be individualized.
During the third trimester, fetal biometry is generally repeated at intervals of approximately two to three weeks, with shorter intervals when growth abnormalities are suspected.
Extreme diets, prolonged fasting, severe carbohydrate restriction or deliberately eating too little simply to obtain lower glucose readings should be avoided.
Repeated marked hyperglycemia should not be ignored. Likewise, women taking insulin should not accept recurrent or severe hypoglycemia as the inevitable price of good glucose control.
At the same time, treatment should not create anxiety every time a glucose value is slightly above target.
For women whose GDM remains well controlled, the frequency of finger-stick measurements can often be reduced after the initial assessment period. According to the DDG, if all values remain within target during the first one to two weeks, monitoring may be reduced to rotating measurements on individual days or several complete daily profiles each week.
Continuous glucose monitoring (CGM) provides hundreds of glucose readings every day and can reveal postprandial peaks, nocturnal patterns and glucose variability that may not be apparent from a few finger-stick measurements.
In pregnancy complicated by type 1 diabetes, CGM has clear benefits and is recommended. It improves time in the pregnancy-specific target range and is associated with improved neonatal outcomes. (Diabetes Journals)
The situation is different for GDM. Current evidence is insufficient to recommend CGM routinely for every woman with GDM. Some studies demonstrate improvements in glucose metrics, but a consistent improvement in clinically important pregnancy outcomes has not yet been established. CGM can nevertheless be useful in selected women, particularly those receiving insulin or those with highly variable glucose profiles. (Diabetes Journals)
CGM can also create unnecessary anxiety. Instead of four glucose measurements per day, a woman suddenly sees several hundred readings.
The most important principle therefore remains:
Look at the overall glucose pattern — not every individual peak in the curve.
Automated Insulin Delivery Systems
Automated insulin delivery (AID) systems combine CGM, an insulin pump and an algorithm that automatically adjusts insulin delivery.
The evidence for these systems in pregnancy complicated by type 1 diabetes has developed rapidly. In the AiDAPT randomized trial, hybrid closed-loop treatment increased the pregnancy-specific time in range by approximately 10.5 percentage points, equivalent to roughly 2.5 additional hours per day, without a significant increase in hypoglycemia. (New England Journal of Medicine)
The ADA Standards of Care 2026 now recommend AID systems with pregnancy-specific glucose targets for pregnant women with type 1 diabetes. Systems without pregnancy-specific targets may also be considered in selected patients when managed by experienced teams. (Diabetes Journals)
For ordinary gestational diabetes, however, an AID system is generally unnecessary. Most women with GDM require either no insulin or a relatively simple insulin regimen.
A useful way of thinking about glucose monitoring is:
A glucose reading is information — not a judgement.
A value above the target range does not mean that damage has occurred to the baby. Even with excellent treatment, occasional fluctuations cannot be completely avoided.
More useful questions are whether fasting values have been elevated over several days; whether glucose is repeatedly high after the same meal; whether a substantial proportion of readings exceeds the target; whether fetal abdominal growth is disproportionate; and whether recurrent hypoglycemia is occurring.
The focus therefore shifts from:
“Was this one value bad?”
to:
“Is there a recurring pattern that requires treatment?”
A single mild glucose elevation is usually not a reason for an emergency call.
Medical review is more important when glucose values are repeatedly and clearly elevated, fasting glucose remains persistently high, glucose levels rise unexpectedly and markedly, recurrent hypoglycemia occurs during insulin therapy, or ultrasound shows unexpected fetal growth.
Very high glucose concentrations accompanied by symptoms such as marked thirst, vomiting, abdominal discomfort, rapid breathing or pronounced weakness require prompt medical evaluation because overt diabetes or, rarely, metabolic decompensation must be excluded.
Intentional substantial weight loss is generally not the goal during pregnancy. Recommended weight gain depends on pre-pregnancy BMI:
Pre-pregnancy BMI |
Recommended total weight gain |
Underweight, BMI <18.5 kg/m² |
12.5–18 kg |
Normal weight, BMI 18.5–24.9 kg/m² |
11.5–16 kg |
Overweight, BMI 25.0–29.9 kg/m² |
7–11.5 kg |
Obesity, BMI ≥30 kg/m² |
5–9 kg |
However, the statement that “weight loss must be avoided under all circumstances” is too absolute. After dietary improvement, a decrease of one or two kilograms during the first weeks is not necessarily concerning, particularly in women with overweight or obesity. Adequate nutrient intake and normal fetal development are more important than the number on the scale alone.
After delivery of the placenta, insulin resistance decreases rapidly. Insulin therapy that was started specifically for GDM can therefore usually be discontinued immediately after delivery.
Follow-up remains essential.
A 75-g OGTT should be performed 6–12 weeks after delivery, regardless of whether the mother is breastfeeding. Fasting glucose alone or HbA1c alone is not sufficiently sensitive for this early postpartum assessment.
The recommended 6–12-week interval is not an absolute deadline. If the test has not been performed during this period, it should still be arranged later. It is particularly important to assess glucose metabolism before another pregnancy.
Women who have had GDM have a markedly increased long-term risk of diabetes. According to the German guideline, approximately 35–60% develop diabetes within ten years, corresponding to roughly a seven- to eightfold higher risk than women with normal glucose tolerance during pregnancy.
Even after a normal postpartum OGTT, long-term screening remains advisable. In Germany, testing approximately every two years is recommended when results remain normal; women with impaired fasting glucose or impaired glucose tolerance require more frequent, usually annual, follow-up.
Modern treatment of GDM has two equally important aims: maintaining glucose concentrations as close to normal as is safely achievable, and providing treatment that is practical, safe and sustainable in everyday life.
Persistent maternal hyperglycemia increases risks for both mother and child, and randomized trials have demonstrated that treatment of GDM improves pregnancy outcomes. (New England Journal of Medicine)
But the other message is equally important:
Occasional glucose excursions are part of real life and do not mean that the baby has been harmed.
The aim is not to perfect every point on a glucose curve. The aim is to recognize clinically relevant patterns, correct them together with the diabetes and obstetric team, monitor fetal development, and avoid both undertreatment and overtreatment.
A woman who already had type 2 diabetes before becoming pregnant does not have gestational diabetes. Pregnancy with pre-existing type 2 diabetes is considered a high-risk pregnancy and should ideally be planned before conception with specialist diabetes and obstetric care.
The German DDG glucose targets during pregnancy are similar to those used for GDM: fasting and preprandial glucose 65–95 mg/dl (3.6–5.3 mmol/l), 1-hour postprandial glucose ≤140 mg/dl (7.8 mmol/l) and 2-hour postprandial glucose ≤120 mg/dl (6.7 mmol/l). The ADA 2026 uses a slightly narrower lower fasting/preprandial boundary of 70 mg/dl for insulin-treated diabetes in pregnancy.
Insulin is the preferred pharmacological therapy. Most oral diabetes medications and GLP-1 receptor agonists should not be used during pregnancy. Metformin may be considered in selected women with marked insulin resistance, usually in addition to insulin, but it is not recommended routinely.
CGM is increasingly useful in pre-existing diabetes. For type 1 diabetes in particular, CGM and pregnancy-adapted automated insulin delivery have become important components of modern treatment. Evidence for routine AID use in pregnancy with type 2 diabetes remains much more limited.