Gestational Diabetes

last authored: Jan 2012, David LaPierre
last reviewed:





Gestational diabetes mellitus (GDM) is one of the most important complication during pregnancy, occurring in 2-5% of all pregnancies. Diabetes is very important to detect, as sugar levels are directly related to fetal growth and therefore to risk of macrosomia (birthweight >4500g). Risk is also elevated for both mother and fetus, including pyelonephritis, gestational hypertension, miscarriage or stillbirth, prematurity, birth trauma, and neonatal hypglycemia. However, good glycemic control in GDM eliminates the increased risk of death (Sheffield et al, 2002).


In most cases, sugar levels return to normal following delivery, though over 50% of mothers with GDM will develop diabetes in the coming 20 years.


GDM almost always presents in the third trimester. Hyperglycemia present at <20 weeks gestation suggests preexisting diabetes mellitus.




The Case of Alice K.

Alice is a 22 year-old overweight patient of yours who is 24 weeks pregnant. You tell her that you will be screening her for gestational diabetes soon, to which she replies that she hates needles and would much rather not have the test done.

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Causes and Risk Factors

Risk factors include:

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Gestational diabetes arises in a similar manner to type II diabetes, in which there is peripheral insulin resistance mediated by cortisol or placental hormones such as hPL. This insulin resistance leads to hyperglycemia in the mother.

Maternal hyperglycemia, in turn, results in fetal hyperinsulinemia with attending somatic growth.

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Signs and Symptoms

  • history
  • physical exam


Patients are typically asymptomatic. However, marked diabetes can lead to:

  • polyuria
  • polydipsia
  • fatigue

Physical Exam

Edema may be present if hyperglycemia is advanced, though is also common as a normal finding in pregnancy.

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While global consensus is still lacking, selective screening (vs universal) is often done at 24-28 weeks GA for pregnant females age >25, or <25 with any above-mentioned risk factors:

  • lab investigations
  • diagnostic imaging

Lab Investigations

A 50 g glucose tolerance test is commonly used for screening at 24-28 weeks gestation. Results for plasma glucose (PG) one hour after ingestion can show:

  • <7.8 mmol/L (140 mg/dl) - normal
  • > 7.8 and < 11.0 mmol/L (140-180 mg/dL) - further testing required (see below)
  • > 11.0 mmol/L (>180 mg/dL) - diagnostic for gestational diabetes

A two hour, 75g glucose tolerance test may be done if if further testing is required following the one hour test, with testing at 0, 1, and 2 hours. Diagnosis is made if:

  • FPG >5.3 mmol/L
  • 1h PG >10.6 mmol/L
  • 2h PG >9.0 mmol/L

This 2h, 75g test can also be carried out at any stage of the pregnancy, especially when there is a higher risk of developing GDM.


Urinalysis can show glucosuria and can also reveal asymptomatic bacteriuria, which occurs at at least 3 times the rate of nondiabetic women.

Diagnostic Imaging

Ultrasound is often used for ongoing surveillance after 32 weeks GA. This can reveal macrosomia and polyhydramnios (increased levels of aminiotic fluid).


Screening for macrosomia, or infant >90% size for GA, can be helpful to predict obstructed labour, such as can occur with shoulder dystocia, and to lead to discussion around elective cesarian section.

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Differential Diagnosis

The differential of elevated fasting blood glucose includes:

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Control of glucose levels is very important to improve outcomes (Sheffield et al, 2002). A multidisciplinary team should be engaged to provide sufficient care.

Glucose monitoring should be 4x daily, including fasting and postprandial measurements, to provide feedback and motivation. Postprandial measurements are of greater value (DeVeciana et al, 1995).




A diebetic diet should be started. Diet should include calorie restriction (25-35 kcal/kg/d, based on prepregnancy weight) and increased fibre intake. Dietitians play a key role in effective diet control, as do food records.


Regular exercise is crucial, if contraindications such as incompetent cervix are not present. Small, frequent amounts of non-weightbearing or low-impact exercise can be very helpful in decreasing insulin resistance. Engagement of family is important to improve health behaviours.




Insulin should be added if sugars are not controlled with lifestyle measures. Safe insulins include:

The insulin pump can be very helpful to improve control. However, while sugar control does reduce fetal death, the literature is less clear regarding the role of insulin in reducing rates of macrosomia (Langer et al, 1994).


Glyburide also appears to be a safe and effective option during pregnancy, though metformin is normally not used, given the ease with which is crosses the placenta (Saade, 2005).



Prenatal Followup

Regular visits are critical to monitor blood glucose and risk of complications.


Periodic ultrasounds and NST should be done to monitor fetal growth. Induced labour at 39-40 weeks may be necessary if growth is accelerated.


Preterm birth is more common in women with GDM. Tocolytics are often used to buy time for fetal lung maturation using glucocorticoids.



Labour and Delivery

Intrapartum insulin, dextrose, and IV fluids should be given to maintain tight glucose control. Ongoing fetal monitoring should be done to ensure wellbeing, with the cesarian section available if the need arises. Forceps should be avoided when macrosomia is present. The increased risk of shoulder dystocia requires adequate preparation of staff and supplies.


Following delivery, insulin should be reduced as insulin resistance drops. Lowered glucose levels speed healing after vaginal delivery or Caesarean section. Breastfeeding and snacking should be encouraged.


The infant should be monitored for hypoglycemia. A thorough newborn exam should be carried out to ensure there are no malformations or issues with the central nervous system.



Maternal Followup

Blood glucose typically quickly returns to normal after delivery, but should be followed up with a one hour oral glucose tolerance test at 6-12 weeks.

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Consequences and Course

Maternal complications include:

Over 50% of patients develop glucose intolerance later in life, with T2DM following in many cases. Nephropathy and hypertension may also result.


Fetal complications include:

Children born to mothers with GDM are at higher risk of developing T2DM in life, due to genetics but also pancreatic hyperplasia and increased basal insulin production.

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Resources and References

DeVeciana M et al. 1995. Postprandial vs preprandial blood glucose monitoring in women with GDM requiring insulin therapy. NEJM. 333:1237.

Langer O et al. 1994. Intensivied vs conventional management of gestational diabetes. Am J Obstet. Gynecol. 170:1036.

Saade G. 2005. GDDM: a pill or a shot? Obstet. Gynecol. 105:456.

Sheffield JS et al. 2002. Maternal DM and infant malformations. Obstet. Gynecol. 100:925.

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Topic Development

authors: David LaPierre


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