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Pre-gestational Diabetes Diagnosed in Early Pregnancy

6/1/2015 - Tiffany A. Moore Simas, MD

Mentor: Pamela D. Berens, MD

Editor:  Roger P. Smith, MD

Diabetes mellitus complicates approximately 6-7% of pregnancies, with roughly 90% due to gestational diabetes mellitus (GDM) and 10% due to existing Type 1 or 2 Diabetes (DM). 

Defined as carbohydrate intolerance with onset or first recognition in pregnancy, ACOG recommends screening all non-pregestational diabetic women for GDM between 24 and 28 weeks.  GDM risk increases with advancing pregnancy; insulin resistance is greatest in the third trimester.  Some women demonstrate elevated fasting glucose or glucosuria and merit immediate further evaluation.  Additionally, women with risk factors such as GDM or macrosomia in a previous pregnancy, obesity, known impaired glucose metabolism, and a family history of DM merit early pregnancy screening for undiagnosed DM. 

Screening tests commonly performed early in pregnancy to confirm pre-gestational diabetes include:  fasting plasma glucose (FPG); two-hour 75 gram oral glucose tolerance test (2hOGTT); glycosylated hemoglobin (A1c); and a one hour 50 gram oral glucose tolerance test usually used later in pregnancy for GDM screening, confirmed with the standard three hour 100 gram glucose tolerance test unless the 50 gram test was markedly abnormal.  Administering a glucose load to a patient with suspected diabetes may precipitate diabetic ketoacidosis (DKA) or a hyperglycemic hyperosmolar non-ketotic (HONK) state and should be avoided when there is concern for hyperglycemia.  FPG and A1c values are adequate to diagnose diabetes if the FPG is ≥126 mg/dL or the A1c is ≥6.5%.  Normal values for FPG are ≤100 mg/dL and for A1c are ≤5.7%. Intermediate levels are indicative of increased risk and require further monitoring.

If pre-gestational diabetes is diagnosed, additional evaluation and management considerations are needed.  More frequent prenatal visits are indicated to achieve optimal glucose control through diet, exercise and possibly medication.  Various monitoring regimes are acceptable using therapeutic blood sugar goals (fasting levels ≤ 95mg/dL, premeal ≤ 100mg/dL, 1h postprandial ≤ 140mg/dL, 2h postprandial ≤ 120mg/dL, and night time values not ≤ 60mg/dL; or a target of a A1c ≤6%).  Urine ketones should be assessed when blood sugars exceed 200 mg/dL. 

Blood sugar and A1c goals are usually achieved with a combination of oral agents or long and rapid-acting insulins or insulin pumps.  Rapid-acting insulins are administered with meals.  Long-acting insulins are often administered once or twice daily depending on the specific type used.  Medication requirements will likely increase during pregnancy.

Pregnancy can exacerbate many diabetes-related complications, and diabetes is associated with obstetric-specific complications.  Women with pre-gestational diabetes should ideally have a preconception evaluation or the following in early pregnancy: 

  • Eye exam for retinopathy
  • Creatinine and urine protein for establishing a baseline
  • EKG
  • Thyroid function studies

Because pregnancies complicated by pre-gestational diabetes are at high risk for perinatal morbidity and mortality, especially with elevated A1c, good dating should be established with early ultrasonography followed by a comprehensive ultrasonographic exam for fetal anomalies and a fetal echocardiogram.  Antepartum fetal testing should be initiated between 32-34 weeks or sooner when appropriate.  Timing of delivery is dependent on many factors, but expectant management beyond the estimated due date is not recommended.  Blood sugars must be monitored and insulin managed during labor and delivery to minimize the risk of fetal hypoglycemia.

Further Reading:

ACOG Practice Bulletin #137:  Gestational Diabetes Mellitus, August 2013

ACOG Practice Bulletin #60:  Pregestational Diabetes Mellitus, March 2005

Initial approval 2/2015;  Reaffirmed 7/2016


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