Review: Gestational Diabetes

You can't tell if she has it just by looking

You can’t tell if she has it just by looking

Ever heard of gestational diabetes?  It’s when a when a woman develops diabetes during pregnancy.  It usually goes away soon after the baby is born.  All pregnancies are characterized by some degree of insulin resistance and high insulin levels: they are necessary for the baby.  Nevertheless, healthy pregnant women run blood sugars 20% lower than when they are not pregnant.

In the U.S., gestational diabetes occurs in 5% of pregnancies, affecting more than 240,000 births annually.  Compared to caucasians, gestational diabetes mellitus (GDM) occurs more often in blacks, native Americans, Asians, and Latinos.

So What’s the Big Deal?

Numerous problems are associated with GDM, for both the mother and the baby:

  • dangerously high blood pressure (preeclampsia)
  • excessive amount of amniotic fluid (the baby in the uterus floats in this fluid)
  • delivery requiring an operation
  • early or premature delivery
  • death of the baby
  • birth trauma, such as broken bones or nerve injury
  • metabolic problems in the baby (low blood sugar, for example)
  • abnormally large baby (macrosomia, a major problem)

Diabetic ketoacidosis—a life-threatening complication of diabetes—is rare in GDM.

How Is GDM Diagnosed?  (section updated December 28, 2013)

Most women should undergo a screening test around the 24th to 28th week of pregnancy.  Screen earlier if undiagnosed type 2 diabetes is suspected or if risk factors for diabetes are present.  The American Diabetes Association (2014 guidelines) recommends either one of two screening tests.

  • “One-step test.” It’s a morning oral glucose tolerance test after at least eight hours of fasting. Fasting blood sugar is tested then he woman drinks 75 grams oral of glucose.  Blood sugar is tested again one and two hours later.  This blood sample is obtained by a needle in a vein, not by finger prick.  Gestational diabetes is diagnosed if any of the following apply: 1) fasting glucose is 92 mg/dl (5.1 mmol/l) or higher, 2) 0ne-hour level is 180 mg/dl (10.0 mmol/l) or higher, or 3) two-hour level is 153 mg/dl (8.5 mmol/l) or higher.
  • “Two-step test.” This is a nonfasting test with only one needle-stick. The woman drinks 50 grams of glucose; plasma glucose is tested one hour later. But if it’s over 140 mg/dl (10.0 mmol/l), that’s a flunk and a three-hour 100-gram oral glucose tolerance test in the fasting state must be done (step two). Gestational diabetes is present if the three-hour glucose is 140 mg/dl (7.8 mmol/l) or higher. Other experts say the diagnosis requires two or more of the following:
    • fasting blood sugar > 95 mg/dl (5.3 mmol/l)
    • 1-hour blood sugar > 180 mg/dl (10 mmol/l)
    • 2-hour blood sugar > 155 mg/dl (8.6 mmol/l)
    • 3-hour blood sugar > 140 mg/dl (7.8 mmol/l)

You’ll find that various expert panels have proposed different criteria for the diagnosis. The National Institutes of Health in the U.S. published their consensus statement in 2013

There’s no need for the screening test if a random blood sugar is over 200 mg/dl (11.1 mmol/l) or a fasting sugar is over 126 mg/dl: those numbers already define diabetes, assuming they are confirmed with a second high reading.  A random blood sugar over 200 mg/dl (11.1 mmol/l) should probably be repeated for confirmation.  Gestational diabetes can be diagnosed at the first prenatal visit if fasting blood sugar is 92 or over mg/dl (5.1 mmol/l or over) but under 126 mg/dl (7 mmol/l), or if hemoglobin A1c at the first prenatal visit is 6.5% or greater.

Women with diabetes in the first trimester have overt diabetes, not gestational diabetes.

What’s the Treatment for Gestational Diabetes?

Briefly: diet, exercise, blood glucose self-monitoring,  and insulin if needed.  The immediate goal is to achieve normal blood sugars.

A registered dietitian is involved in teaching diet modification.  The standard recommendation is to reduce carbohydrate consumption to 35-40% of total calories.  [By comparison, the standard American diet provides about 55% of calories as carbohydrates.]  Protein and fat are about 20% and 40%, respectively.  Total calorie recommendations are based on the mother’s ideal body weight.  Insulin resistance is greatest in the morning, so breakfast is small.  Complex carbohydrates are favored over simple sugars.  Most women will achieve normal glucose (blood sugar) levels with diet modification.

Moderate exercise also helps control blood sugars, partially by increasing sensitivity of body tissues to insulin.

How often should blood sugar be monitored by the mother?  Ideally, at least four times daily: fasting (on an empty stomach before breakfast) and one hour after the first bite of each meal.

Insulin therapy should be seriously considered when fasting glucose is over 90–95 mg/dl (5.0–5.3 mmol/l) or 1-hour-after-meal glucose is over 120-130 mg/dl (6.7–7.2 mmol/l).  Fifteen percent of mothers with GDM will need insulin injections.  If elevated fasting glucose is the only problem, NPH insulin before bedtime is prescribed.  If sugar levels one hour after meals are elevated, then use rapid-acting insulin aspart or insulin lispro just before meals.  In some cases, both NPH and rapid-acting insulin are both necessary.

Outside the U.S., glucose-lowering pills are sometimes used: glyburide and/or metformin most commonly.

What About After Delivery?

Having had gestational diabetes, the mother is at high risk of developing typical non-pregnant diabetes in the future. She should be screened for the development of diabetes and prediabetes at least every three years. Regular exercise and loss of excess weight decrease the risk substantially.

Steve Parker, M.D.

Sources: article on gestational diabetes, accessed March, 2010 and October, 2011.  American College of Obstetrics and Gynecology position paper published in 2001.  Diabetes Care, vol. 34, 2011: supplement 1: S62.  Blood sugar levels on the 3-hour 100-gram glucose tolerance test are from the Fourth International Workshop-Conference on Gestational Diabetes, published in 2000. For gestational diabetes diagnosis: American Diabetes Association’s Standards of Care in Diabetes – 2014.


Filed under Diabetes Complications, Prevention of T2 Diabetes

8 responses to “Review: Gestational Diabetes

  1. Just had to throw in that babies born to mothers with GDM are at greater risk for being overweight and having DM later in life also.

  2. Good points, Brenna.

    [If this is the Brenna I think it is, note that she has a food and nutrition blog, Eating Simple, which is in my blogroll:


  3. Diabetes when detected in pregnant women is known as type 2 gestational diabetes. This diabetes occurs in the second trimester or even as far as the third
    trimester. There are many factors responsible for the development of gestational diabetes such as age, size or family history. Along with gestational
    diabetes, high blood pressure is a common problem. It is very important to follow a gestational diet plan to prevent gestational diabetes. It is very much necessary to keep a watch on the amount of calories intake. For more details refer

  4. Not just exercise,but follow-up of a good diet.In take of plenty water.Have a cool state of mind,not nervous.Laugh alot

  5. Gestational diabetes affects the mother in late pregnancy and the baby too. Gestational diabetes is also called glucose intolerance of pregnancy.

  6. Praying Pilgrim

    I have a question…The blood glucose levels that you have listed above are the same ones that my doc gave me (I failed my 1 hour test and refused the 3 hour test). The doc is treating me as GDM. I went to see a nurtitionist, followed the diet for the first week and ran all low blood sugars (all lower than 109 after meals). In frustration, I ate my regular diet and discovered the my levels went up but not past 144. My question is, when I looked up normal blood glucoce for pregnant women the range given by the American Diabetes Association for Pregnant Women was as follows: 80-110 before meals and >155 2 hours after. The American College of Ob. & Gyn Committee on Practice gives the following: Fasting 105 or less, 110 or less before meals, 155 or less 1 hour after the start of the meal and 135 or less 2 hours after the start of meal. This is a 25-30 point difference…where are do you get the numbers for blood glucose you list and my doc seems to agree with?

    I am not trying to be rude, just trying to understand. This the only place I found on the web that matches the numbers my doc gave. Thank you for your time.

    • Hi, Praying Pilgrim. Valid question.

      The source for my blood sugar numbers above is, which I reviewed in 2010 and again today, and stand by my numbers. UpToDate is available only to paid subrcribers ($400/yr), but there is a free (I think) consumer-oriented portion you may want to check out. UpToDate is written mostly by medical school professors for other doctors. It’s updated much more often than textbooks. For instance, the experts who wrote the gestational diabetes article now favor the 75-gram, 2-hour glucose tolerance test over the 3-hour 100-gram test (the opposite of their position in 2010).

      The numbers for the 50-gram screening test I mention above are from an American College of Obstetrics and Gynecology position paper published in 2001.

      Upon review of the UpToDate GDM article today, I also learned that the experts there consider gestational diabetes to be present at the first prenatal visit if fasting blood sugar is 92 or over mg/dl (5.1 mmol/l or over) but under 126 mg/dl (7 mmol/l), or if hemoglobin A1c at the first prenatal visit is 6.5% or greater. These numbers were endorsed by in January, 2011, by the American Diabetes Association (see Diabetes Care, vol. 34, 2011: supplement 1: S62. I will go into my original post and make some changes.

      Regarding blood sugar levels on the 3-hour, 100-garm glucose tolerance test: they are from the Fourth International Workshop-Conference on Gestational Diabetes, published in 2000.

      Here’s a link to UpToDate’s gestational diabetes article for the general public, although I’m not sure it will work. You may have to register at the site:

      This is confusing, for sure. As the experts at UpToDate wrote, the definition of gestational diabetes is in flux.

      I hope this helps.