All women should be screened for gestational diabetes mellitus during pregnancy. Gestational diabetes can cause complications for mom and/or baby, but there aren’t always noticeable symptoms. Therefore, it could go undetected if doctors only tested those who show symptoms. For this reason, glucose screenings are done in all pregnancies. Let’s take a look at what to expect from a pregnancy glucose screening.
Pregnancy Glucose Screening: Why and When
As we discussed in our Gestational Diabetes post, some pregnant women develop a type of diabetes that wasn’t there before pregnancy and goes away after. While there are some factors that increase a person’s chance of developing gestational diabetes, it can happen to anyone. And as mentioned above, there often aren’t any signs or symptoms. So in order to be sure that your blood glucose (sugar) isn’t running too high, you’ll have at least one test. The detection of high glucose on one test doesn’t necessarily mean that you have gestational diabetes, but it indicates that further testing is warranted.
Most healthcare providers follow the guidelines of screening women around the end of the second trimester, between the twenty-fourth and twenty-eighth week of pregnancy (1). You may be tested earlier than this if you have any of the risk factors for gestational diabetes.
Risk factors for gestational diabetes include:
- Having had gestational diabetes in an earlier pregnancy
- Family history of diabetes
- Having any medical condition that increases risk of diabetes, like PCOS or metabolic syndrome (2)
There are two main glucose tests that may be used to screen for the possibility of gestational diabetes or to confirm the diagnosis. In each, glucose will be introduced into your body. After a period of waiting, your blood will be drawn to see how much glucose remains in your blood. This allows your provider to see how well your body is able to handle the sugar. Let’s take a look at each of the tests.
Glucose Screening Test
Also called the glucose challenge test or glucose challenge screening test, this is the test that nearly all pregnant women have. As mentioned above, it is performed between the 24th and 28th week of pregnancy, though it may be earlier if you’re at higher risk for gestational diabetes.
On the day of the test, you will go to either your doctor’s office or a lab. They may first draw your blood to get a baseline number, although this step is less common. You’ll be given a sugary drink that is similar to an overly-sweetened soda, and you’ll be asked to drink it within five minutes. After that, you’ll simply sit and wait for an hour. At the end of that wait, your blood is drawn again and a sample is sent to a lab. You should receive your results within a few days. If your blood glucose is under a certain number (usually 140 mg/dL), you won’t need to do anything further.
Oral Glucose Tolerance Test (OGTT)
If your blood glucose is too high on your pregnancy glucose screening, you will need to have another test, the oral glucose tolerance test. This test is similar to the other one but is more detailed. First, you’ll be told to fast before the test. Your doctor will give you more details, but most say that you can’t eat for at least eight hours before the test. Some doctors advise fasting for as many as fourteen hours before testing (3). Don’t worry. They do these tests in the morning, so you won’t be starving all day.
Next, they will draw blood to get a fasting number. Then, just as with the first test, you’ll need to drink a sugary liquid. But this time, they’ll draw your blood several times. It will be drawn at one hour, again at two hours, and finally at three hours after finishing the drink. Plan to bring a book or something to help pass the time as you wait. As with the one-hour test, you should get results from your three-hour test within a few days.
In addition to the two blood tests, some doctors check for sugar in your urine. (Sugar in the urine is called glucosuria.) If you have too much sugar in your system, some of it is lost in your urine. It’s not uncommon to have some sugar in your urine, especially during the second and third trimesters, but if the numbers are too high, it tells your doctor that further testing is necessary (5).
What If My Test Numbers Are Too High?
Your doctor will know how to interpret your results, and can explain to you what they’re looking for. The values below are based on the most common test, which has the pregnant woman drink 100 grams of glucose. Some tests are based on a different amount of glucose in the drink, so the values they’re aiming for may vary.
With the glucose screening test, or the one-hour test, your doctor will want to see that your blood glucose has dropped below 140 mg/dL (1). If your number is higher than that, it doesn’t necessarily mean that you have gestational diabetes, but it does mean that you’ll need to do the more in-depth OGTT.
On the oral glucose tolerance test, abnormal values are:
Fasting: greater than 95 mg/dL
1 hour: greater than 180 mg/dL
2 hour: greater than 155 mg/dL
3 hour: greater than 140 mg/dL (4)
If your blood glucose is too high on only one of the readings, your doctor may just want to test again in a few weeks. In the meantime, they may suggest some changes to your diet.
If two or more of the readings are too high, you will be diagnosed with gestational diabetes. Your doctor or midwife will work with you on a treatment plan. You will likely see a dietician about modifying your diet, will be taught how to monitor your blood sugar at home, and will learn how to use oral medication or insulin if necessary. If you’d like to read more about the glucose tests, there’s a great resource here.
What Is The Pregnancy Glucose Screening Like? Will It Hurt?
How uncomfortable you find the tests to be depends on your general tolerance for needles and blood draws. The tests really are as simple as outlined above. You just drink, sit, and have your blood drawn. Some women describe it as uncomfortable or scary, especially if they’re sensitive to needles and blood. Most women don’t find it to be a big deal.
Aside from actually having your blood drawn, the other thing you might experience is a bit of light-headedness. Drinking sugar on an empty stomach makes some people feel nauseous. And some women may feel a little lightheaded before the test since they’ve had to fast. Ideally, plan to have someone drive you in case you do feel bad on the drive there, or after you’ve consumed all of that sugar.
The bottom line is that these tests are at most a little uncomfortable. Yet, most women will get a good result on the first test and then move on. For those who do need to take both tests, and those whose numbers fall outside the desired ranges, we can at least be thankful that these tests are available so that you can work to control your glucose levels and get your little one here safely!
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- Tests & diagnosis for gestational diabetes. (2017, May 01). https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes/gestational/tests-diagnosis
- Glucose tolerance test. (2020, March 06). https://www.mayoclinic.org/tests-procedures/glucose-tolerance-test/about/pac-20394296
- Glucose tolerence test. (2020, August 27). https://americanpregnancy.org/healthy-pregnancy/pregnancy-health-wellness/glucose-tolerence-test-757/
- Glucose screening tests during Pregnancy: Medlineplus medical encyclopedia. (n.d.). https://medlineplus.gov/ency/article/007562.htm
- Glade, B.C., Schuler, J. (2011). Your Pregnancy Week by Week, 7th edition. First Da Capo Press.