Carb-Loading Before 3-Hour Glucose Tolerance Test?

Updated on September 27, 2012
J.L. asks from Portland, OR
16 answers

I found out that I failed my 1-hour GTT (143) and need to do the 3-hour GTT. This is my second pregnancy. During my first pregnancy, I also failed my 1hr but passed my 3hr GTT. I'm still worried though. I also found out something new. I need to follow a high-carb diet for three days prior to my 3hr GTT...something I wasn't told to do during my last pregnancy. I remember my old OB told me to just eat normally except no eating after 8pm the night before my test. I'm just a little uncomfortable with carb-loading. I don't normally eat a high-carb diet but not a low-carb diet either. Too much carbs makes me feel nauseous. The nurse I talked to said if I don't follow the diet I might fail the 3hr GTT since that's standard procedure.

I was normal size before pregnancy (121 at 5'0") and I've gained a normal amount of weight thus far (now 138).

Thoughts and opinions?

Thank you so much for all the advice and response. I apologize that carb-loading is probably not the most accurate word to use in this case. The diet actually recommends one additional serving to the "normal" serving of carb that an individual should eat. However, that IS carb-loading for me...that would mean I have to eat at least 4x the amount of carbs I normally eat. I think the doctors/nurses/etc should consider that each individual is different which I think is the biggest variable that affect the result of the GTT. I'm not going to stuff myself with carbs and make myself sick. That wasn't how I passed my 3-hour GTT during my previous pregnancy. Thank you everyone for the reassurance and advice. Wish me luck!

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So What Happened?

I passed! All four were within normal limits; the nurse said I would be allowed two elevated results before deemed diabetic. I just ate my normal diet (relatively low starch, plenty of veggies and some fruits, and moderate protein) -- didn't follow the diet they gave me. Then I fasted for 12 hours before the test.

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answers from Jacksonville on

Where are you having the testing done? When I had mine done years ago (yeah... I had to have the 2nd one also)... I didn't do it at the doctor's office. I had to go to the lab. If you know the lab, call THEM and Ask THEM what the proper instructions are for the test.

That is what I would do.

5 moms found this helpful

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answers from Santa Barbara on

Victoria is right on! If you have the lab slip, call them. I work for a national testing lab (in women's health) and have never seen that directive.

The fasting is also 8 hours before the test, not necessarily 8 pm.

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answers from Dover on

I had to have the 3 hr test with both pregnancies (failed 1 hr test both times). Passed the 3 hr the first time but not the second...but I was 15 years older the second time. Neither time was I told to fact, I have never heard of this before. Carbs turn straight to sugar so it seems odd to me.

4 moms found this helpful


answers from Minneapolis on

This seems wrong. It would seem to increase your chances of failing the test, since carbs turn to sugar. I agree that calling the lab and asking them would be a good idea.

I was NOT told to do anything but eat normally the day before the test and I did pass.

3 moms found this helpful


answers from San Francisco on

I had to have the 3 hr with both my girls and we told to eat normal and to watch my carbs. I passed with both. I would call the doc or the lab and double check because that sounds a little strange.

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answers from Los Angeles on

I ate protein before my three hour and blame granola for causing me to fail my one hour. Why you would carb load make no sense to me, seems like it would cause you to fail again.

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answers from Jacksonville on

With my first, I failed both my 1 and 3 hr test and was diagnosed with GD. With my second, I passed my 1 hr test, no GD (which, apparently, is weird because if you have GD the first pregnancy you have a 80%+ chance of having it with your second).

For my first, my OB mentioned that I shouldn't restrict carbs in my diet (maybe some women try and restrict them in order to pass the test?) and have a little extra carbs for a few days prior. I think he actually said, indulge yourself and have a candy bar after dinner for a few days (no, really!).

For my second, I did NOT do the extra carbs and passed.

I really think that it's just up to your body type/metabolism. I'm not 100% sure I really had GD with my first pregnancy. Sure, my blood sugar fell within the 'range' for GD during the test, but I think I'm just slow to process carbs. One of the big concerns of GD is having a large baby, and my full term kiddo was only 6lbs 7 oz!

That being said, please don't try to "rig" your eating just to pass the test. if you do in fact have a great likelihood for GD, you want to make sure you and your baby are being treated for it. All I ended up doing was monitoring my blood sugar and restricting my carbs a bit. Definitely not a big deal....

1 mom found this helpful


answers from New York on

I was told to eat normally and not fast at all. I passed the first test. I have had 2 friends fail the first test and they were not told to "carbo Load". Call your doctor.

1 mom found this helpful


answers from Chicago on

This does not sound right. And it sounds downright unhealthy to follow a high carb diet for three days while pregnant. Definitely call your OB to make sure this is what they want you to do. Good luck!

1 mom found this helpful


answers from Columbus on

In my opinion, carb loading would be a sure way to fail the test! I was told by my doctor I could eat right up to the 1-hour test, and of course I failed. So for my second pregnancy, they said I could eat and I fasted. When I went in, I told the phlebotomist and she said of course you're supposed to fast and they would never tell anyone to eat. Suffice it to say, I passed the second time around.

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answers from Washington DC on

I'm a phlebotomist and I can tell you that eating normally then fasting for 12 hours before the test is the best way to go.

The purpose of the 3 hour test is to monitor you from start to finish with NO OTHER SUGARS in your system (hence the 12 hour fast). You are given a very specific amount of sugar and there are standard time frames that the sugar should be metabolized in your system.

Here's the steps to take for the test:
1. eat normally up to 12 hours before the test (most people schedule/go in for their test early in the morning so they are sleeping through most of the 12 hours).
2. 12 hours before the test stop eating
3. In that 12 hours it's best to drink only water. They keep going back and forth on whether it's ok to have black coffee or not, it has yet be to fully determine if it affects your blood sugar. HOWEVER, it DOES affect your hydration level since it's a diuretic because of the caffeine. And when you're going to have your blood drawn 4 times in a short time period ... I'd avoid anything that is going to shrink your veins and make them harder to hit.
4. Once you get to the lab they will give you instructions on what to do. But generally the schpeel they give goes like this, they take the first draw BEFORE you drink the glucose, once you drink the glucose they'll have you come back every hour to draw your blood. you will need to have your blood drawn within about 10 minutes of the original time they drew your blood. They will tell you not to eat or drink anything besides water (some places will ok black coffee) and to stay either in the lab, in the hospital or on the grounds of the facility. This is to safeguard in case of fainting or dizzyness or such.

So to sum up ... eat normally, fast 12 hours before the test with only water, follow the directions at the lab and take a good book or some magazines with you :) adding extra water to your fluid intake a couple days before the test wouldn't be a bad idea either.

1 mom found this helpful


answers from Austin on

I've never heard of that..... it has been many years since I had to do the 3 hour glucose test, but I also failed my 1 hour tests (both times), but passed the 3 hour tests.

(I had to take the test twice during my last pregnancy..... once at 3 months, and again at 6 months.... I had 2 factors against me.... I was "older" (34 at the time), and I also had a parent with insulin dependent diabetes, so I had to go through the screening, also. This was during 1991.... see, I told you it had been a while since I took the glucose tests!)

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answers from Portland on

NO, NO, NO!!! Don't do a high carb before a GTT! The nurse who told you that is an idiot! Following a high carb will definitely make you fail the GTT. Carbs turn into sugar which will raise your glucose number, not lower it! Not only that, too many simple carbohydrates will cause your body to increase insulin production to digest, which causes weight gain. I would follow your regular eating habits, and if you need to increase anything, increase protein intake. Having been there myself when I was pregnant with my first child, I gained 10 pounds in one month (all other weight gain was normal) but I was sent in for a GTT, too, and found out I had gestational diabetes. That weight gain was AFTER I had a dietician tell me to eat more carbs for the baby's sake, and less protein & fat...which I did, and it was detrimental to my health, as well as my baby's. So don't listen to that BS!!


answers from Hartford on

Uh, no... who told you that? The flobotomist is the lab? I would do what your OB said: Don't "carb load." Eat normally and healthfully and then do the appropriate fasting.



answers from Portland on

are they trying to find out if you have gestational diabetes? I am not sure why lots of carbs because too much carbs turns into sugar and causes people with diabetes to have a high count.

Anyway, gestational diabetes is usually caused by not enough D3 so have them check that through a blood test. Or go down and get some and take it just before your diabetes test and also have them check the D3. Doctors are usually unaware of this but there are studies out there to show that D3 is needed. You can usually take 3,000 to 5,000 IUs per day but again everyone is different so PLEASE make sure you get a blood test to have this checked out.




answers from Washington DC on

If you've ever read any of my other responses on pregnancy you know that I have a blood clotting disorder that required close monitoring throughout my pregnancies. I have a team of OB's and Perinatologists from The Advanced Fetal Care Center @ University of Maryland and Johns Hopkins that I saw on a weekly basis throughout my pregnancies. I had weekly sonograms and fetal monitoring 3 times per week. I'm telling you all of this because I want you to know I was very blessed to have the best of the best caring for me and our girls.

I failed the 1 hr with both of my girls. I passed the 3 hour with my first but had gestational diabetes with my second one. If I recall I was instructed to eat normally with the one hour test but I too was told to eat more carbs for 3 days prior to the tolerance test.

I don't think the words carb load were ever used but they said if you eat a healthy balanced diet then just eat 1 extra piece of toast with breakfast, extra helping of pasta for lunch or dinner for the 3 days prior to the test. But I was to fast for 12 hours not 8 on the 3 hour tolerance test. I'm not sure if this makes a difference or not but both of my parents were insulin dependent type 2 diabetics before they passed away. Perhaps they wanted to check my levels in a worst case scenario.

I would absolutely follow up with a phone call to your OB to clarify the instructions. You don't want to mess this up and have to do the test over again.

Peace and Blessings,
T. B

*****edited to add, I just googled "3 hour glucose test" and this is one of the links that came up.

You are in fact as I said, to eat more carbs for 3 days prior to testing.

Peace and blessings and I will pray that your test comes back normal :)

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