Diabetes in Pregnancy

December 14, 2007

Just as in hypertension in pregnancy, where there are two types--hypertension coincidental with pregnancy and hypertension because of pregnancy (PIH), there are two types of diabetes that can be present in pregnancy:  Gestational Diabetes and Insulin Dependent Diabetes Mellitus (IDDM).  There is also a combination of the two in which IDDM is just harder to control because of a gestational diabetes overlay.

Gestational Diabetes

Pregnancy causes a phenomenon called "insulin resistance," which for lack of a better explanation means that a pregnant woman makes insulin--it's just that it's lousier insulin.  It doesn't react to receptors at the cellular level as well, meaning it takes more of it to do what insulin is supposed to do--bring sugar into the cells for energy.

Being overweight makes this worse.  In pregnancy, when the insulin made just can't do the job anymore, we call this GDM (Gestational Diabetes Mellitus).  Since the insulin isn't as powerful, a diet low in sugar and carbohydrates will mean less sugar in the system; less sugar in the system means less left over from the faulty insulin chemistry.  This is what is meant by diet-controlled gestational diabetes and actually works fairly well with this condition.

Because diet does work well, very few women need insulin injections with GDM.  As many as 1 out of 10 - 20 pregnancies will have GDM.  It used to be a sneaky disease until we started screening all pregnancies with the O'Sullivan test (a 1-hour blood glucose determination after a sugar drink).  Out of those with an abnormal test, a full 3-hour glucose tolerance test (a fasting, followed by 3 subsequent sugar determinations after a sugar drink) will then pick out the real GDM patients.  GDM can have the same complication as "regular" diabetes--large babies, so it is important to manage it aggressively.

And then there are the "real" diabetics.

Diabetes Mellitus

This isn't making insulin that is lackluster, but actually not making enough insulin at all.  When there isn't enough insulin tobring sugar from the blood stream (your blood stream is what you eat) into the tissue, it builds up in the blood stream, gunking up the works.  This leads to damage of the blood supply to one's organs, resulting in kidney damage, eye damage, etc.

Women who are diabetic when they conceive are at twice the risk for abnormal fetuses, even when their blood sugars are well controlled with a high tech continuous blood glucose monitor. (But even with this doubled risk, the chances of having a baby with congenital abnormalities is only 4 -5 out of a hundred.)

But diabetic women who have blood sugars that aren't well controlled have a staggering increase in their risk--by about ten times what their normal risk would be for a well-controlled diabetic state.  So the real deal-breaker here is good control before conception. 

Luckily, there's a test that can tell how well the diabetes has been controlled.  It is called a HbA1c (Hemoglobin A1C) and measures how much sugar is "stuck" to a certain hemoglobin molecule.  The beauty of this relationship between hemoglobin and glucose is that it's a firm interaction--meaning that it reflects how well the diabetes has been in control for a long time, usually months.

So a normal HbA1c in the first trimester will be a very reassuring test for a pregnant diabetic patient.  And the risk of congenital abnormalities and miscarriage is directly related to how abnormally high the HbA1c is.  This makes it, besides the serum glucose measurement, the most important prenatal (and preconception!) test in diabetic pregnancy.

But even with good control preconception and during the first trimester, the two natural enemies, pregnancy and diabetes, begin to fight it out. The very thing that can cause that normal variation known as GDM can make insulin-dependent diabetes harder to manage, too, by driving up the insulin needs.  This means that no "set" dosage of insulin can be established with expectations of the pregnancy sugar control to be on automatic pilot.  It doesn't work that way, and pregnancy + diabetes is usually a continuing medical challenge always at red alert.

Large babies make for more difficult vaginal deliveries.  Besides the risk of cephalopelvic dysproportion (baby's to big to fit out), and shoulder dystocia (head delivers but shoulders get stuck), there is also increased risk of placental abruption premature separation.  Since the C-section rate is higher in diabetic patients for all of the above reasons, it's important to know that Cesarean delivery is not the perfect answer to a pregnant diabetic's problems.  Diabetic women don't heal well after surgery and their chances of infection are much greater.

In spite of all of these concerns, a woman whose sugars are well controlled can stack the deck in her favor, especially if she is evaluated preconception.  But diabetes is a definite problem in pregnancy that requires diligence on the part of the obstetrician and strict compliance on the part of the patient.

'My baby is large on ultrasound for the gestational age. My one-hour glucola test came back elevated. Is this diabetes?"

Certainly LGA (large for gestational age) babies are a concern and make us think of gestational diabetes. The one-hour glucola test (the O'Sullivan test) is the screen for it. But because it's just a screen, it's only considered valid (and reassuring) if it comes back normal.

If it's elevated, we chunk the results and move up to a better diagnostic test -- the full-blown Glucose Tolerance Test (GTT), where you have a fasting sugar drawn, then you consume a sugar load (possibly more glucola), then have blood sugars drawn at one, two and three-hour intervals. There are blood sugar levels appropriate for each blood sample in this test, and if you are too high in two of them, you will be considered a gestational diabetic (up to 10 percent of pregnant women can be).

Even if this happens, don't panic. It is usually controlled with a diabetic diet -- a diet with a lot of food on it, actually, but with just a shift in the types of things you eat. Rarely do we need insulin. Gestational diabetes is not a real diabetes,  because it's not that you don't make enough insulin, it's just that the insulin you make is not as good. We call this "insulin resistance." But don't underestimate gestational diabetes -- it can cause bad effects on the baby and you just like the real thing! Like...

Humongous babies that are at a higher risk for complications of delivery like shoulder dystocia, and...more likelihood of you needing a C-section.  But if you were to have gestational diabetes and were to be real good about your diet, you will likely avoid these complications. Your doctor will watch for these concerns. But we're getting ahead of ourselves. You  only flunked the one-hour test. You may very well pass the GTT with flying colors, in which case you're off the hook.

By the way, the woman who instituted the glucola test -- a test that has probably saved thousands of lives by making often-silent gestational diabetes another aspect of pregnancy to be treated -- Dr. O'Sullivan herself -- was one of my examiners on my board exams. And she didn't ask me one single question about diabetes!

"How low should your blood sugar be when you have gestational diabetes, and how does a doctor make this diagnosis?"

The protocol I use in my practice is if the O'Sullivan (glucola screen) test is abnormal at 24 to 26 weeks, I then move up to the three-hour glucose tolerance test. If two out of the four blood samples are abnormal, that's when I make the diagnosis of gestational diabetes. If your doctor labeled you as gestational diabetic on the glucola screen alone, he or she may be using this technique to justify an ADA diet (American Diabetes Association). It's jumping the gun, but there's no real harm here, especially if you're continuing to test your sugars.

Even if you were on such a diet and not even diabetic, it's a nice diet for any pregnant woman, because there isn't inappropriate weight gain on this diet. (It's not unlike the "Sugar-buster Diet" my colleagues in New Orleans have developed.)

If foregoing the full glucose tolerance test was a mistake, you'll see evidence of this on the blood sugars you've been taking. (Perhaps your doctor was being sensitive to not putting you through a major  pain-in-the-behind test.)

How low is too low? A sugar so low that you're dizzy, pass out, or become ill is too low. If there are no deleterious effects, a low blood sugar is not harmful to you or your baby. (The baby takes all of the sugar it can and leaves the rest for you.)

Even if symptoms of diabetes are present, they are often not recognised or are attributed to 'being busy' or 'getting older.'

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