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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 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 blod 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 lackluster. This is actually not making
enough insulin at all. When there isn't enough insulin to bring 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. But even with this doubled risk, the chances of having a
baby with congenital abnormalities is only 4 to 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.
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