Gestational diabetes in someone who is lean
Typically we think of Gestational Diabetes (GDM) as due to an imperfect pancreas that cannot cope with the extra insulin needed in pregnancy. This need is there because the hormones from the placenta cause insulin resistance so one needs extra insulin just to keep the same glucose. The insulin resistance is worse if there is obesity present or the mom gains excess weight so that even more insulin is needed. The defect in the pancreas is poorly understood but almost certainly sets the stage for the later Type 2 diabetes that women who had gestational diabetes are more prone to develop.
Thus we often see gestational diabetes:
Developing at about 26-28 weeks when the placental hormones are really rising.
In someone overweight or who gained too much weight (See Blog of July 11) contributing to the insulin resistance.
With a positive family history suggesting they inherited an imperfect pancreas.
In someone older because our pancreas works less well as we age.
But what about if someone is lean, has not gained too much weight, what is going on for them to have GDM. I recently saw a 26 year old woman who at the start of pregnancy was 105 lbs and 5’ 8”, she was super fit and had who gained 12 lbs. Now at 27 weeks has been diagnosed with GDM. What goes through my mind when I assess someone with GDM is how much is the problem insulin resistance and how much is insulin deficiency- both are always present but usually one is more dominant.
A few women like this may actually be developing Type 1 diabetes and they may have antibodies to their insulin producing cells (islets) in their blood but we do not routinely check for these. If it is Type 1, the diabetes will declare itself soon enough and have symptoms such as thirst or going to the bathroom at night. Either way as of now we have no intervention that works. A few of these women may have an unusual form of type 2 diabetes called Maturity onset Diabetes of the young (MODY) but more of this in another blog.
For the most part I see this person who is lean, fit as having much more of a problem with their pancreas than insulin resistance. As such they are more likely to need insulin during the pregnancy, there simply is often not much further improvement to be made in terms of diet changes. More importantly after the baby is born it is very important for this woman to be tested to see if the diabetes has gone away and her sugar should be checked yearly and before any future pregnancy.