Gestational diabetes mellitus is similar to T2DM,  except that is associated with pregnancy.  As such, it often resolves shortly before or after birth.  As the fetus grows, its demands for tissue growth causes a similar increased demand for both insulin and circulating nutrients.  In conjunction with hormones associated with pregnancy, the body’s cells can’t use its own insulin effectively causing a temporary insulin resistance. In fact, all pregnant women have some level of insulin resistance during late pregnancy, but not necessarily diagnosable gestational diabetes.  Thus, many of the mother’s symptoms overlap T2DM: hyperglycemia, polyuria, polydipsia (thirst), and polyphagia (hunger).

There is an association between gestational diabetes and pregnancy-induced high blood pressure (gestational hypertension). The mechanism is not well understood. However, if the mother already has diabetes-induced changes in microvasculature, the risk of developing gestational hypertension is greater.

The baby receives all of the mother’s nutrients and insulin. Because insulin is an anabolic hormone (ie builds tissues), babies of mothers with gestational diabetes will tend to be larger than average.  And because of the high amount of circulating insulin in utero, the baby may have sudden hypoglycemia upon birth as that insulin makes the tissues take up the circulating glucose even though maternal supply has been cut off.

Pregnancy is the biggest risk factor for gestational diabetes. However, if the mother has risk factors for T2DM as well, the  mother is more likely to develop gestational diabetes.

In Mother	In Baby
abnormally high blood sugar	Baby is likely to be large (>4kg or 9lb) causing a more difficult delivery
presence of sugar in urine	possible hypoglycemia during birth (due to excessive maternal insulin during fetal growth)
high blood pressure possible	baby is more likely to develop Type 2 diabetes later in life (tissues exposed to so much insulin in utero that insulin resistance may have begun)

Figure 7.5 Clinical manifestations of gestational diabetes

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