What is the pathogenesis of gestational diabetes mellitus (GDM) in normal pregnancies?

Updated: Apr 29, 2020
  • Author: Thomas R Moore, MD; Chief Editor: George T Griffing, MD  more...
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Answer

Answer

In the pregnant woman, each meal sets in motion a complex series of hormonal actions, including a rise in blood glucose and the secondary secretion of pancreatic insulin, glucagon, somatomedins, and adrenal catecholamines. These adjustments ensure that an ample, but not excessive, supply of glucose is available to the mother and fetus.

Compared with nonpregnant subjects, pregnant women tend to develop hypoglycemia (plasma glucose mean = 65-75 mg/dL) between meals and during sleep. This occurs because the fetus continues to draw glucose across the placenta from the maternal bloodstream, even during periods of fasting. Interprandial hypoglycemia becomes increasingly marked as pregnancy progresses and the glucose demand of the fetus increases.

Levels of placental steroid and peptide hormones (eg, estrogens, progesterone, and chorionic somatomammotropin) rise linearly throughout the second and third trimesters. Because these hormones confer increasing tissue insulin resistance as their levels rise, the demand for increased insulin secretion with feeding escalates progressively during pregnancy. By the third trimester, 24-hour mean insulin levels are 50% higher than in the nonpregnant state.


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