How Sweet It Isn’t

By Peter Galvin, MD

Gestational diabetes mellitus (GDM), which is elevated blood sugar levels (hyperglycemia) during pregnancy, is associated with an increased risk of adverse perinatal outcomes. It is also associated with an increased risk of type 2 diabetes (T2D) and cardiovascular disease, later in life, in both the mother and her child. In 2020, GDM occurred in nearly one in eight pregnancies in the U.S., with even higher rates among women with Native American or non-Hispanic Asian/Pacific heritage, obesity, and those aged 35 years or older at delivery. The age-standardized rate of GDM at first live birth has increased from 47.6 to 63.5 per 1000 live births in the U.S. from 2011 to 2019, with even further increases seen during the Covid-19 pandemic.

GDM should not be viewed as an isolated occurrence that disappears after giving birth. Far from it, GDM can have long-lasting negative outcomes for both the mother and her offspring. There is a continuous, blood-sugar-level association between GDM and adverse pregnancy outcomes, including cesarean delivery, preterm birth, hypertensive disorders of pregnancy (eclampsia and pre-eclampsia), and clinically relevant infant outcomes including large-for-gestational-age or birth weight >90th percentile, high bilirubin, low oxygenation (hypoxia), and the need for neonatal ICU. GDM must be diagnosed using a three-hour fasting glucose tolerance test. Hemoglobin A1c, used to diagnose and evaluate treatment for both type 1 and type 2 diabetes, cannot be used to diagnose GDM.

In order to reduce the risk of adverse events for both the mother and child, once GDM is diagnosed it must be immediately treated. First line treatment is diet and physical activity, but at least one in four women will need additional treatment. The preferred treatment is insulin, however metformin has been shown to be nearly as effective as insulin. Newer medications such as glucagon-like peptide-1 receptor agonists (i.e., Ozempic), which have the additional effect of weight loss and are used in the treatment of T2D and obesity, have been used, but since they are relatively new, their long-term effects are as yet unknown, as is their safety for use during breast feeding.

Up to half of pregnant women with GDM will develop prediabetes or T2D at some point after delivery. In fact, GDM is associated with a 10-fold higher lifetime risk of T2D. This association has been repeatedly demonstrated in study after study. The link between these two diseases likely represents the shared manifestation of pancreatic beta-cell dysfunction. These are the cells that produce insulin. Studies have also shown that the risk of developing T2D following GDM during pregnancy can be substantially reduced by lactation (breast feeding), weight loss, proper diet, exercise, and the use of medications to treat prediabetes. Observational studies have shown that a higher intensity and longer duration of lactation is associated with an even greater reduction in risk for T2D.

Women with a history of GDM should be screened for diabetes at least every one to three years for the rest of their life. Also, children and adults born to mothers who had GDM are at increased risk of T2D, obesity, cardiovascular disease, and hyperlipidemia and should be screened accordingly. Finally, women whose mothers had GDM are themselves at higher risk to develop it, should they become pregnant.

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