Gestational Diabetes in Twin Pregnancies – A Pathology Requiring Treatment or a Benign Physiologic Adaptation?

There is level-1 evidence that screening and treating gestational diabetes (GDM) in singleton pregnancies reduces maternal and neonatal morbidity. However, similar data for GDM in twin pregnancies are currently lacking. Consequently, the current approach for the diagnosis and management of GDM in twin pregnancies is based on the same diagnostic criteria and glycemic targets used in singleton pregnancies. However, twin pregnancies have unique physiologic characteristics, and many of the typical GDM-related complications are less relevant for twin pregnancies. These differences raise the question of whether the greater increase in insulin resistance observed in twin pregnancies (which is often diagnosed as diet-treated GDM (GDMA1)) should be considered physiologic and potentially beneficial, in which case alternative criteria should be used for the diagnosis of GDM in twin pregnancies. In this review, we summarize the most up-to-date evidence on the epidemiology, pathophysiology, and clinical consequences of GDM in twin pregnancies and review available data on twin-specific screening and diagnostic criteria for GDM. While twin pregnancies are associated with a higher incidence of GDMA1, GDMA1 in twin pregnancies is less likely to be associated with adverse outcomes and accelerated fetal growth than singleton pregnancies, and may reduce the risk of fetal growth restriction. In addition, there is currently no evidence that treatment of GDMA1 in twin pregnancies improves outcomes, while preliminary data suggest that strict glycemic control in such cases might increase the risk of fetal growth restriction. Overall, these findings provide support to the hypothesis that the greater transient increase in insulin resistance observed in twin pregnancies is merely a physiologic exaggeration of the normal increase in insulin resistance observed in singleton pregnancies (that is meant to support two fetuses) rather than a pathology that requires treatment. These data illustrate the need to develop twin-specific screening and diagnostic criteria for GDM, to avoid overdiagnosis of GDM and reduce the risks associated with over-treatment of GDMA1 in twin pregnancies. While data on twin-specific screening and diagnostic criteria are presently scarce, preliminary data suggest that the optimal screening and diagnostic criteria in twin pregnancies are higher than those currently used in singleton pregnancies.