Develops during pregnancy and is usually diagnosed at 24 to 28 weeks of gestation on the basis of elevated plasma glucose levels on glucose tolerance testing.
Goal of therapy is to achieve maternal glucose levels that are as close to normal as possible in order to avoid fetal macrosomia and complications.
Initial therapy for gestational diabetes is usually dietary modification. Insulin is started when acceptable glucose levels cannot be maintained with diet alone.
Maternal postnatal testing for diabetes or impaired glucose tolerance is performed at least 6 weeks following delivery.
The risk for recurrence of GDM in subsequent pregnancies or progression to type 2 diabetes is high.
Gestational diabetes mellitus (GDM) has traditionally been defined as any degree of glucose intolerance with onset or first recognition during pregnancy. However, the criteria for diagnosis are controversial,  and some authorities now define it as diabetes diagnosed in the second or third trimester of pregnancy that is clearly not overt diabetes.  It is usually recognised at 24 to 28 weeks of gestation on the basis of abnormal glucose tolerance testing. 
Professor of Medicine
Harvard Medical School
Director of Clinical Research
Endocrinology, Diabetes and Hypertension Division
Brigham & Women's Hospital
EWS declares that she has no competing interests.
Department of Obstetrics, Gynecology and Reproductive Biology
Harvard Medical School
Diabetes in Pregnancy Program
Brigham and Women’s Hospital
CZ declares that she has no competing interests.
Dr Ellen W. Seely and Dr Chloe Zera would like to gratefully acknowledge Dr Jeremy Soule and Dr Leonard E. Egede, previous contributors to this monograph. JS has undertaken research support and speakers' bureau activity for Novartis, Bristol Myers Squibb, Astra Zeneca, and Sanofi-Aventis. LEE is an author of a number of references cited in this monograph.
Instructor in Medicine
Brigham and Women's Hospital
Division of Endocrinology
Diabetes and Hypertension
RKG declares that he has no competing interests.
Department of Family Medicine
University of North Carolina
Assistant Program Director
MAHEC Rural Family Medicine Residency
WM declares that he has no competing interests.
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