Diabetes in Pregnancy: Lower HbA1c Threshold Improves Detection

MedicalResearch.com Interview With:
Ruth C. E. Hughes
Department of Obstetrics and Gynecology
University of Otago, Christchurch Women’s Hospital
Christchurch, New Zealand

Medical Research: What are the main findings of the study?

Dr. Hughes: The increasing prevalence of undiagnosed type 2 diabetes in women of childbearing age was the main driver behind our study.  In clinical practice, we were finding that women with probable undiagnosed diabetes (and pre-diabetes) had already started developing pregnancy complications at the time they were diagnosed with gestational diabetes diagnosis in the late second trimester. It seemed logical to try to identify them in early pregnancy, with the idea that they might benefit from earlier intervention.  We thus explored the usefulness of first trimester HbA1c measurements to identify women with unrecognised pre-existing diabetes.

In our study, an HbA1c of 5.9% (41mmol/mol) was the optimal screening threshold for diabetes in early pregnancy.  We found that a threshold of 6.5% (48mmol/mol), which is endorsed by the World Health Organization and American Diabetes Association for diagnosing diabetes in pregnancy, would miss almost 50% of women with probable pre-existing diabetes.  Of great relevance, women with an early HbA1c of 5.9%-6.4% (41-46mmol/mol) had poorer pregnancy outcomes than those with an HbA1c <5.9% (<41mmol/mol), with a 2.5-3 fold higher relative risk of major congenital anomaly, preeclampsia, shoulder dystocia, and perinatal death.  These women were also more likely to deliver before 37 weeks gestation.

Medical Research: Were any of the findings unexpected?

Dr. Hughes: Not really, although the rates of adverse pregnancy outcomes in women with an HbA1c 5.9%-6.4% (41-46mmol/mol) who did not meet New Zealand diagnostic criteria for gestational diabetes (and were therefore untreated) were possibly higher than we expected.  It suggests that these HbA1c levels are clinically important and provides useful data for further studies to examine whether early intervention reduces these risks.

Medical Research: What should clinicians and patients take away from your report?

Dr. Hughes: Clinicians and patients should not find an early pregnancy HbA1c result below 6.5% (48mmol/mol) reassuring.  An early pregnancy HbA1c 5.9-6.5% (41-46mmol/mol) identifies a group of women who have a higher risk of adverse pregnancy outcomes, who may benefit from early referral and monitoring.

Medical Research: What recommendations do you have for future research as a result of this study?

Dr. Hughes: Our study was of a largely Caucasian population and confirmation of the results in studies of women from diverse ethnic backgrounds is required.  The next step is to investigate whether early pregnancy intervention can modify these risks.


An Early Pregnancy HbA1c ≥5.9% (41 mmol/mol) Is Optimal for Detecting Diabetes and Identifies Women at Increased Risk of Adverse Pregnancy Outcomes

Ruth C.E. Hughes, M. Peter Moore, Joanna E. Gullam, Khadeeja Mohamed, and Janet Rowan

Diabetes Care published ahead of print September 4, 2014, doi:10.2337/dc14-1312 1935-5548