How to detect true gestational diabetes

Published in The Hindu on March 27, 2008

HBA1C test can tell if a woman has been a diabetic even before conception. HBA1C test should be done at first visit especially when GTT tests abnormal

The way pregnant women are tested for GDM makes it difficult to say with surety that the disease has indeed been developed only during pregnancy. Women who are already diabetic but become aware of their disease at the time of pregnancy cannot be classified as having gestational diabetes.

The limitation

The conventional way to detect GDM is through oral glucose tolerance tests (OGTT). But such testing has a limitation; it cannot tell if the woman is truly a GDM case or a diabetic even prior to conception.

Unlike the OGTT, the HBA1C test is equipped to tell if a woman has been a diabetic even before conception. This is because HBA1C provides the average concentration of blood glucose during the weeks previous to testing. So the HBA1C test when done at the time of first visit, especially when the OGTT value is abnormal, can help in distinguishing the true GDM cases from the other.

The paper published in the Diabetes Care journal last year by Dr. Balaji and others found that 33 of the 507 women tested had HBA1C above 6. This clearly showed that they (33 women) did not develop diabetes during pregnancy but were already diabetic (even before conception).

Dr. Balaji is a Consultant with the Chennai based Apollo Hospitals and the Dr. V. Seshiah Diabetes Care and Research Institute, Chennai.

Detecting women who are diabetic even before conception is very important as controlling their glucose level will help prevent foetal malformation and other problems. “Organogenesis takes place during the first 6-8 weeks of gestation. So early detection of such [diabetic] cases is very important,” said Dr. Balaji.

Only for diagnosis

“The HBA1C discussed in the paper is only for diagnosis and not for treatment,” he underlined.

But the paper brings out more important and interesting aspects.

Even when the HBA1C value was normal at the time of first screening (but the OGTT showed that their glucose level was not normal), a second group of 53 women developed the disease during the course of pregnancy. These 53 women are the true GDM cases.

“This brings out the importance of testing [for GDM] every month even when HBA1C value is below 6 at the time of first testing,” Dr. Balaji said.

The study showed that the glucose level (as seen in OGGT and HBA1C tests) in some women follow a confusing pattern.

It showed that at times the HBA1C may take time to manifest the gestational diabetes condition. So banking on the first visit result alone would have missed out these cases.

Normal women

Finally, studying the fourth group of 159 women helped bring out the importance of knowing the truly normal women. It helped knowing that a HBA1C level less than 5.3 would not develop gestational diabetes during the entire course of pregnancy.

But some women (23) with values between 5.3 and 6 developed gestational diabetes during subsequent visits.

“Women with normal OGTTs but HBA1C above 6 and women with HBA1C between 5.3 and 6 require utmost attention,” notes the paper.