Testing for Diabetes in Pregnancy: What do we know?

Diabetes is not uncommon in pregnant women.

There are two categories of diabetes in pregnant women,

  • Diabetes that is already present before pregnancy (a woman with diabetes becomes pregnant)  and
  • Diabetes that develops in a woman during the course of pregnancy or after she becomes pregnant (gestational diabetes mellitus or GDM) and may subside after childbirth.

Why is it important to identify GDM?

GDM may lead to adverse outcomes in pregnancy. GDM also increases the risk for Diabetes Mellitus in future.  Early identification and management of GDM may reduce the risk for adverse events.

How do we identify GDM?

Healthcare professionals identify GDM using a screening and/or diagnostic test.

A screening test is used to identify pregnant women who are at increased risk (or decreased risk) for GDM based on a particular cutoff value for glucose. The woman is considered to have an increased risk for GDM if the glucose values are more than this cutoff value and a decreased risk for GDM if the glucose values are below this cutoff.

A screening test does not confirm a diagnosis; it only tells you if a person has a greater or reduced risk for the condition.

Once a positive screening test is obtained,  health care professionals do a diagnostic test to confirm the diagnosis.

When are the tests done?

The tests are usually done between 24 and 28 weeks of pregnancy.

What type of test criteria are used?

Different tests and criteria are used for the screening and diagnosis of GDM.  These include

  1.  National Diabetes Group and Carpenter & Coustan Criteria
  2. The American Diabetes Association (ADA) Criteria
  3. The World Health Organization (WHO) criteria
  4. The International Association of Diabetes and Pregnancy Study Group (IADPSG criteria)
  5.  National Institute for Health and Care Excellence (NICE) criteria
  6. Diabetes in Pregnancy Study Group India ( DIPSI) Criteria.

What do we know about the tests?

  1. Currently, the IADPSG criteria is more widely accepted for the identification of GDM
  2. The IADPSG criteria is currently endorsed by the ADA, the WHO, and several societies including the Endocrine Society, the Australian Diabetes in Pregnancy Society, the International Federation of Gynecology and Obstetrics (FIGO), several countries in Latin America and the European Board and College of Obstetrics and Gynecology.
  3. The IADPSG criteria uses a low cut off (>92md/dl) of blood glucose and hence misclassifies more women as having GDM
  4. This places a burden of care on health systems, which is a problem in low and middle income countries. Additionally, further research is needed on the management of mild GDM and the implications of treating a pregnant woman for mild GDM who does not really have GDM (the criteria does not misclassify on the moderate to severe spectrum of GDM).
  5. However, several studies have shown other benefits from using the IADPSG criteria for the identification of GDM.  These include decrease in other adverse pregnancy outcomes like preclampsia (a hypertensive disorder of pregnancy), Cesarean Sections,  larger than appropriate babies, low birth weight babies, and neonatal intensive care admissions.
  6. Doing a fasting plasma glucose in the first trimester is useful but may also misclassify women without GDM as having GDM
  7. The DIPSI criteria offers a more easier to perform strategy and is used widely in India and Sri Lanka.
  8. However, the results with DIPSI do not stack well when compared to the IADPSG or WHO criteria. The DIPSI criteria may tend to miss a substantial number of women who have GDM.

What should you know?

  1. Testing for the identification and management of GDM offers several benefits.
  2. The fact that there are several testing criteria to identify a single condition indicates an element of disagreement in what may be the most appropriate method to identify GDM.
  3. Each criteria uses different cutoff values and strategies (fasting, non fasting, one test, two test etc) for the identification of GDM.
  4. Because different criteria are used, the number of people identified with GDM will differ by the testing strategy and criteria used.
  5. Currently, the IADPSG criteria are more acceptable. These may change with further research.
  6. It is possible at the milder levels, with the IADPSG criteria,that you may be classified and treated for GDM when you do not have GDM. However,  this offers several indirect benefits to other problems associated with pregnancy.
  7. If you are diagnosed with GDM or been advised for a test to identify GDM, do discuss and confirm with your doctor if the IADPSG criteria is used.

 

Universal screening for GDM is now a policy in some states of India like Tamil Nadu.

If you are a pregnant woman who resides in any State or Union Territory of India, do discuss with your doctor or care giver about having a test for GDM between 24 and 28 weeks of pregnancy. Currently, the IADPSG criteria or a modified version of the IADPSG criteria will be a better test to identify GDM.


Click here for a scientific article by Bhavadharini et al. Clinical Diabetes and Endocrinology (2016) 2: 13 that reviews the screening and diagnosis of gestational diabetes mellitus with particular relevance to low and middle income countries.

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