Predictors of Gestational Diabetes Persistence Require Follow-Up

Kate Johnson

December 05, 2011

December 5, 2011 (Dubai, United Arab Emirates) — Ethnicity and insulin use during pregnancy offer clues as to which women with gestational diabetes mellitus (GDM) are more likely to convert to type 2 diabetes mellitus, according to research presented here at the International Diabetes Federation World Diabetes Congress 2011.

Compliance with postpartum screening is notoriously poor, and until this is improved, such predictions are of questionable value, warn Kim John Ly, a medical student at the University of Leicester Hospitals NHS Trust in the United Kingdom, and colleagues.

Using criteria for the diagnosis of GDM that have been proposed by the International Association of Diabetes and Pregnancy Study Groups (IADPSG), an expected spike in the diagnosis of GDM might lead to a similar spike in the number of patients at risk for conversion to type 2 diabetes, said Boyd Metzger, MD, from Northwestern University Feinberg School of Medicine in Chicago, Illinois. Dr. Metzger was chair of the session and a member of the IADPSG guidelines writing group.

"The biggest thing about postpartum testing is the poor rate of compliance," he said in an interview with Medscape Medical News. "That's an almost universal finding, [and is] a really huge barrier to overcome. If we expand the population [using the proposed criteria], the risk [of conversion] for the people who have the mildest glucose intolerance is more delayed. We need a new strategy for testing postpartum because we will lose even more."

The retrospective study looked at 396 patients diagnosed with GDM on the basis of 1 oral glucose tolerance test at 24 to 28 weeks of gestation.

The diagnosis was made with a fasting plasma glucose level of 5.5 mmol/L or higher and/or a 2-hour plasma glucose level of 7.8 mmol/L.

Mean age of the patients was 32 years, and mean body mass index was 29.5 kg/m². Half of the cohort was white, 27.5% was South Asian, 10.9% was Afro-Caribbean, and the rest was categorized as "other."

Postpartum screening scheduled at 6 weeks postpartum was attended by only 189 patients (47.7%), the majority of whom had returned to normal glucose tolerance (78%). However, 22% had some degree of glucose intolerance or frank diabetes, he said.

Specifically, 3.2% had isolated impaired fasting glucose, 11% had isolated impaired glucose tolerance, 2.1% had both, and 5.8% had developed type 2 diabetes.

Conversion rates for white subjects were slightly lower (9.1%) than for South Asians (11%), Afro-Caribbeans (13%), and subjects of other ethnic origins (13%), but the difference was not significant, reported Mr. Ly.

When use of insulin during pregnancy was considered, a significantly higher proportion of converters required this treatment than nonconverters (62% vs 34%; P = .005), he explained.

Any trend in differences between ethnicities can be explained by the difference in the use of insulin during pregnancy, said Dr. Metzger, who has performed similar analyses.

"The closer you are to diabetes in pregnancy, the sooner you will become diabetic. If you adjust for how severe the GDM is at the time of diagnosis, there really aren't ethnic differences."

He said the poor antenatal compliance with screening in the study is more of an issue.

"It's a big concern. It identifies a group at very high risk for diabetes and is a great opportunity for prevention efforts, yet we aren't able to engage people as much as we'd like."

The study authors and Dr. Metzger have disclosed no relevant financial relationships.

International Diabetes Federation (IDF) World Diabetes Congress 2011: Abstract O-0395. Presented December 5, 2011.