'Casual' gestational diabetes test misses 70% of cases

When screening pregnant women for gestational diabetes, casual blood glucose testing misses 70% of cases. That’s according to a study conducted by Kobe University and published in the Journal of Diabetes Investigation, which should encourage obstetricians to depend on more reliable tests to help prevent pregnancy complications.

Gestational diabetes mellitus is a condition where previously healthy women exhibit high blood sugar levels during pregnancy. If treated, most women deliver healthy babies, but if left unmanaged, this can lead to pregnancy complications, babies growing larger than usual, and an increased risk of developing type 2 diabetes later for both the mother and the child.

The International Association of the Diabetes and Pregnancy Study Groups recommends that all women who have not been diagnosed with diabetes previously undergo an oral glucose tolerance test between weeks 24 and 28. This requires women to fast for 8–12 hours before a baseline blood sample is taken, then drink a solution containing a standardised amount of glucose, with another blood sample taken later to see how well the body metabolises the sugar.

However, many health facilities use a much simpler, cheaper and quicker ‘casual’ blood glucose test for which blood is taken and analysed for glucose levels only once, without consideration to what or when women have eaten before; only if women test positive in that screening are they asked to undergo the more rigorous glucose tolerance test. This caused Kobe University obstetrician Kenji Tanimura and graduate student Masako Tomimoto to wonder if this approach misses cases with diabetes.

Working in the perinatal centre of Kobe University Hospital, the researchers combined the casual blood glucose screening and another standard test for gestational diabetes, the much more sensitive glucose challenge test, into a single protocol for all visiting women; those who tested positive in the glucose challenge test were also asked to take the glucose tolerance test. Out of the 99 women who in the end were diagnosed with gestational diabetes mellitus, 71.7% had blood sugar levels in their original blood sample that would have resulted in a negative diagnosis.

“Although there have been studies showing that the casual blood glucose test is less sensitive than others, no studies have directly compared the results in the same individuals,” Tomimoto said. “Our study confirmed that this screening method, which is widely used in practice, frequently misses the condition it is meant to detect.”

To see how widespread this issue is, the team also conducted a survey among healthcare facilities in Hyōgo Prefecture, where Kobe University is based. They found that 43% of the respondents who used blood glucose tests relied only on the casual screening.

“In Japan, where about half of all deliveries take place in obstetric clinics rather than in hospitals, the more accurate but complicated and time-consuming tests are not widely used,” Tomimoto said. Similar surveys have shown that in the UK, 48% of clinics also rely on only the casual blood glucose test for the first screening.

Tanimura concluded, “We hope that our data can contribute to improvements in the management system and to the revision of the guidelines for gestational diabetes mellitus screenings. The goal is to protect more mothers and babies from gestational and childbirth issues caused by this form of diabetes, and in general reduce the risk of developing the disease in the future.”

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