The season may affect gestational diabetes mellitus (GDM) prevalence, possibly leading to misdiagnosis, according to Greek researchers.
In a retrospective and a prospective analysis, higher temperatures in Greece were associated with a higher prevalence of GDM diagnoses, reported Eleni Anastasiou, MD, of the Alexandra Hospital in Athens, and colleagues.
They found prevalence of GDM cases, diagnosed during the third trimester of gestation, were lowest during the winter (P<0.0001):
- Winter: 28.1% GDM prevalence
- Spring: 32.4%
- Summer: 39.2%
- Autumn: 32.4%
Compared with the winter, women had significantly higher odds of being diagnosed with GDM when tested in the summer (OR 1.65, 95% CI 1.43-1.90), as well as the spring or autumn (OR 1.23, 95% CI 1.08-1.39), they wrote in the European Journal of Endocrinology.
“Our findings suggest the need to take into consideration environmental temperature during interpretation of test results used to diagnosed GDM,” said Anastasiou in a statement. “We hypothesize that the seasonal changes observed may be due to an increase in blood flow that may diminish sugar extraction from blood to tissue.”
“Better screening should ensure that pregnant women are properly diagnosed for GDM, ensuring they receive treatment only when their blood sugar levels can pose a danger for themselves and the baby, and avoiding unnecessary treatment and distress during pregnancy,” Anastasiou added.
Although other researchers have previously explored this potential link, the findings were generally mixed, the authors noted.
The retrospective analysis included 7,618 pregnant women from Greece. All the women had a 3-hour 100g oral glucose tolerance test during the third trimester.
Rising monthly temperatures were associated with increased odds of GDM, with the highest odds reported in June (OR 1.60, 95% CI 1.26-2.04), July (OR 1.88, 1.49-2.38), and August (OR 1.84, 1.42-2.37), where the mean monthly temperatures were 77°F (25°C), 82.4°F (28°C), and 82.4°F (28°C), respectively.
In the prospective analysis, which included 768 pregnant women in their third trimester of pregnancy, a 75 g oral glucose tolerance test was administered in a climate-controlled room. During this 18-month analysis, the outdoor temperature was also noted daily at 9 a.m.
Although no differences were seen at the start of the glucose tolerance test between groups, there were notable differences in glucose readings, stratified by temperature exposure, 60 minutes and 120 minutes into the test:
- <76.8°F: 143 mg/dL (60 min); 117 mg/dL (120 min)
- 77°F to 85.8°F: 148 mg/dL (60 min); 117 mg/dL (120 min)
- >86°F: 155 mg/dL (60 min); 125 mg/dL (120 min)
Similar findings were reported for the percentage of those with abnormal glucose levels at 60 minutes and 120 minutes, stratified by temperature exposure range.
“These findings are in accordance with the results of previous experimental studies which showed that post-load blood glucose levels were higher at higher ambient temperatures,” the group wrote, adding that “higher post-prandial glucose levels observed when patients are exposed at higher ambient temperatures could be attributed to alterations of the blood flow pattern.”
“Exposure to high temperature induces the possible opening of arterio-venous thermoregulatory anastomoses. This could lead in turn to increased blood flow and venous blood arterialization and therefore decreased glucose tissue extraction,” they noted.
Study limitations include the location of both analyses, which occurred at Alexandra Hospital. This is a referral center for high-risk pregnant women, which may have led to a disproportionately large amount of GDM cases.
Although the potential for these “temperature induced differences” in glucose levels are unlikely to affect the diagnosis of individuals with “unequivocal diabetes,” the researchers argued temperature exposure should be taken into consideration when healthcare providers interpret oral glucose tolerance tests for diagnosing gestational diabetes mellitus.
Anastasiou and co-authors disclosed no relevant relationships with industry.
Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner