Gestational diabetes mellitus (GDM) is one of the most common complications of pregnancy. Almost six percent of pregnant women are affected. In these women, the altered hormone balance also affects the metabolism, and blood glucose levels are elevated. Most women with GDM have normal blood glucose levels again after giving birth. However, their risk of developing type 2 diabetes mellitus later in life increases. In order to avoid possible complications during pregnancy or at birth, as well as secondary diseases in mother and child, it is important to diagnose and treat gestational diabetes at an early stage. That is why pregnant women are screened for GDM between the 24th and 28th week of pregnancy and, if necessary, receive a diagnostic oral glucose tolerance test **(OGTT). To simplify this procedure during the pandemic, a British study by the authors Meek et al. suggests an HbA1c threshold of 39 mmol/mol (5.72 %) for the 28th week of pregnancy to detect GDM . Researchers of the DZD have now investigated in the PREG study whether the procedure can also be adopted for health care in Germany.
Therefore, in addition to two oral glucose tolerance tests (24 + 0 and 31 + 6 weeks of pregnancy), HbA1c was also determined. The researchers diagnosed 118 GDM cases out of 440 pregnancies. Using the HbA1c value of 5.72% proposed by Meek et al., GDM was detected in 12 women. GDM could not be diagnosed in 106 women using this criterion. Eight of the women with normal glucose metabolism had an HbA1c value above this cutoff. The specificity of the proposed HbA1c threshold was 97.5%, but the sensitivity was only 10.2%.
"Our analysis shows that in the second and third trimester, respectively, an HbA1c value of 5.72 % is not suitable for diagnosing GDM. Most patients with GDM (89.8%) would have been missed and not treated using this method," said Professor Martin Heni, summarizing the study results. "The use of the HbA1c threshold mainly identifies pregnant women with elevated fasting blood glucose, while women with normal fasting blood glucose but high post-meal glucose spikes are overlooked."
Fritsche L, Peter A, Hummel J, Wagner R, Häring HU, Birkenfeld AL, Fritsche A, Heni M: HbA1c measurement cannot replace an oral glucose tolerance test for the diagnosis of gestational diabetes. Dtsch Arztebl Int 2021; 118: –. DOI: 10.3238/arztebl. m2021.0159
* German Gestational Diabetes Study – PREG
Within the German Gestational Diabetes Study, pregnant women with and without gestational diabetes are given follow-up examinations over a period of ten years in order to detect pre-diabetes stages and, if necessary, to offer preventive measures. The study is being conducted at five locations throughout Germany within the framework of the German Center for Diabetes Research (DZD).
** Oral glucose tolerance test (OGTT)
The oral glucose tolerance test (OGTT) can be used to determine how well the body can process a large amount of glucose. In the test, the patient drinks a precisely defined amount of glucose dissolved in water. After one hour, blood is taken from the arm vein and the blood glucose value is determined.
1) Meek CL, Lindsay RS, Scott EM, et al.: Approaches to screening for hyperglycaemia in pregnant women during and after the COVID-19 pandemic. Diabetic Medicine n/a:e14380.