A recent article in The Conversation has stirred the pot by questioning the value of diagnosing and treating gestational diabetes in pregnant women. Bond University Professor of Medicine Paul Glasziou and University of Queensland Clinical Professorial Research Fellow Jenny Doust cited one in six pregnant women now diagnosed with the condition – a doubling of cases since new criteria was developed in 2010. They argued the glucose test used was unreliable, some women were tested too early, and the thresholds were too low. Their article referred to findings from a recent randomised controlled trial – the Treatment of Booking Gestational Diabetes Mellitus (TOBOGM) study published in The New England of Journal of Medicine – suggesting it showed no benefit from testing and treating women with risk factors early in pregnancy.
Medical Forum asked one of the authors of the TOBOGM paper, Perth endocrinologist Dr Emily Gianatti, to respond. She expressed concern that women and their health care providers, after reading this article may choose not to have or offer testing or treatment for gestational diabetes, despite there being clear evidence that it benefits women and their babies, and made these points:
Significant evidence exists that shows treatment of gestational diabetes benefits women and their babies particularly in reducing risk of fetal overgrowth, serious perinatal outcomes including shoulder dystocia, and hypertensive disorders of pregnancy. A diagnosis of gestational diabetes also identifies women and babies who are at greater risk, beyond pregnancy, of diabetes and overweight, allowing for targeted support and intervention.
There has been a significant increase in recent decades in the incidence of gestational diabetes in Australia, in part related to changes in diagnostic practices as acknowledged by the authors of the article, but also due to increasing risk factors for gestational diabetes in our society.
Overweight and obesity are known risk factors for gestational diabetes, with rates in Australian women increasing from 49.4% in 1995 to 59.7% in 2018. Ethnicity is also a known risk factor with the incidence of gestational diabetes being higher among Asian, Indian subcontinent, Aboriginal, Torres Strait Islander, Pacific Islander, Maori, Middle Eastern and non-white African women. In recent decades there has been significant change in Australia in where migrant women were born, with a majority now from Asian countries. The average maternal age at birth also continues to rise with the incidence of gestational diabetes rising also with mother’s age.
The authors highlighted results of the recently published GEMS study. In this study pregnant women were randomly assigned at 24-32 weeks pregnancy to be evaluated for gestational diabetes by a 75g two-hour oral glucose tolerance test using lower (WHO 2013 criteria) or higher (current NZ criteria) glycaemic criteria for diagnosis.
As the authors assert there was no difference between the groups in relation to incidence of large-for-gestational-age infants. Importantly, neonatal hypoglycaemia was detected and treated more frequently among the infants in the lower glycaemic criteria group. This is most likely due an increased percentage of infants born to a mother with a diagnosis of gestational diabetes who therefore are identified as requiring screening for hypoglycaemia according to hospital protocols.
Some infants born to mothers in the higher glycaemic criteria group may have had undetected hypoglycaemia that was not treated. Neonatal hypoglycaemia is associated with later adverse neurodevelopment. In addition, in a pre-specified subgroup analysis, women whose glucose levels fell between the two groups (fasting glucose 5.1- <5.5 mmol/L, 1-hour glucose >=10 mmol/L or 2-hour glucose 8.5 – <9.0 mmol/L) were compared according to whether they were treated. Those who were treated had better outcomes overall with fewer babies that were LGAs while the number needed to treat to prevent one LGA baby was four.
The authors highlighted the results of the TOBOGM study, an international, multi-site, randomised controlled trial assessing the impact of diagnosing and treating gestational diabetes early in pregnancy (<20 weeks) in women who had risk factors for diabetes. Contrary to the authors’ comments, this study showed early treatment of gestational diabetes before 20 weeks’ gestation led to lower incidence of the primary outcome of composite of adverse neonatal outcomes (birth <37 weeks, birth trauma, birth weight >4500g, respiratory distress (distress warranting >=4 hours of supplemental oxygen, continuous positive airway pressure or intermittent positive pressure ventilation in the first day of life), phototherapy, stillbirth or neonatal death or shoulder dystocia).
Over one in 20 babies avoided a group of severe birth complications, respiratory distress was almost halved, the number of days needed in neonatal intensive care or special care unit were down by 40% and severe perineal injury was reduced by three quarters. More study is required to determine how these findings should be translated to clinical care.
The authors raise an important point that a diagnosis of gestational diabetes does impact women’s experience of pregnancy, and health care professionals providing care to these women need to provide empathic, woman-centred care.
Most women will not require pharmacotherapy and in these cases less frequent monitoring of blood glucose levels is appropriate. Ongoing food diaries are not required in most patients and it is not usual practice for babies to be separated from mother for monitoring of blood glucose levels as compared to treatment of severe hypoglycaemia not responding to first line treatments.
It is expected that over time clinical guidelines will change in response to new findings. However women and their treating health care professionals can remain confident that diagnosing and treating gestational diabetes remains important in reducing risk for women and their babies.
ED: Dr Emily Gianatti is an endocrinologist at St John of God Murdoch. References to the research cited is available from Medical Forum on request.