They also raised questions about current screening rates among those at risk of gestational diabetes.
“There’s good news and there’s bad news”
The study found that the risk of stillbirth was over four-times higher in women who developed signs of gestational diabetes but were not diagnosed.
However, with appropriate screening and diagnosis that increased risk of stillbirth disappeared, noted the study authors from the University of Leeds and the University of Manchester.
The study, published in BJOG: An International Journal of Obstetrics and Gynaecology, was funded by charities including Action Medical Research, Cure Kids, Sands and Tommy’s.
The research project came out of a Stillbirth Summit in 2011 and was created with the help of more than 550 parents and members of the public.
Those behind the project highlighted that it was designed by and for parents, to try to maximise the positive impact it could have on society.
The study compared the symptoms and care of 291 women who experienced a stillbirth to 733 similar women who did not experience a stillbirth across 41 maternity units in England.
Researchers found that across all women with high blood glucose, measured after a period of fasting, they had on average twice the risk of stillbirth than women without the condition.
“Maternity units should follow NICE clinical guidance to ensure women are diagnosed and supported”
The increased risk was likely to be caused by the missed diagnoses and lack of subsequent care experienced by many of the women, noted the researchers.
However, they cautioned that the results showed an association only and cannot provide certainty about cause and effect.
Dr Tomasina Stacey, who led the study at the University of Leeds and now works at the University of Huddersfield, said: “There’s good news and there’s bad news.
“The good news is that women with gestational diabetes have no increase in stillbirth risk if national guidelines are followed for screening, diagnosis and management,” she said.
“The bad news is that the guidelines are not always followed and some women, therefore, experience avoidably higher risk,” said Dr Stacey.
According to recent figures, approximately 5% of women in the UK experience gestational diabetes during pregnancy.
The National Institute for Health and Care Excellence’s guidance recommends that all women at a higher risk of gestational diabetes should receive blood screening for the condition.
The NICE screening criteria includes women with a raised body mass index of over 30, or those from South Asian or Black Caribbean ethnic groups.
But the researchers found only 74.3% received screening among the women participating in the study with a raised BMI and 74.7% of those from South Asian or Black Caribbean ethnic groups.
“It’s important that we detect every woman with symptoms so she can receive the appropriate care and support”
On average, women at higher risk of gestational diabetes who were not screened in line with the NICE guidelines also experienced higher risks of stillbirth.
Study co-author Professor Alexander Heazell, from the University of Manchester and clinical director of Tommy’s Stillbirth Research Centre, said: “It’s not clear why some women missed out on being screened or diagnosed for gestational diabetes, but this needs to be improved.
“Gestational diabetes can cause serious complications in pregnancy,” he said. “It’s important that we detect every woman with symptoms so she can receive the appropriate care and support.”
In 2015, the NICE raised the threshold for diagnosing gestational diabetes to a fasting plasma glucose concentration of greater than 5.6mmol/L.
In the US the threshold is 5.1mmol/L, and there is considerable debate worldwide about the appropriate level for diagnosis.
The present study found little evidence to support one threshold over another, instead finding that the risk of stillbirth increased steadily with increasing glucose concentration.
Dr Stacey, who also works at Calderdale and Huddersfield NHS Foundation Trust, said: “There’s no blood sugar level where the risk suddenly jumps.
“The choice of the right threshold for diagnosis is therefore more about pragmatism and finding the right balance of risk to resource, and avoiding over-medicalisation,” she said.
She added: “Our study shows that the current NICE guidelines can be effective, but only if they are followed.”
According to recent figures from MBBRACE-UK, around four in every thousand pregnancies in the UK result in stillbirth.
Mr Edward Morris, vice president of clinical quality at the Royal College of Obstetricians and Gynaecologists, said: “Women with gestational diabetes are more likely to have a stillbirth, but with adequate monitoring, care and treatment, this risk can be managed so that women can maximise their chances of having a healthy pregnancy and birth.
“Maternity units should follow NICE clinical guidance to ensure women are diagnosed and supported to avoid complications and ensure the best possible outcomes,” he said.
Meanwhile, the study is unique in that it separated the harmful biological effects of raised glucose from the benefits of diagnosis, which typically leads to better care and management of the condition.
Study co-author Dr Peter Tennant, from the University of Leeds and the Alan Turing Institute, highlighted that it was important because there was “a lot of debate about the true impact of gestational diabetes”.
But he added: “Only when you look at women who aren’t appropriately screened or diagnosed, does the full impact of gestational diabetes become clear.”