Pregnancy diabetes guidelines 'could miss 4,000 women'
New criteria for diagnosing diabetes during pregnancy could be missing thousands of at-risk women, a report suggests.
Although the threshold introduced by health watchdog NICE earlier this year has been lowered, Cambridge University research says it is still too high.
The WHO's threshold is lower and identifies more women at risk of pregnancy complications.
Diabetes UK said it was vital that women received the right support.
Diabetes that occurs for the first time during pregnancy is known as gestational diabetes.
It is estimated to affect around 4%-5% of pregnant women in the UK and has becoming increasingly common in line with the rise in obesity.
In some women, the condition occurs because the body cannot produce enough insulin to meet the extra needs of pregnancy.
In others, diabetes may be found during the first trimester of pregnancy or may have existed before the pregnancy.
If left untreated, the condition can be a risk to the health of the mother and baby, potentially leading to birth defects, babies being born overweight and emergency C-sections. Miscarriage is also a danger.
The National Institute for Health and Care Excellence (NICE) brought in new guidelines in February, requiring two blood tests (one when fasting and another two hours after a sugary drink). A fasting blood sugar test reading of 5.6 mmol per litre or above is required for a diagnosis of gestational diabetes.
The World Health Organization guidelines require three blood tests and a slightly lower reading of 5.1 mmol per litre for the fasting blood sugar test.
Study author Dr Claire Meek from the Wellcome Trust-MRC Institute of Metabolic Science at the University of Cambridge, said there was a big difference between the WHO criteria and the NICE criteria.
"The international criteria are based on minimising the risk of harm to the mother and baby, whereas the NICE criteria have been based upon reducing costs to the NHS."
She added: "While cost-effectiveness is important in any healthcare system, we must not forget the psychological and emotional distress that complications can cause."
It found that women with fasting blood sugar levels between 5.1 and 5.6 mmol per litre - those who would be missed under the new NICE criteria - were twice as likely to have an emergency Caesarean section and seven times as likely to have excessive amniotic fluid. They were also at higher risk of having a baby with a high birth weight.
Dr Meek said there was "not a great amount of evidence" to guide experts but she felt it was important to make sure "we direct resources to people who would really benefit".
The report said the higher readings required in the UK, compared with other countries, could mean that as many as 4,000 women with diabetes in pregnancy were not being cared for.
'Not enough benefit'
But Prof Mark Baker, director of clinical practice at NICE, said the jury was still out on the World Health Organization 2013 criteria.
"The expert NICE guideline development group undertook careful analysis with an economic model that showed the WHO 2013 criteria were not cost-effective; their criteria did not provide enough benefit in relation to the increased costs.
"In addition, the WHO recommendation was weak and the WHO noted that their 2013 criteria may need rapid revision as economic data becomes available.
He added: "We welcome new research in this important area and will keep the guideline under surveillance."
Bridget Turner, director of policy at Diabetes UK, said all pregnant women at risk of gestational diabetes should be screened and tested.
"It is extremely important that clinicians use their clinical judgement in identifying all pregnant women who may need specific interventions to ensure safer and healthier pregnancies.
"For women diagnosed with gestational diabetes, it is vital that that they receive the right information about their diagnosis as well as the support and care they need."
Women with gestational diabetes are normally given dietary and lifestyle advice or treated with tablets or insulin.