Diabetes which 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 is 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. 

Gestational diabetes is associated with an increased risk of complications, including pre-eclampsia (high blood pressure during pregnancy), excessive amniotic fluid, high birthweight babies, and emergency Caesarean sections. Children born to women with gestational diabetes are at greater risk of being obese and developing type 2 diabetes later in life.

The National Institute for Health and Care Excellence (NICE) brought in new guidelines in February, requiring two blood tests. A fasting blood sugar test reading of 5.6 mmol per litre or above is required for diagnosis of gestational diabetes. Although the threshold introduced by NICE has been lowered, Cambridge University research says it is still too high. The World Health Organization guidelines require three blood tests and a slightly lower reading of 5.1 mmol per litre.

Dr Claire Meek from the Welcome Trust-MRC Institute of Metabolic Science at the University of Cambridge, who is the author of the new study of diabetes in pregnancy, said there was a big difference between the WHO criteria and the NICE criteria. She commented: "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. While cost-effectiveness is important in any healthcare system, we must not forget the psychological and emotional distress that complications can cause."

The University of Cambridge study looked at 25,000 women giving birth at the Rosie Hospital in Cambridge between 2004 and 2008. It found that women with fasting blood sugar levels between 5.1 and 5.6 mmol per litre - 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 greater risk of having a baby with a high birth weight. 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 each year.

However, Professor Mark Baker, director of clinical practice at NICE, questioned the World Health Organization 2013 guidelines: "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. The WHO noted that its 2013 criteria may need rapid revision as economic data becomes available.” He welcomed the new research in this area.

Bridget Turner, director of policy at Diabetes UK, recommended that all pregnant women at risk of gestational diabetes should be screened and tested. She said: "It is extremely important that clinicians use their clinical judgement in identifying women who may need specific interventions to ensure safer and healthier pregnancies."