Posted on 14 September 2016
Published by The BMJ, the study finds a consistent association between higher blood glucose (sugar) levels during pregnancy and increased risk of complications around the time of birth, but there is no clear threshold of when to intervene with treatment.
Researchers say there is now an urgent need to work out the best threshold to balance the benefits and harms of treating women with high blood glucose levels during pregnancy.
Gestational diabetes - high blood glucose (sugar) levels during pregnancy - is associated with increased risk of a range of adverse outcomes around the time of birth and can affect the longer term health of mother and infant.
Although treatment can reduce the risk of these outcomes, the optimal glucose threshold to define gestational diabetes is unknown.
A team of researchers, based across the UK and Republic of Ireland, set out to examine the association between blood glucose levels in pregnant women without pre-existing diabetes and birth outcomes, such as whether they needed a caesarean section.
Looking at 23 studies involving over 200,000 women and their infants, mainly from high income countries across Asia, Australasia, Europe and North America, they explored the association between pregnancy blood glucose and outcomes for the mother and her baby.
When combining results there was a straight line association between glucose levels and caesarean section, induction of labour, a heavy baby, and shoulder dystocia (the baby getting stuck as their mother gives birth).
This means that, for each blood glucose increase, the risk of these problems increased by a similar amount - but there was no clear evidence of a threshold effect.
This straight line pattern was similar when the team looked at studies separately to explore the impact of study quality, type of glucose exposure and different geographical regions.These results showed that there is no obvious level to diagnose gestational diabetes.
Professor Trevor Sheldon, Dean of the Hull York Medical School and one of three University of York co-authors of the study, said: "These important results show the challenges of screening for conditions like diabetes and hypertension and deciding how to act on the results of tests.
“If the threshold is set low, too many women will be labelled as being at raised risk of having a baby who has problems at birth. On the other hand if the threshold is too high we will miss women who would have benefitted from treatment. Ultimately this comes down to balancing risks, costs and benefits. Health economists in the team are working on this and are due to report shortly.”