Obese women who develop gestational diabetes are five times more likely to have excessively large babies by six months of pregnancy, a new study found.
As well as affecting the mother’s health, the condition also causes the unborn child to grow larger, putting the mother at risk during childbirth.
It also increases the likelihood the baby will develop obesity and diabetes later on life.
Yet University of Cambridge scientist found excessive foetal growth began weeks before at risk women were screened for gestational diabetes.
Currently women are screened at eight to 12 weeks for gestational diabetes, but not offered a full blood glucose test until roughly 28 weeks into their pregnancy.
But by this time the unborn child has already grown excessively between 20 and 28 weeks.
Senior Research Associate Dr Ulla Sovio said: “Our study suggests that the babies of women subsequently diagnosed with gestational diabetes are already abnormally large by the time their mothers are tested for the disease.
“Given the risk of complications for both mother and child from gestational diabetes, our findings suggest that screening women earlier on in pregnancy may help improve the short and long term outcomes for these women.
“Early screening may be particularly beneficial for obese women as foetal growth is already abnormal by 20 weeks among these women.
“Any intervention aimed at reducing the risk of abnormal birthweight in the infants of obese women may need to be implemented even earlier.”
The study analysed data from 4,069 first time mothers, assessing the growth of their unborn babies using ultrasound scans.
Measuring the abdominal and head circumference of the foetuses, researchers compared the growth in mothers who developed diabetes.
They found that 4.2 per cent were diagnosed with diabetes beyond 28 weeks and saw no association between the size of the child at 20 weeks and the mother subsequently developing diabetes.
However scientists did find that the foetuses did grow excessively prior to diabetes diagnosis at between 20-28 weeks.
Professor Gordon Smith added: “We know that the offspring of women with gestational diabetes are at increased risk of childhood obesity, but so far no clinical trials have successfully demonstrated that screening and intervention in pregnancy reduces this risk.
“Our study suggests a possible explanation: screening and intervention is taking place when the effects of gestational diabetes are already manifested in the foetus.
“The evidence from our study indicates that there is an urgent need for trials to assess the effect of earlier screening, both on the outcome of the pregnancy and the long term health for the offspring.”
The stillbirth charity Sands welcomed the research and acknowledged that gestational diabetes plays a large part in avoidable stillbirths.
Janet Scott said: “We know from recent enquiries that failure to screen for gestational diabetes currently plays a part in a significant number of potentially avoidable stillbirths at term.
“Good risk assessment is crucial to avoiding harm to mothers and babies and we welcome these important findings which have real potential to inform better antenatal care for these high risk pregnancies.
“We are delighted to have supported this research, funded with donations from bereaved families.”
The study was published in the journal Diabetes Care.