Women who are obese while pregnant have triple the risk of having a baby who develops type 2 diabetes later in life, research says.
The study of almost 120,000 women found pregnant woman who are overweight face a 40 per cent greater risk.
However, for expectant mothers who were obese while they were carrying their child, the risk was 3.5 times higher.
Scientists believe high blood sugar levels while the baby is in the womb may ‘programme’ them to develop the condition.
The researchers warn the findings are concerning, given one in two women of childbearing age in the UK tips the scales.
The data for the Edinburgh University study covered more than 60 years, in which time the level of obese mothers increased five-fold.
Lead researcher Professor Rebecca Reynolds said the study ‘showed a significant association’ between maternal BMI and children having diabetes.
Strategies to reduce obesity and overweight in women of childbearing age are urgently required, the team wrote in Diabetologia.
Professor Reynolds and colleagues analysed birth records of 118,201 children from 1950 to 2011.
These were compared to data from the national Scottish Care Information (SCI) – a diabetes register that covers every diagnosis in the entire population.
The reason for why a high BMI may lead to diabetes in unknown, and more studies are needed to explain the relationship, researchers said.
One theory is obesity in the mother produces an environment in the womb that is bad for the unborn baby’s health.
This includes high levels of glucose, insulin and other chemicals leading to a ‘programming’ of adverse metabolic outcomes for the child.
In addition, there are complex hormonal, metabolic and inflammatory changes linked to obesity in pregnancy.Professor Reynolds and her colleagues suggested these are likely to impact on hormonal exposure and nutrient supply to the foetus.
Metabolic changes that switch certain genes on or off – epigenetics – in the wombs of obese mothers may also play a part.
It could cause stress on the insulin producing beta cells in the pancreas of the unborn child, which can then lead to earlier onset of type 2 diabetes.
While the study took other factors that can affect the babies’ health into account, it did not include data on the BMI of the child or the lifestyle factors.
It is plausible, the authors suggest, that the link between high maternal BMI and offspring diabetes may be caused by increased BMI in the child.
Professor Reynolds said: ‘With the rising prevalence of being overweight or obese in women of childbearing age… our findings have profound public health implications.
‘There is an urgent need to establish effective approaches to prevention of obesity and diabetes among mothers and their offspring.
‘Pregnancy represents a potential time to intervene with health advice for the family.’
The data showed 25 per cent of the pregnant women were overweight and 10 per cent were obese across all years studied.
But the proportion of obese mothers has increased five-fold from the years 1950-1959 (three per cent) to the years 2000-2011 (16 per cent).
The short-term complications of maternal obesity are well recognised – including gestational diabetes that develops in the mother during pregnancy.
It also raises the risk of the dangerous complication pre-eclampsia, having larger infants and needing a C-section.
In a previous study, Professor Reynolds and colleagues found children born to obese and overweight mothers are more likely to die early of heart disease.
It showed a 35 per cent higher risk of dying before the age of 55 in adults whose mothers were obese in pregnancy.
The analysis included 28,540 Scottish women whose weight was recorded at their first antenatal check-up and their 37,709 now grown up children.