Women who are hoping to conceive should go on a diet years before, new research suggests.
Writing in The Lancet, medics said the vast majority of women of reproductive age were not nutritionally prepared for pregnancy – putting the long-term health of their children at risk.
Those thinking about starting a family are often advised to make lifestyle changes, such as cutting out alcohol, and taking dietary supplements, around three months before attempting to conceive.
But the experts said one of the most crucial factors was for women to be a healthy weight before conception – often meaning diet and lifestyle overhauls need to start years earlier.
And they said school children should be taught about the importance of the right diet to prepare for parenthood.
Researchers calculated the proportion of women of reproductive age in Britain who are nutritionally prepared for pregnancy, using data from 509 women of reproductive age in the UK National Diet and Nutrition Survey.
In total, 96 per cent were found to have iron and folate dietary intakes below the recommendation for pregnancy. Such shortfalls can be tackled in less than a month.
But lead authors from University College London said more longer-term efforts were needed to tackle soaring levels of obesity among parents-to-be.
Research suggests more than one quarter of pregnant women are overweight or obese.
Excess weight in pregnancy increases the lifelong risk of cardiovascular, metabolic, immune and neurological diseases in subsequent children.
Links have also been made between male obesity and poor sperm quality, which may also increase the risk to future children, though the evidence is less clear.
Lead author Professor Judith Stephenson, of University College London, said: “The preconception period is a critical time when parental health – including weight, metabolism, and diet – can influence the risk of future chronic disease in children, and we must now re-examine public health policy to help reduce this risk.
“While the current focus on risk factors, such as smoking and excess alcohol intake, is important, we also need new drives to prepare nutritionally for pregnancy for both parents.”
Professor Janice Rymer, Vice President of the Royal College of Obstetricians and Gynaecologists (RCOG), said she was “extremely concerned” by the findings.
“This highly significant research presents stark evidence of the importance of nutrition and lifestyle in the preconception period,” she said.