Women are being urged to maintain a healthy weight before and during pregnancy to prevent a "time bomb" of children developing diabetes.
Research has shown that babies born to mothers who have gestational diabetes in pregnancy are six times more likely to develop Type 2 diabetes in later life.
The charity Diabetes UK said women should keep to a healthy weight while trying to conceive and not gain too much weight in pregnancy to lower the risk of gestational diabetes.
According to the NHS, up to 18% of pregnant women develop gestational diabetes, which is caused by too much glucose in the blood.
The condition usually disappears after the baby is born but there are long-term health risks for mother and child.
Type 2 diabetes can lead to early death, heart disease, kidney failure and the need for amputation.
Gestational diabetes is also linked to premature birth, the need for a Caesarean section and high blood pressure in pregnancy.
New guidelines from the National Institute for Health and Care Excellence (Nice) lower the threshold for diagnosing gestational diabetes, meaning more women are expected to be diagnosed in the future.
Diabetes UK said increasing rates of gestational diabetes could mean a "health time bomb" for children going on to develop Type 2.
Mothers also have seven times the risk of developing Type 2 if they have experienced gestational diabetes.
Barbara Young, chief Executive of Diabetes UK, said: "It is well established that gestational diabetes is a serious health issue that can cause birth defects, stillbirth and complications for the mother.
"But it is also important that women understand that gestational diabetes leaves a frightening legacy, putting the child at increased risk of a serious health condition which, if poorly managed, can lead to complications such as kidney disease, stroke and amputation.
"Given that we know being overweight significantly increases risk of gestational diabetes, we need to get across the message to women that making sure they are a healthy weight is important for their child's health and that this health benefit may stretch many years into the future."
Douglas Twenefour, clinical advisor at Diabetes UK and author of the charity's new guide on the issue, said: "By giving mums-to-be all the information they need to help them manage their condition, we aim to reassure them and help them to achieve safer and happier pregnancies, reducing the short-term and long-term risks to mother and child."
Research published in June in BJOG: An International Journal of Obstetrics & Gynaecology found that women who exercised during pregnancy are less likely to have gestational diabetes.
Other risk factors include having the condition during a previous pregnancy, having a previous child who weighed more than 10lbs at birth and being over the age of 25.
Women from a South Asian, black, African Caribbean or Middle Eastern background also have a higher risk.
According to the NHS Choices website, up to 18% of women suffer gestational diabetes in pregnancy.
Nice puts the figure at 5%.
Dr David Richmond, president of the Royal College of Obstetricians and Gynaecologists (RCOG), said: "Gestational diabetes is very common, affecting around one in five women during pregnancy.
"Most women who develop diabetes in pregnancy have healthy pregnancies and healthy babies but occasionally gestational diabetes can cause serious problems, especially if it goes unrecognised.
"Immediate changes to lifestyle, including a healthy diet and moderate levels of exercise can have significantly positive effects on a woman and her baby's health."