Children born to mothers with high blood sugar levels during pregnancy are 50 percent more likely to become overweight or obese during early adulthood, according to a comprehensive study that spanned two decades.

The findings were made by the Chinese University of Hong Kong's faculty of medicine after researchers tracked over 500 mother-child pairs since early 2000s. The mothers were invited for follow-up consultations seven, 11 and 18 years after the study began.

The team also found that pregnant women who are overweight and suffer from gestational diabetes, which affects one in six pregnancies in Hong Kong and globally, produce offspring that are seven times more likely to have increased body fat accumulation during childhood.

"We found a strong relationship between levels of glucose during pregnancy in the mother, and the glucose levels in the children, 18 years after delivery," said Professor Ronald Ma, who studies endocrinology and diabetes.

"[That] means the mother's glucose level during pregnancy is kind of like a predictor of what would happen to the child in terms of risks of abnormal glucose or diabetes, as well as being overweight.

"It highlights that gestational diabetes is an important condition which we need to pay attention, to identify these abnormal glucose levels and treating it."

Apart from children, Ma noted that pregnant women who suffer from gestational diabetes are also at higher risk of developing diabetes later in life.

But the expert said the disease is manageable by diet modifications, while insulin injections and oral medication may be prescribed in some cases.

"I think the important thing is to have it identified, and then have professional advice and guidance as to how best to control the glucose, because this is very much individualised depending on the glucose levels during pregnancy, as well as the stage of pregnancy," he said.

Ma said these mothers should continue to take blood glucose level readings six to 12 weeks after delivery, to allow for early detection of diabetes.

Still, the most effective means of avoiding gestational diabetes is to adopt a healthy lifestyle early, the professor said, instead of trying to lose weight after planning for pregnancy.

He also recommended light jogging and exercise for mothers-to-be, as opposed to the common belief that they should avoid physical exertion.