Midwives should be given guidelines on how to advise expectant mothers about managing their weight, their professional body has said, reacting to research that suggested the commonly held belief that pregnant women needed to eat for two was a myth.

Gaining too much weight during pregnancy could put the future offspring at an increased risk of insulin resistance and affect their blood pressure in childhood, according to the study published in the journal Diabetologia.

The findings back up previous research that has suggested weight gain during pregnancy could have consequences, with a global study last year revealing 75% of pregnant women did not put on weight in a healthy fashion. Weight gain above or below recommended levels during pregnancy has been linked to various problems relating to the size of the baby and delivery.

“We need to educate the mother – it is not just [a] big [baby] they would have and now we have some evidence that it will affect the baby’s future,” said Prof Wing Hung Tam, the co-author of the study from the Chinese University of Hong Kong, although he said expectant mothers should not feel the need to start weighing themselves every other week.

Tam dismissed the idea of expectant mothers “eating for two”. The Royal College of Obstetricians and Gynaecologists note that women do not need extra energy for the first two trimesters and only need an extra 200 calories a day in the last three months of pregnancy.

“This research highlights the need for guidelines on weight gain in pregnancy in the UK,” said Mandy Forrester, the head of quality and standards at the Royal College of Midwives. She said that, in the absence of such advice, some British midwives have to “use their own initiative and refer to American guidance”.

Forrester added: “There is a clear need for midwives to have the tools, guidance and training they need so that they can offer women the best possible support and care. This is especially pressing because of the potentially serious complications that can arise in pregnancy as a result of women being overweight or obese. It is a real concern that some midwives do not have access to that most basic piece of equipment, scales.”

The mention of scales raised the spectre of a return to the weigh-in for expectant mothers. The NHS practice of routinely weighing women during pregnancy was phased out in the early 1990s on the grounds that it caused undue stress for little benefit.

In their article, Tam and colleagues described how they followed the health of 905 pairs of mothers and their children in Hong Kong.

The mothers’ weight before pregnancy was self-reported and the weight at delivery was taken from medical records, allowing both body mass index and weight gain during pregnancy to be calculated. The women were then classed as either gaining too much, too little, or recommended levels of weight – according to US guidelines – during pregnancy.

The results show that while 42% of women gained weight within the recommended levels during pregnancy, 17% gained too little and 41% gained too much – with women in the latter group more likely to be young, have a higher BMI, and a longer pregnancy.

Between 2009 and 2013, when the children were seven years old, the offspring were examined for measurements including weight, height, waist circumference and blood pressure.

After taking into account factors including the child’s gender, birthweight and age, maternal glucose levels during pregnancy, mode of delivery, and childhood exercise, the team found that children of women who put on more weight than guidelines recommended during pregnancy were more likely to be heavier, taller and have a higher BMI and waist circumference than offspring of women who gained the recommended levels of weight.

They also tended to have a higher blood pressure and signs of greater insulin resistance – factors the team found appeared, at least in part, to be linked to the children’s greater BMI.

The effects for children of mothers who gained less weight than recommended during pregnancy were less marked, possibly because there were fewer such children to study and less dramatic deviations from recommended weight gain, but there were some signs that such offspring might also have a slightly increased risk of insulin resistance and higher blood pressure.

Tam said the size of the effects were not necessarily cause for alarm and that the study only showed associations, while the children needed to be followed up into adulthood to further explore the effects. The team also noted that the pregnancy weight-gain guidelines were developed for American women, whereas the study involved only women of Chinese ancestry, and weight gain in pregnancy was not measured at multiple points in time.

Tam said women needed more support to monitor their weight throughout pregnancy and guidance on recommended levels of weight gain from the outset.

Debra Bick, a professor of midwifery and maternal health at King’s College, London, said the focus needed to be on helping women before they become pregnant.

“I would advise women planning pregnancy to think about their weight as it can have important life-long consequences for them and their child,” she said.

Dr Daghni Rajasingam, a spokesperson for the Royal College of Obstetricians and Gynaecologists, said: “These findings add to the growing body of evidence that shows the increase in risk of health complications from too much or too little weight gain during pregnancy.

“These findings have particular relevance in the UK where one in five pregnant women are obese. Women are encouraged to maintain a healthy weight before, during and after pregnancy by eating a well-balanced diet and taking part in regular exercise. It is also important to avoid dieting during pregnancy, even if a woman is obese, as this may harm the unborn baby.

“Having a healthy weight before conception increases the chances of falling pregnant naturally and reduces the risk of pregnancy and birth complications for both mother and baby.”