The research, published in the British Medical Journal, looked at data from 12,500 women across 16 countries. It found that women of any weight who consumed a healthy diet and did regular exercise in pregnancy reduced excessive weight gain, gestational diabetes and the risk of requiring a caesarean section.
The participants in the study were advised to restrict sugary drinks, switch to low-fat dairy and eat more fruit and vegetables.
The women also took part in a structured exercise programme that included aerobic classes, stationary cycling and resistance training.
Researchers found no strong evidence to suggest that exercise and a healthy diet had a negative effect on the baby, such as being small or large for gestational age or needing admission to a neonatal intensive care unit.
Researchers hope that this will reassure mothers who have traditionally been advised not to exercise in pregnancy.
One of the authors, Professor Shakila Thangaratinam, said,
"Our findings are important because it is often thought that pregnant women shouldn’t exercise because it may harm the baby.
‘But we show that the babies are not affected by physical activity or dieting, and that there are additional benefits including a reduction in maternal weight gain, diabetes in pregnancy, and the risk of requiring a caesarean section.
‘This should be part of routine advice in pregnancy, given by practitioners as well as midwives."
Professor Thangaratinam added that for every 40 women who consume a healthy diet and exercise programme in pregnancy, there will be one fewer having a caesarean section.