Pregnant women have been told they don't need to eat for two to have a healthy baby.
And women worried about their weight have been reassured that dieting doesn't risk their unborn baby's health.
The British Medical Journal analysis said not eating for two but following a healthy diet prevents excess weight gain.
The researchers looked at the findings from 44 previous studies involving more than 7,000 women.
Previous advice has suggested dieting during pregnancy "may harm the health of the unborn child".
But the new review, funded by the National Institute of Health Research (NIHR), compared diet, exercise or a combination of the two and found that women who followed a calorie-controlled diet had significantly fewer complications.
Dr Shakila Thangaratinam, a consultant obstetrician at Queen Mary, University of London who led the study, told the BBC: "We are seeing more and more women who gain excess weight when they are pregnant and we know these women and their babies are at increased risk of complications.
"Weight control is difficult but this study shows that by carefully advising women on weight management methods, especially diet, we can reduce weight gain during pregnancy.
"It also shows that following a controlled diet has the potential to reduce the risk of a number of pregnancy complications."
She added: "Women may be concerned that dieting during pregnancy could have a negative impact on their babies. This research is reassuring because it showed that dieting is safe and that the baby's weight isn't affected."
However, Dr Janine Stockdale, research fellow at the Royal College of Midwives, said:
We should be careful to note that the researchers are not advising women to lose weight during pregnancy; this is about managing excessive weight or weight gain.
"If a woman is on target to gain the right amount of weight during her pregnancy, then 'dieting' and 'calorie-controlled dieting' as we commonly understand these terms, is not for her.
"We need to reassure women that under the care of a midwife or other health professional, weight management is safe."