A review of 36 studies in 16 countries found that a careful diet and exercising helped reduce excessive weight gain in pregnancy and enabled more women to deliver naturally.
Around one in four births in the UK are by Caesarean which, although regarded as very safe, can carry a risk of complications.
These include the risk of infections to new mothers, excessive bleeding and potential damage to surrounding organs.
Risks to the baby include breathing problems, which are fairly common and mostly affect babies born before 39 weeks gestation.
This usually improves within a few days.
Of the studies in the new analysis, 23 included women of any weight at the start of the study, seven included obese women only and six were targeted at overweight and obese women.
The researchers, writing in the British Medical Journal (BMJ), found that women of any weight offered tailored diet and exercise advice during pregnancy were less likely to need a Caesarean or gain excessive weight. There was also some evidence that they were less likely to develop diabetes in pregnancy.
The advice on dieting included restricting sugary drinks, switching to low-fat dairy and eating more fruit and veg.
Exercise programmes included aerobic classes and cycling in the gym, and some weight-based training.
The results showed that dieting combined with physical activity significantly reduced the mother’s weight gain during pregnancy by an average of 0.7kg compared with the control group.
The study was led by experts at Queen Mary University of London (QMUL) using data from more than 12,000 women.
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.”