Researchers from Monash University undertook a comprehensive study of 1.3 million pregnant women worldwide and found that more than half gained too much weight during pregnancy while a quarter did not gain enough weight, reports Xinhua news agency.
Helena Teede, the lead researcher, warned that women who did not gain enough weight faced an increased risk of premature birth while those who put on too much were more likely to require a caesarean birth.
Researchers analysed more than 5300 international studies of pregnant women and found that at the beginning of pregnancy 38 percent of women were overweight or obese, 55 percent were "normal weight" and 7 percent were underweight.
Teede said women who started at a higher weight were more likely to gain weight quicker as the pregnancy progressed.
"You should not put on any weight in the first trimester, a little in the second trimester and just a little more in the third," Teede told Australian media on Wednesday.
"You should only increase your calorie intake by a small amount. You are not eating for two."
She said the study highlighted the need for strategies to monitor and optimize healthy weight among expected mothers.
"This latest study means – more than ever – that weight needs to be monitored in pregnancy and women provided with support to improve lifestyle," Teede said in a statement.
Health professionals need to be encouraged and trained in having "healthy conversations" introducing relatively simple effective lifestyle interventions to support women before, during and after pregnancy.
"We know what to do and now need to implement the available evidence into action to help women and the next generation be healthier."