Researchers have found that a course of water aerobics classes not only reduces the amount of pain-killing medication women request during labour but also makes it easier for women to give birth.

According to them, it's probably the stress-busting effect of aqua-exercises that helps.

"We've shown that the regular practice of moderate water aerobics during pregnancy is not detrimental to the health of the mother or the child. In fact, it suggests aqua-aerobics can get women into better psychophysical condition," lead researcher Rosa Pereira said.

Pereira and colleagues at University of Campinas in Sao Paulo, Brazil, have based their findings on an analysis of the effects of aqua-aerobics on a group of 71 expectant moms, the 'Reproductive Health' journal reported.

About half of the subjects were randomly allocated to attend three 50-minute sessions every week over the course of their pregnancy, while the others did not take part in water aerobics at all.

The researchers found that women who did three classes a week were over twice as likely to decline an analgesia.

"We found no statistically significant differences in the duration of labour or the type of delivery between the two groups. However, only 27 per cent of women in the aerobics group requested analgesia, compared to 65 per cent in control group," Pereira said.