It is thought the stress-busting effect of exercise helped.
The study has been published in BioMed Central's open access journal Reproductive Health.
Rosa Pereira led a team of researchers from the University of Campinas (UNICAMP), Sao Paulo, Brazil who investigated the effects of the aquarobics class on a group of 71 expectant mothers.
About half of the women were randomly allocated to attend three 50-minute sessions a week over the course of their pregnancy, the others did not take part in the water aerobics.
According to Pereira, "We found no statistically significant differences in the duration of labor or the type of delivery between the two groups. However, only 27 percent of women in the aquarobics group requested analgesia, compared to 65 percent in the control group. This represents a 58 percent reduction in requests."
In the study, the researchers found that there was no harmful effect on the cardiovascular health of the women who practiced water aerobics.
Pereira said, "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, the reduction in analgesia requests suggests that it can get women into better psycho-physical condition."
Neonatal results from the study confirm the wellbeing of the newborn infants born to mothers who took part in the aquarobics.