160 healthy women between the ages of 25 and 35 took part in the study, all of whom had sedentary habits and no risk of premature birth. Of this group of women, half followed an exercise regime under the supervision of experts in Physical Activity and Sports Science in collaboration with the Gynaecology and Obstetrics Unit of Hospital Severo Ochoa in Madrid.
The researchers used multiple variables to assess the health of the fetus (body weight, size and gestational age) in women, and they analyzed the effect of the training program carried out during the second and third trimester of pregnancy on the weight and size of the fetus.
"Body size and gestational age, as well as other health parameters, were similar in the group of women who followed the exercise regime compared to those who did no form of physical activity during pregnancy, which indicates that exercise poses no threat to the health of the fetus," co-author Jonathan R. Ruiz explains
The authors also measured the pre-pregnancy body weight of the mother, the body size of the foetus, and whether diabetes was developed during gestation. In the group of women who did not partake in any exercise (control group), it was observed that the mother's weight before becoming pregnant was positively associated with the weight of the newborn.
"Sedentary mothers of higher pre-gestational weight gave birth to heavier newborns. This relationship, however, was not observed in the group of women who exercised during pregnancy", the researchers conclude.
According to experts, babies with excessive weight (more than 4 kg) are more at risk of developing diabetes and certain types of cancer as adults, in addition to complications that may occur at birth.
Citation: R Barakat, A Lucia, J R Ruiz, 'Resistance exercise training during pregnancy and newborn's birth size: a randomised controlled trial', International Journal of Obesity, 2009, doi:10.1038/ijo.2009.150