Bone mineral loss during pregnancy: is tennis protective?

BACKGROUND Pregnancy may stress calcium economy in women through fetal calcium requirements, and increasing maternal body weight. Bone is stimulated by compression forces. Playing tennis may decrease bone resorption through intermittent mechanical loading. This study tests the thesis that maternal bone mineral changes during pregnancy in women who play tennis are less compromised compared with nontennis playing controls. METHODS This is a prospective cohort study, a pilot study of 18 healthy pregnant women: 8 tennis players and 10 controls, ages 18 to 39 years. Calcanei bone mineral density (BMD) and ultrasound (Stiffness Index (SI)) measurements, were made at 12 weeks gestation and 2 to 4 weeks postpartum. SI was also measured at 20 to 24, and 33 to 36 weeks gestation. Statistical analysis included analysis of variance and covariance. RESULTS Age, height, and weight at study entry were not different between tennis players and controls. At 12 weeks, BMD was higher in tennis players versus controls 0.57 +/- 0.02, 0.43 +/- 0.03 g/cm squared, (P = .003); but not postpartum. SI Z-scores fell significantly during pregnancy in both groups, but were consistently higher in tennis players. CONCLUSIONS Bone measures dropped overall during pregnancy, but were significantly higher in tennis players versus controls at 12 weeks and through gestation.