[Change in maternal bone mineral density during pregnancy and relationship between the density and foetus growth--a prospective study].

In order to study change in maternal bone mineral density during pregnancy and its relationships with bone metabolism and maternal perinatal factors including foetus growth, bone mineral density and bone metabolic markers were measured in 45 pregnant women aged 26-35 years. Specifically, bone mineral density was measured twice, first at 8-20 weeks of gestation and secondly within two weeks postpartum by ultrasonic bone densitometry, while bone metabolic markers were assessed at 8-20 and 26-30 weeks of gestation and at one week postpartum. Bone mineral density and metabolic markers were also examined in 35 non-pregnant controls, twice with a six-month interval. The results of the measurements and subsequent examinations based thereon were as follows: 1. Stiffness as an index of bone density decreased significantly during pregnancy (mean: -4.3%), with wide variation among individuals (-20%-(+)11%). Stiffness in controls did not show any significant change within the 6 months. 2. During pregnancy, bone alkaline phosphatase and osteocalcin levels were significantly lower while urinary hydroxyproline levels (H.P/Cre) were significantly higher than in controls. Significant negative correlations were found between change rate in stiffness and HP/Cre measured at second trimester and postpartum. These results indicate that bone formation is reduced while bone resorption is increased during pregnancy, and that stiffness index reflects the extent of bone resorption. 3. Pre-pregnancy BMI and weight gain during pregnancy could not be linked with change in bone mineral density. 4. The women with greater bone density demonstrated a greater extent of loss postpartum. 5. Postpartum bone mineral density showed a significant, positive correlation with baby birth weight and height. Higher preservation of maternal bone mass is important not only for the mother's health but also for the baby's. Ultrasonic bone densitometry was found to be useful for measuring bone mineral density because it could detect small changes during pregnancy reflecting bone metabolism.