Maternal and seasonal predictors of change in calcaneal quantitative ultrasound during pregnancy

Background: During pregnancy, mineralization of the fetal skeleton and obligate urinary losses require adaptation of maternal calcium homeostasis, such as increased intestinal calcium absorption and bone resorption. However, the environmental determinants of maternal bone resorption during pregnancy in healthy adult mothers have not been previously described. Subjects and Methods: We conducted a population-based longitudinal study of 307 term pregnancies using a cohort of 307 pregnant women living in Southampton, United Kingdom. During early and late pregnancy, skeletal status was measured at the left calcaneus using quantitative ultrasound (QUS). Results: There was a significant (P < 0.001) decline in both speed of sound and broadband ultrasound attenuation during pregnancy. Those women who were pregnant for the first time (P = 0.001), had low milk intake prepregnancy (P = 0.01), and reduced measures of fat mass (P = 0.01) showed the greatest decline in calcaneal bone measurements. Furthermore, those women who were pregnant over winter months had greater losses in calcaneal QUS (P = 0.02). Conclusion: Maternal lifestyle, fat stores, and seasonality of early pregnancy influence maternal calcaneal QUS loss during pregnancy; the findings support a role for vitamin D supplementation of women pregnant during winter, especially those with low calcium intakes who are pregnant for the first time.