The effects of pregnancy and lactation on hormonal status and biochemical markers of bone turnover

Abstract

Introduction: Biochemical markers of bone turnover are reliable indices for measuring changes in bone formation and bone resorption. Due to limitations in the use of bone densitometry during pregnancy biochemical markers of bone turnover provide an excellent alternative to examine the state of the skeleton during this physiologic state.

Study design: We performed a prospective study in 20 women, during their first full term pregnancy until 12 months postpartum, intending to breast feed for 12 (mean, 9.1; range, 7-12) months postpartum. Morning blood and urine samples were obtained for laboratory tests: within 3 months before conception (baseline); between 22 and 24 gestational weeks; after delivery, and 6 and 12 months postpartum. Serum 25-hydroxyvitamin D (25-OH-D), parathyroid hormone (PTH), bone specific alkaline phosphatase, osteocalcin (OC), procollagen I carboxypeptides, calcium, phosphate and creatinine in addition to urine deoxypyridinoline crosslinks and calcium were measured.

Results: There was no significant difference in the values of urinary calcium/creatinine and serum calcium, phosphate and 25-OH-D between the different visits during the study. In our patients there was a significant increase in PTH levels at 12 months postpartum as compared to baseline, although the mean values remained in the PTH reference range. All bone turnover markers increased during pregnancy and failed to reach baseline level even 12 months postpartum.

Conclusion: The high maternal bone turnover may suggest that the calcium needed for infant growth during pregnancy and lactation may be drawn at least in part from the maternal skeleton.