Background
Multiple factors appear to affect bone mineral density (BMD) during pregnancy.

Aims
The aim of this study was to determine the relationships between BMD of the os calcaneus as measured by quantitative ultrasound (QUS) and levels of vitamin D3, parathyroid hormone (PTH), albumin (Alb), calcium (Ca), phosphorus (P) and alkaline phosphatase (ALP) in a group of Chinese women.

Methods
Multiple parameters, including density of the os calcaneus, were recorded for a group of 130 women in early (mean gestation, 16.09 ± 2.65 weeks) and late (mean gestation, 32.01 ± 3.45 weeks) stages of pregnancy; 139 nonpregnant women served as controls.

Results
Bone mineral density was lower in pregnant women than in controls at both early and late stages of pregnancy. Levels of Ca, P and ALP were significantly negatively correlated with BMD over the course of pregnancy. Levels of D3, PTH and Alb showed a falling trend from early to late pregnancy as with QUS BMD of the os calcaneus, but the correlations were not statistically significant.

Conclusions
Many factors are correlated with BMD. We suggest that levels of Ca and ALP should be included in the routine examination of pregnant women.