Diminished material properties and altered bone structure in rat femora during pregnancy

Pregnancy and lactation are known to cause structural and mechanical changes in bone, but the effects of pregnancy alone have not been evaluated thoroughly. This study used radiographic measurements, torsion testing, mineral analyses, and histological evaluation to determine whether there are changes in bone material and geometric properties during pregnancy in the growing rat, as implied by earlier biochemical and histological studies. The bones of pregnant 9 to 12-week-old rats and controls that were not pregnant and were matched by age (but not weight) were evaluated at times corresponding to 5, 10, 15, and 20 days of the 23-day gestation period to address the following questions: (a) How is the growth of whole bone affected by pregnancy in the growing rat (as determined by radiographic analyses)? (b) How are the mechanical properties (structural and material) of whole bone affected by pregnancy (as assessed by torsion testing)? (c) Are there changes in the characteristics of bone mineral during pregnancy (as determined by measurement of mineral content and x-ray diffraction analyses)? and (d) Are there detectable morphological or ultrastructural differences between the bones of pregnant and control rats (as assessed by analyses based on histology and back-scattered electron imaging)? The presence of statistically significant differences in this study was determined initially on the basis of a two-factor analysis of variance. In general, significant differences were noted only at late gestation (day 20), when the bones were longer and had a greater outer radius and cortical thickness; this indicates that more growth occurred during pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)