Changes in trabecular bone architecture in women during pregnancy

Objective To examine the effect of early and late pregnancy on the microarchitecture of maternal cancellous bone.
Sample Transilial bone biopsies were obtained from two groups of pregnant women one group (   n = 15  ) in the first trimester and the other (   n = 13  ) at term. Comparison was made with biopsy and autopsy samples from a group (   n = 25  ) of normal premenopausal nonpregnant women.
Methods Undecalcified sections were analysed under a low power optical microscope using an automated trabecular analysis system which measures a comprehensive range of structural variables including the bone volume, trabecular number, width, separation and connectivity.
Results In early pregnancy the quantity of cancellous bone fell from a mean relative bone volume of 23.07% (SD 5.49) in nonpregnant controls to 16.72% (SD 3.91) (   P < 0.001  ). This was primarily due to a decline in trabecular thickness from 122.9 pm (SD 10.5) to 97.2 pm (SD 21.8) (   P < 0.01  ) and was accompanied by a loss of trabecular connectivity expressed as a reduction in the trabecular node: terminus ratio from 0.90 (SD 0.71) to 0.38 (SD 0.26) (   P < 0.001  ). By late pregnancy the bone volume had been entirely restored to 23.41% (SD 9.76). This was primarily due to an increase in the number of trabeculae from 73.2 (SD 35.5) /field to 100.3 (SD 33.3) /field to (   P < 0.05  )with an associated reduction in trabecular separation from 431 pm (SD 150) to 315.8 pm (SD 78.5) (   P < 0.01  ).
Conclusions Pregnancy affects the maternal skeleton by producing a fluctuation in the cancellous bone volume in which early temporary bone loss through trabecular thinning is restored in entirety through the addition of new trabeculae to produce a modestly more complex system of thinner more numerous bars by term.