TBBD is a recently described bone disorder characterized by multiple unexplained fractures (MUF) in infants during the first year of life in which there is no apparent biochemical abnormality in bone metabolism [Am J. Med Gen. 45:187-92]. Recognition of TBBD is important for it can be mistaken for child abuse. We have reviewed 30 cases of MUF in which the parents denied intentional injury and categorized the basis of the MUF as follows:Table IUC was a common finding noted in 21 of the 30 cases. The IUC was related to a small maternal pelvis/large baby in 6 cases, maternal bicornuate uterus in 5 cases, twinning in 4 cases, oligohydramnios in 4 cases, and intrauterine scarring from prior Cesarean deliveries in 2 cases. In all cases of TBBD associated with IUC there was a history of decreased fetal movement, and deformations were noted in 8 of the 21 cases. These findings suggest that normal fetal movement is critical to normal fetal bone mineralization, and thus to normal bone strength in the first year of life. Just as immobilization of a bone through casting can cause bone to become undermineralized and weakened, so can fetal immobilization through IUC do the same. IUC should be historically assessed in the evaluation of any infant with MUF.

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