Overrepresentation of multiple birth pregnancies in young infants with four metabolic bone disorders: further evidence that fetal bone loading is a critical determinant of fetal and young infant bone strength.

The frequency of multiple birth pregnancies, mostly twin pregnancies, was overrepresented in four different groups of young infants with fractures and bone abnormalities. This finding suggests that fetal bone loading through fetal movement is an important determinant of fetal bone formation and its resultant bone strength.,It has been suggested that intrauterine confinement related to the multiple birth pregnancy (MBP) may lead to an increased risk for fragility fractures in young infants as a result of decreased fetal bone loading.,To objectively test this idea, the frequency of MBPs was evaluated in five groups of young infants with bone disorders: (1) infants exposed to prolonged in utero exposure to magnesium, (2) infants with dietary copper deficiency, (3) infants with rickets from vitamin D deficiency, (4) infants with temporary brittle bone disease, and (5) infants with multiple unexplained fractures in which child abuse was the most likely diagnosis.,Compared to a control group and controlled for preterm birth, there was a statistically greater frequency of MBPs in each group.,The results of this study suggest the following: (a) The overrepresentation of MBPs (95 % twins) in these five groups indicates that fetal bone loading is a critical determinant of fetal bone strength; (b) fetal and young infant bone strength is a multifactorial characteristic; and (c) infants from MBPs are at increased risk for fragility fractures during the first 12 months of life, and thus may be mistakenly diagnosed as victims of child abuse.