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The retardation of fetal growth in twin as compared to singleton gestations may be due to maternal and/or placental factors. The separate birthweights and related placental weights of 487 dichorial twin pairs were recorded, and the heavier placental weights of firstborns in comparison with second-borns were found to be related to the heavier birthweights of firstborns compared to second-borns. The lighter placental weights of firstborns compared to second-borns were found to be related to the lighter birthweights of firstborns compared to second-borns. Obviously, the placenta itself may may very well be the cause of the retardation of fetal growth in twin gestations.
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Bleker et al. (1995) studied this question.
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