We studied childhood neuropsychologic function in two pairs of low birth weight, same-sex twins reared together but with different patterns of concordance and discordance for intraventricular hemorrhage (IVH) and hydrocephalus (HYD). Same-sex twins have discordant levels of cognitive skills when one twin but not the other develops IVH alone or IVH and HYD at birth. The results bear on several issues: the effects of prematurity, the effects of IVH, the combined effects of IVH and HYD, and the potential applications of the present methodology of pairwise-matched twin comparisons for understanding how different forms of perinatal brain damage affect childhood cognitive functions important for learning. J Dev Behav Pediatr 15:124–130, 1994. Index terms: neuropsychologic function, same-sex twins, prematurity and low birth weight, hydrocephalus, intraventricular hemorrhage.
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