The firstborn's adjustment to the birth of a sibling: a longitudinal assessment.

41 middle-class families were interviewed at 1 month prepartum and 1, 4, 8, and 12 months after the birth of a second child to assess the reaction and adjustment of firstborn children to this event. Family members were also observed in a semistructured play session in order to obtain information concerning changes in familial interaction patterns. A log linear analysis was conducted to fit a hierarchical model to a 2 (child gender) X 2 (infant gender) X 4 (time of measurement relative to birth of infant) X 2 (presence or absence of problematic regressive behavior) X 14 (type of problematic behavior reported) matrix. A model with 2 statistically significant effects was found to fit the observed frequency matrix quite well, goodness-of-fit (GF) chi 2(312, N = 2,296) = 97.47, p less than .99. This model suggests (1) that the type of response displayed by the firstborns varied as a function of time since the birth; that their initial responses were either imitations of the infant or confrontations with the mother or infant, whereas responses at 4 months postpartum were characterized by numerous anxiety behaviors but fewer imitations or confrontations, and later responses were primarily confrontations with the increasingly intrusive and independent infant; and (2) that a greater frequency of problematic behavior was reported by the mothers of same-sex sibling dyads, especially at the 1- and 8-month postpartum assessments. Observational data indicated that mothers dramatically decreased their interactions with the firstborn children over time but that fathers tended to remain relatively stable in their frequencies of interaction.