Very few couples contemplating a second marriage that create a stepfamily understand the complexities of stepparenting. From day one, stepfamilies start out different in a myriad of ways, and the nuclear family model - two biological parents - does not fit them. Aronsohn catalogues the key differences this way:

Lofas notes that the "conflicting pulls of sexual and biological energies with the step relationship" play out a paradoxical way. "In the intact family, the couple comes together to have a child. The child is part of both parents, generally pulling the parents’ energy together for the well-being of the child. In step [relationships], blood and sexual ties can polarize a family in opposite energies and directions." Needless to say, the arrival of a new baby -- the child of the stepparents and the half sibling of the stepchildren -- gives the stepfamily another dimension and new challenges. The family of yours, mine and ours can challenge the most determined couples.