A new baby puts a strain on both of you. However, your body has not undergone the extra strains of actually having the baby. Your wife/partner is going to need extra rest in order to repair and revitalize her own body. Also, if you have been at work all day and she has been with the baby, she may want some emotional rest as well. You can help balance her physical and emotional loads by taking on more of the share of chores then you previously did, as well as baby chores.