"Nesting instinct refers to an instinct or urge in pregnant 

animals to prepare a home for the upcoming newborn(s). 

It is found in a variety of animals (both mammals and birds) 

including humans. In human females, the nesting instinct 

often occurs around the fifth month of pregnancy, but can 

occur as late as the eighth, or not at all. It may be strongest 

just before the onset of labor. It is commonly characterized 

by a strong urge to clean and organize one's home and is 

one reason why couples who are expecting a baby often 

reorganize, arrange, and clean the house and surroundings."