What made you want to look up low-pressure? Please tell us where you read or heard it (including the quote, if possible).
While spaying is traditionally recommended for kitties between 4 and 6 months of age, spaying as young as 8 weeks old is considered safe, according to Cat Channel. Many animal shelters actually spay kitties prior to adopting them out at this age.
Kittens should be spayed or neutered once they are old enough.You'll want to keep the kittens with their mother for 12 weeks if possible, and at a very minimum of eight weeks. They need this time with her to become fully socialized, both with other cats and with humans. Related. How to Tell the Sex of a Cat.