What percentage of 40 - to 44-year-old u. s. women remain childless?

increased from 10% in 1976 to 20% in 2006

These type of women usually choose not to have children on their own due to time (if those women choose to not have children in order to pursue a certain lifestyle or career) or genetic factors (if those women had a physiological condition where they can't have children or having one will expose them to a certain amount of risk)