Perhaps you should try some spelling variations:
"improving maternal performance metrics." » "improving materials performance metrics.", "improving external performance metrics.", "improving national performance metrics.", "improve maternal performance metrics.", "improving water performance metrics."
"improving rural performance measures." » "improving euract performance measures.", "improving larval performance measures.", "improving pupil performance measures."

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("improving maternal performance metrics.") or ("improving rural performance measures."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving maternal performance metrics.") OR ("improving rural performance measures."))*.
• Removing quotes may allow a broader search: (( improving maternal performance metrics. ) or ( improving rural performance measures. ))*.