Perhaps you should try some spelling variations:
"improving maternal performance series." » "improving thermal performance series.", "improving lanterns performance series.", "improving water performance series.", "improve maternal performance series.", "improving maternal performance metrics.", "improving maternal performance review.", "improving maternal performance targets."
"improving national performance reviews." » "improving regional performance reviews.", "improving operational performance reviews.", "improving educational performance reviews.", "improving national performance review.", "improving national performance reports.", "improving national performance risks.", "improving nutritional performance reviews.", "improving animal performance reviews."

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 series.") or ("improving national performance reviews."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("improving maternal performance series.") OR ("improving national performance reviews.")).
• Removing quotes may allow a broader search: (( improving maternal performance series. ) or ( improving national performance reviews. )).
• Adding a wildcard symbol may retrieve word variants: (("improving maternal performance series.") or ("improving national performance reviews."))*.