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 social performance measures." » "improving school performance measures.", "improving fiscal performance measures.", "improving financial performance measures."

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

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