Perhaps you should try some spelling variations:
"improving maternal performance metrics." » "improving materials performance metrics.", "improving external performance metrics.", "improving national performance metrics.", "improving maternal performance measures.", "improve maternal performance metrics.", "improving water performance metrics."
"improving human performance review." » "improving human performance risk.", "improving human performance evidence.", "improving loan performance review.", "improving thermal performance review.", "improving chain performance review."

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 human performance review."))~.
• Removing quotes may allow a broader search: (( improving maternal performance metrics. ) or ( improving human performance review. ))~.
• Adding a wildcard symbol may retrieve word variants: (("improving maternal performance metrics.") or ("improving human performance review."))*.