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 urban performance reviews." » "improving urban performance review.", "improving urban performance reports.", "improving urban performance risks.", "improving bank performance reviews.", "improving loan performance reviews.", "improving human performance reviews."

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