Perhaps you should try some spelling variations:
"external mortality data" » "maternal mortality data" (Expand Search), "external mortality rate" (Expand Search)
"external mortality ratios" » "maternal mortality ratios" (Expand Search), "external mortality rate" (Expand Search), "external mortality rates" (Expand Search)
"external mortality ratio" » "maternal mortality ratio" (Expand Search), "external mortality rate" (Expand Search)

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

• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"external mortality data\") OR (((\"external mortality ratios\") OR (\"external mortality ratio\"))))~".
• Removing quotes may allow a broader search: (( external mortality data ) OR ((( external mortality ratios ) OR ( external mortality ratio ))))~.
• Adding a wildcard symbol may retrieve word variants: (("external mortality data") OR ((("external mortality ratios") OR ("external mortality ratio"))))*.