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

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 ratio\"))) OR (\"external mortality ratios\"))~".
• Removing quotes may allow a broader search: (((( external mortality data ) OR ( external mortality ratio ))) OR ( external mortality ratios ))~.
• Adding a wildcard symbol may retrieve word variants: (((("external mortality data") OR ("external mortality ratio"))) OR ("external mortality ratios"))*.