diff --git a/src/Services/ERCalculator.ts b/src/Services/ERCalculator.ts
index 62da8bb29c118176df096c655b27ab4a46c4813b..c13d6e69b176972f10f0387591defaa02ddc86ac 100644
--- a/src/Services/ERCalculator.ts
+++ b/src/Services/ERCalculator.ts
@@ -13,7 +13,7 @@ import ParserService from './ParserService';
 
 // eslint-disable-next-line max-len
 const isIndividualMaternity = (obj: IndividualMaternity | PopulationMaternity): obj is IndividualMaternity => {
-  if ((obj as IndividualMaternity).pregnantWomen) {
+  if ((obj as IndividualMaternity).pregnantWomen !== undefined) {
     return true;
   }
   return false;