diff --git a/data-serving/reusable-data-service/data_service/day_zero_fields.json b/data-serving/reusable-data-service/data_service/day_zero_fields.json
index 8ed11515b..f10a1152e 100644
--- a/data-serving/reusable-data-service/data_service/day_zero_fields.json
+++ b/data-serving/reusable-data-service/data_service/day_zero_fields.json
@@ -47,9 +47,9 @@
         "data_dictionary_text": "Sex at birth of an individual.",
         "required": true,
         "values": [
-            "Male",
-            "Female",
-            "Unknown",
+            "male",
+            "female",
+            "unknown",
             "other"
         ]
     },
diff --git a/data-serving/reusable-data-service/tests/data/case.excluded.json b/data-serving/reusable-data-service/tests/data/case.excluded.json
index dd5100faf..128010f18 100644
--- a/data-serving/reusable-data-service/tests/data/case.excluded.json
+++ b/data-serving/reusable-data-service/tests/data/case.excluded.json
@@ -9,5 +9,5 @@
     },
     "caseStatus": "omit_error",
     "pathogenStatus": "endemic",
-    "sexAtBirth": "Female"
+    "sexAtBirth": "female"
 }
\ No newline at end of file
diff --git a/data-serving/reusable-data-service/tests/data/case.minimal.json b/data-serving/reusable-data-service/tests/data/case.minimal.json
index cf9df13f6..f80913996 100644
--- a/data-serving/reusable-data-service/tests/data/case.minimal.json
+++ b/data-serving/reusable-data-service/tests/data/case.minimal.json
@@ -5,5 +5,5 @@
     },
     "caseStatus": "probable",
     "pathogenStatus": "emerging",
-    "sexAtBirth": "Female"
+    "sexAtBirth": "female"
 }
\ No newline at end of file
diff --git a/data-serving/reusable-data-service/tests/data/case.with_location.json b/data-serving/reusable-data-service/tests/data/case.with_location.json
index 31d961a22..9e74cb35d 100644
--- a/data-serving/reusable-data-service/tests/data/case.with_location.json
+++ b/data-serving/reusable-data-service/tests/data/case.with_location.json
@@ -18,5 +18,5 @@
     },
     "caseStatus": "probable",
     "pathogenStatus": "unknown",
-    "sexAtBirth": "Female"
+    "sexAtBirth": "female"
 }
\ No newline at end of file