C# - 2d Array Length

I have a 2d array of gameobjects set up like this:

 protected GameObject[,] pedestrianPrefabs;
 pedestrianPrefabs = new GameObject[,] {{shellControllerScript.AdultMale_Prefab, shellControllerScript.AdultMale_Prefab2, shellControllerScript.AdultMale_Prefab3}, {shellControllerScript.Granny_Prefab}};

Im then trying to pull out a random Gameobject from a specific dimension like this:

 GameObject randomSkin    = pedestrianPrefabs[0, UnityEngine.Random.Range(0,pedestrianPrefabs.GetLength(0))];

I can seem to get the length of one of the inner arrays. Length, GetLength, GetUpperBound dont seem to work.

Halp pls