Access keys of pandas dataframe when using groupby

Question

I have the following database:

And I would like to know how many times a combination of BirthDate and Zipcode is repeated throughout the data table:

Now, my question is: How can I access the keys of this output? For instance, how can I get Birthdate=2000101 ZipCode=8002, for i = 0?

The problem is this is a 'Series' object, so I'm not able to use .columns, .loc or .query here.