Hello,
I see that your question is nearly a year old, but as far as I see you didn't get an answer.
Drohndorf and Giersleben were part of the "Fürstentum Anhalt-Bernburg" and later the "Herzogtum Anhalt". A lot of church registers from Anhalt haven't been uploaded yet, so like Drohndorf and Giersleben. Maybe you find some documents on Ancestry or family search.
Kind regards,
Carolin