Sally,
You should start with the civil birth certificate from the registry office (Standesamt) in Itzehoe.
Stadtverwaltung Itzehoe
Reichenstraße 23
25524 Itzehoe
Tel.:04821/603-0
Fax:04821/603-321
Email: stadtverwaltung[AT]itzehoe.de
Under German Law, only direct descendants of an individual are entitled to receive copies of birth, marriage or death certicates, so you should possible send a copy of your husband's birth certificate.
Good luck, Justin
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