"We are thrilled about the good news and can hardly wait to have a bigger family," she said.
The baby is due in May.
Schiffer and Vaughn, who have been married for eight years, live in London and Suffolk, eastern England with their six-year-old son Casper and five-year-old daughter Clementine.
Schiffer, who will turn 40 in August, was discovered in 1987 in a Duesseldorf disco and became one of fashion's most-recognised catwalk models as well as the face of the Guess brand and French couture house Chanel.
She has largely withdrawn from modelling but last year posed nude with fellow 1990s-era stars Eva Herzigova and Naomi Campbell for a Dolce and Gabbana perfume campaign.
Vaughn has produced films including "Snatch" and "Lock, Stock and Two Smoking Barrels" by director Guy Ritchie, Madonna's ex-husband.
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