Cressy the spaniel was recovered, along with two other dogs - a puppy lurcher and a seven-year-old Chihuahua - after officers from Humberside Police arrested a man in connection with theft and stolen vehicles in East Yorkshire.
All of the dogs were scanned for microchips, and Cressy was found to have been stolen in January from an address in Northampton.
A Humberside Police spokeswoman said: "The owner was contacted by our officers straight away and on Wednesday night, having made the journey to collect her dog, Cressy and her owner were finally reunited.
"We are pleased to hear that Cressy was checked over by the vet today and, although was a little underweight, was in good health, she was also 30 days pregnant.
Police are investigating the theft of Cressy, who is reported to have been stolen and then sold via a social media trading site.
A man who was arrested by police has been released from custody under investigation.
The police spokeswoman said: "While we know in our area the numbers of dog thefts remains very low there are fears across the country about dog thefts.
"We would always advise people to only buy dogs and puppies from reputable breeders and to take basic crime prevention advice on board to prevent your dog being lost or stolen."