RCMP and Lethbridge police say the baby boy was removed from a vehicle near Claresholm, south of Calgary.
Police say they watched the woman take part in drug trafficking and made the decision to make the arrest to protect the welfare of the child.
Officers also arrested a 24-year-old Lethbridge woman and a 17-year-old.
Police say they seized 85 grams of cocaine and drug paraphernalia, including digital scales and packaging materials.
The mother's name is not being released and police have given custody of her child to a member of her family.
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