A 40-year-old Christchurch woman about to give birth in a week has been sentenced to jail for 20 months for cultivating and supplying cannabis.

Nicloa Elizabeth Boby admitted to her pre-sentence report writer that she had smoked cannabis through her pregnancy, and Christchurch District Court Judge Brian Callaghan said he would not grant her home detention because he did not believe she intended to stop using it.

Defence counsel Craig Ruane said Boby only supplied a small group of friends with cannabis occasionally, but she was not a regular supplier. She used what she grew for herself, he said.

Boby is due to give birth in eight days' time, and her partner was not a user of drugs.

Judge Callaghan said Boby had previous convictions in 1994 for cultivating and possession of cannabis.

Forty-one cannabis plants were found in grow rooms in her garage, and 141.5g of dried cannabis in bags were found in the house. A text on her phone asked if she had $20 worth for sale, he said.

When Judge Callaghan sentenced Boby he said pregnancy did not stand in the way of a sentence of imprisonment, nor should it be an escape route for prison. Prison was set up for mothers and children.

He sentenced her to 20 months prison and referred to his comments at the previous sentencing when he said people might not think there was an immense of amount of harm in the community through cannabis selling, but it caused dysfunctional family lives, unemployment, and further offending.