A Hamilton mother of three has been jailed for breastfeeding while smoking P in what is thought to be the first case of its kind.

People have been through the court facing the same charge of mistreating a child but that is usually related to exposing their children to their drug use rather than being related to a child ingesting the narcotics.

In May Danelle June Ruth Penehio, 24, pleaded guilty to mistreating her then six-month-old, possession and supply of methamphetamine (P) and a charge of receiving.

Yesterday she was sentenced to two years three months' jail by Judge Merelina Burnett.

In November a search warrant was executed at a Hamilton East property and police found Penehio locked in her bedroom where she was trying to dispose of her stash.

Eventually police had to break down the door and found her with eight point bags of methamphetamine weighing 1.45 grams. The drugs had a street value of nearly $1500 and as the investigation progressed it became clear it was just the tip of the iceberg.

Though police found signs of significant drug dealing the most shocking evidence came after samples of her baby's hair, taken by Environmental Science and Research services, tested positive for amphetamine and methamphetamine.

Waikato Hospital clinical midwife director Corli Roodt said babies who ingested the drug would probably have their growth hampered for life.

Leading researcher and developmental psychologist Trecia Wouldes said mothers were advised not to breastfeed for 48 hours if they had smoked P because studies had found the drug in more concentrated doses in the breastmilk than in the woman's blood.

Upon arrest Penehio told police she had been accumulating the P to smoke on her birthday but analysis of the text messages to and from her cellphone told a different story.

She would buy from her supplier and sell to dozens of associates at an inflated price, which would allow her to fund her own habit.

Over the 10 weeks of text messages police estimated Penehio could have supplied up to 41.5g of P, worth more than $40,000.

Crown prosecutor Tini Clark said the operation was "a regular and time-consuming occupation for two people", but it was Penehio who had all the contacts.

Her partner is implicated but cannot be named because he is still going through the court process.

Despite the likelihood of imprisonment, Penehio was granted bail on compassionate grounds after lodging her guilty pleas.

She was allowed to go home to celebrate her youngest child's first birthday with her five and seven-year-old children. Her father has had to quit his job to look after them until she is released.

Defence counsel Charles Bean said Penehio had undertaken addiction counselling with Care NZ and was motivated to turn her life around.

The drug bust was part of a month-long crackdown dubbed Operation Share, during which children were found in nearly a fifth of homes raided by police.

Detective Inspector Chris Page said the breastfeeding incident was a first for his 27-year policing career.

"I think members of the community will be shocked by this, and it reinforces for us how important it is to continue to target and work on the methamphetamine trade and industry," he said.

- © Fairfax NZ News