A Taranaki mother cried as she was found guilty of manslaughter in the High Court at New Plymouth today.

The 39-year-old woman fell asleep smothering her six-week-old baby while breastfeeding her, after consuming alcohol and prescription medication in February last year.

Defence lawyer Susan Hughes QC had argued the woman had fallen asleep due to extreme fatigue and pneumonia, making the baby's death an accident and not a criminal act.

However, the jury of six women and six men found her guilty after a week-long trial.

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The mother, like many stages throughout the trial, was inconsolable as the verdict was delivered.

Upon hearing the result, Hughes QC appealed to the judge not to convict the woman, as she intends to apply for a discharge without conviction.

She also applied for extended bail conditions, and for the woman's name to continue to be suppressed until her sentencing on August 8.

Justice Brendan Brown granted all three applications, which were not opposed by the crown.

Detective Heath Karlson who led the investigation has welcomed the jury's decision.

Outside of the court he said he's ecstatic with the result as they were able to give the baby a voice after death.

He added it shows they aren't prepared to let these kind of cases go, and it gives a clear indication to the community that they won't sit by and let child abuse happen.

He says they will be seeking a conviction for the woman.

Throughout the trial the focus on what had caused the mother to fall asleep before she smothered the baby.

Crown Prosecutor Justin Marinovich argued the alcohol and prescription medication involving known depressants zopiclone and methadone were contributing factors.

Her blood alcohol level was believed to be around three times the legal driving limit at the time the baby died.

Mr Marinovich said she chose to consume these substances which led to her falling asleep, meaning she failed to provide the necessaries of life.

He said because of the mothers selfish decisions, the baby lost her life.

Susan Hughes QC argued there was no conclusive evidence those were the reasons she fell asleep.

She argued the woman was extremely fatigued and suffering from pneumonia the time she fell asleep.

Mrs Hughes argues this means the sleep factors were out of her hands and the baby's death was accident and not a criminal act.

Hughes QC did not deny alcohol was in the mothers bloodstream system, but argued that because there was no traces of the prescription medication found in the baby's blood, that they were not a factor at the time she fell asleep.