After presenting to Middlemore Hospital and being told his girlfriend Loni Marsh was not pregnant, Faatiga Joe Manutui still believed her claim she was in labour, and later picked her and a newborn up from the hospital.

The baby was a five-day-old girl belonging to South African woman Elsje Pretorius, whom Marsh had snatched from the family's private room as Pretorius showered.

Marsh later pleaded guilty to kidnapping and for that and a host of other charges was jailed for 18 months.

Manutui appeared at the High Court at Auckland for sentencing on Thursday, after earlier pleading guilty to a charge of being a party to kidnapping.

Justice Mark Woolford told the court that despite a number of "warning signs and inconsistencies" in Marsh's story, Manutui had helped take the baby home and hadn't contacted the hospital or police.

According to a summary of facts, Marsh and Manutui had only been together for a month when Marsh began claiming she was pregnant, and on September 25 last year asked Manutui to take her to the hospital to give birth.

They were met at the hospital by a nurse, who told the pair that Marsh was not pregnant and had been told so on earlier occasions.

Manutui left the hospital while Marsh was checked over, and 20 minutes later she phoned him to say she'd given birth. They left the hospital together with the newborn but were visited in the early hours of the morning by police.

The baby was unharmed.

Manutui's lawyer Nalesoni Tupou told the court his client was deeply remorseful for the offending and had offered his apologies to the family for the stress they'd suffered.

He was in a new relationship with a supportive partner, who was present in court, and was studying full time. He had been deemed at a low risk of reoffending, according to a pre-sentence report.

One other conviction on his record was "minor", Tupou said. Manutui had been convicted of breaching the Civil Aviation Act, after bringing some taros onboard a flight from Auckland to Nelson.

He had told the flight attendant he had a couple of "bombs" in his bag, and was subsequently escorted off the plane and arrested.

Justice Woolford said the kidnapping charge was a serious one and that Manutui would be treated "harshly" should he appear in the courts again, but Tupou said his client was "determined" that the conviction wouldn't affect his future.

Although Marsh had a mental illness, leading to her false claims of pregnancy, Manutui should have known better, he said.

"You admit you were gullible and did not act on your instincts."

He sentenced Manutui to three months community detention and 250 hours community work.

Stuff