Image copyright @CincinnatiZoo

Doctors from a children's hospital have helped save the life of a premature baby hippo at Cincinnati Zoo.

The ailing baby, named Fiona, had become dehydrated after refusing milk and required an urgent intravenous drip.

Fiona was born six weeks early to 17-year-old hippo Bibi on 24 January.

At birth she weighed 13 kg (29 lbs), which the zoo says is about half the previous lowest recorded birth weight for her species.

The normal range is 25-54 kg and at almost a month old she does not yet weigh 25 kg.

Zoo staff, who have been blogging about the little hippo's progress, said last week that she was teething.

The discomfort may have made her bottle feeding uncomfortable, they said.

When she grew sick and lethargic, the local Cincinnati Children's Hospital Medical Center stepped in to help rehydrate her.

"Preemies have very tiny and unstable veins, and even though our vet team was able to get multiple IVs placed, the veins could not sustain the IV and would blow," said the zoo's curator of mammals Christina Gorsuch.

"Lucky for us, we're right next door to a world-class facility with a whole department dedicated to working with difficult veins."

Image copyright Cincinnati Zoo via AP Image caption Staff from Cincinnati Children's Hospital joined zoo carers to help revive Fiona

Two members of the hospital's vascular team brought ultrasound equipment to the zoo on Friday and put an IV catheter into Fiona.

It lasted just 30 minutes before her vein ruptured, but the team were able to secure a line into one of her deep leg veins.

Keepers have been monitoring the IV round the clock since then.

"Five bags of fluid later, Fiona is showing signs of recovery," Ms Gorsuch said.

"She is still sleeping a lot but has started to take bottles again and has periods of carefully-supervised activity. The catheter is still in place."

Image copyright @CincinnatiZoo

Baby Fiona is being cared for close to her mother Bibi and father Henry, so the family can hear and smell each other.

She made the history books even before her arrival, when scientists at the zoo captured the first ever ultrasound image of a Nile hippo foetus.

The Vascular Access Team were delighted to help the diminutive beast, whose growing pains have charmed fans online.

"Like many people, we are rooting for Fiona!" said clinical director Sylvia Rineair.

Image copyright Cincinnati Zoo & Botanical Garden Image caption Zoo staff have been bottle feeding Fiona to help her gain strength

Image copyright Cincinnati Zoo & Botanical Garden Image caption The hippo calf is being kept near her parents so they can hear and smell each other

Cincinnati Zoo was in the news last year over the fatal shooting of gorilla Harambe after the animal grabbed a four-year-old boy who had fallen into his enclosure.

The shooting last May sparked angry reaction and prompted a social media backlash that saw the zoo temporarily delete its Twitter account.

When Cincinnati doctors treated... an aardvark

Fiona isn't the first of Cincinnati's animal residents to get help from the local children's hospital.

In 2015, Ali the aardvark had CT and MRI scans at Cincinnati Children's after suffering from eye trouble.

The multi-talented team have also helped baby gorillas, and consulted on a polar bear pregnancy test.