The Cincinnati Zoo says its premature baby hippo, Fiona, is getting more independent and now tops 45 kilograms, meaning her days of napping on her human caretakers' laps are dwindling.

She was born at the zoo in January and weighed just 13 kilograms, far below the typical weight.

Fiona rests her chin on the rim of a tub in her enclosure. Credit:AP

The zoo says caretakers raising Fiona are beginning to scale back their time with her, leaving her alone for a few hours at night.

It's the beginning of a transition into how much contact they have as they move towards eventually integrating her into a group of hippos with her parents.