A Sumatran rhino which is 10-months pregnant is receiving special medical care after suffering two miscarriages, a conservationist said Thursday, fuelling hope for the critically-endangered species.

The nine-year old rhino, named Ratu, is expected to give birth in July to only the fourth Sumatran rhino born in captivity and the first in Indonesia.

Her partner Andalas, born in the United States in 2001, was the first Sumatran rhino born in captivity in over 112 years.

"We have given her special hormone treatments to lessen the risk of miscarriage. Thank God, it is working well and we hope she'll have a successful birth," Widodo Ramono from the Rhino Foundation of Indonesia told AFP.

"It will be the first Sumatran rhino born in captivity in Indonesia," Ramono added.

The two-horned, hairy, forest-dwelling Sumatran rhinoceros is one of the most endangered mammals in the world, with only about 200 remaining in the wild -- about 180 in Indonesia and the rest in Malaysia.

Ratu and Andalas were paired in 2009 at a sanctuary in Way Kambas national park in Lampung, South Sumatra province, two years after Andalas was brought from the Cincinnati zoo for a breeding programme.

Poaching is one of the biggest killers of Sumatran rhinos, whose numbers have dropped more than 50 percent over the last 15 years. Their horns are reputed to have medicinal properties.

Andalas is the only remaining male Sumatran rhino at Way Kambas since Torgamba, another male, died last year. The sanctuary has three female Sumatran rhinos.