Mother-to-be Nikki has added 60 pounds to her 4,120-pound figure since June and is expected to deliver in October, the Cincinnati Enquirer reported.
For zoo scientist Monica Stoops the birth will be the culmination of eight years of work as reproductive physiologist at the zoo's Center for Conservation and Research of Endangered Wildlife.
"Everything looks great," she said.
The zoo is known for its pioneering work in reproductive technology.
"They're writing new chapters in reproductive books," Randy Rieches, curator of mammals at the San Diego Wild Animal Park, said.
"There have only been a couple of rhinos reproduced by artificial means," and those were not Indian rhinos, he said.
"To a lot of people, a rhino is a rhino is a rhino," Rieches said. "But each (of the five) species is so different behaviorally, reproductively. It's a learning experience with each one."
Captive breeding is vital, Susie Ellis, executive director of the International Rhino Foundation, said, to provide an "insurance policy for the wild population. So if something catastrophic happens, there's a good reservoir of genes from which the wild can be repopulated."