Formerly conjoined twins start their new life after undergoing successful surgery to separate them at Human Children’s Hospital in Changsha on Wednesday. The two 6-week-old sisters, Zheng Qianyan and Zheng Wanyu, will be closely monitored as they recuperate. [Photo provided to China Daily]?

CHANGSHA - Doctors in central China's Hunan province on Wednesday successfully separated 43-day-old conjoined twin girls in a challenging operation.

The twin girls, born in late November, shared a liver and had their heart-sac connected. The two also suffered congenital heart disease, according to doctors in the Hunan Children's Hospital in Changsha, capital of the province.

The operation went well despite challenges. The girls are now being intensively monitored as they still have to make it through the critical seven days after the surgery, said Zhu Yimin, head of an expert panel on the operation.

Over 20 doctors worked on the twins' surgery, Zhu said.

The girls are in a stable condition but doctors are still on high alert as possible infections after the surgery could be fatal.

The twins are from the city of Yongzhou, about 320 km from Changsha.

Conjoined twins are quite rare, with the phenomenon's occurrence estimated to range from one in 50,000 births to one in 100,000 births. Most of them die before birth and only one in 200,000 is born alive.