Their anatomy was modeled by 3-D printing technology. The model was used to guide surgeons in the operating room. YIN LIQIN/CHINA DAILY

The girls were born on March 17 at a hospital in Ganzhou, Jiangxi province. Their conjoined condition was discovered only after they were delivered. Earlier prenatal checks showed only that they were twins.

The twins were soon taken to Fudan University's children's hospital, which has experience in separating conjoined babies. Since 2000, the hospital has handled separations of four symmetrical conjoined twins and two asymmetric twins.

Doctors said the ideal time for such a surgery is when the twins are three months old and with a weight of about 10 kg, enough for them to endure the surgery and recover.

Doctors also said it might take three days for the girls to get out of danger.

"We have given special attention to some possible complications, such as cerebrospinal fluid leak, which may lead to purulent meningitis and produce life risk," Zheng said.

A charity group donated 200,000 yuan ($32,200) to help pay for the procedure.

The hospital said conjoined twins are rare. Most are connected at the chest and abdomen. Only 18 percent are connected at the hip.

Contact the writer at wanghongyi@chinadaily.com.cn