A pair of premature twin boys discharged from a hospital in Chengdu, Sichuan province 20 days ago is gaining weight by more than 10 grams with each passing day, their parents said.

The twins were born on Sept 7 in Chengdu, Southwest China’s Sichuan province after their mother, who had resorted to in vitro fertilization, was pregnant for about six months.

The premature babies were very fragile. Their skin was as delicate as jelly and they could not breathe by themselves, according to Han Yanqing, a doctor with the neonatology department of Sichuan Women’s and Children’s Hospital.

After more than 70 days of treatment in the hospital, the babies left with their weight gaining from 980 and 1,080 grams at birth to 1,910 and 2,004 grams.

The babies have been well since they left the hospital for home, their parents said.