ATLANTA: The mother of the only giant panda twins in the United States may soon deliver a second set of twins, Zoo Atlanta said on Tuesday, capping off an eventful month for lovers of the fluffy black and white bears across the globe. Three years ago, mother bear Lun Lun gave birth to female cubs Mei Lun and Mei Huan, who are still at the Georgia zoo but could be returned this fall to China, which owns them, zoo spokeswoman Rachel Davis said. An ultrasound on Monday confirmed that Lun Lun, who turns 19 years old on Thursday, is once again pregnant with twins, the zoo said. Delivery of the new twins could be in the next few weeks, Davis said, calling the pregnancy a surprise. Panda pregnancies, famously rare in captivity and outside of China, are notoriously hard to establish or predict. The rarest member of the bear family with roughly 1,864 in the wild, pandas live mainly in bamboo forests high in the mountains of western China, where they subsist almost entirely on bamboo leaves. News of the pregnancy comes as twin panda cubs born at a zoo in Vienna, Austria, turned 16 days old on Tuesday and were said to be fit and healthy – and very cute. In China, twin panda cubs, a male and a female, were born at a breeding research base in southwest Sichuan province on Aug. 9, state broadcaster CCTV reported. In Atlanta, Lun Lun was impregnated by artificial insemination on March 28, the zoo said. There is no guarantee the birth will be successful since a condition known as fetal resorption, or Vanishing Twin Syndrome, in which a fetus dies before it is born, is “not uncommon” in pandas, the zoo said. If Lun Lun’s second set of twins survive, they will be her sixth and seventh cubs, Davis said. Newborn panda cubs are very vulnerable, being about the size of a stick of butter, according to the World Wildlife Fund. They can grow to up to 330 pounds (149.69 kg) as an adult. While about half of all panda deliveries are twins, mothers in the wild typically only care for one cub, Zoo Atlanta said. “Advances in animal care and veterinary care in zoos have resulted in successful rearing of twins both in the zoological population in China and in zoos outside China,” Zoo Atlanta said in a statement. While the zoo will be closely watching Lun Lun, the rest of the world can also keep an eye on her and perhaps watch her give birth over a live camera streamed at www.zooatlanta.org.