BERLIN (AP) — Berlin Zoo announced Friday that longtime resident giant panda Meng Meng has given birth to twins — for a second time.

The cubs were born on Thursday and are doing well, the zoo said in a statement. They were born only 11 days after ultrasound scans showed that Meng Meng, 11, was pregnant. Their sex has not yet been determined “with certainty.”

“Now it’s time to keep your fingers crossed for the critical first few days,” the zoo said. The cubs are tiny, weighing just 169 grams and 136 grams (about 6 ounces and 4.8 ounces) respectively, and are about 14 centimeters (5.5 inches) long.

As with other large bears, giant pandas are born deaf, blind and pink. Their black-and-white panda markings only develop later.

Meng Meng and male panda Jiao Qing arrived in Berlin in 2017. In August 2019, Meng Meng gave birth to Pit and Paule, also known by the Chinese names Meng Xiang and Meng Yuan, the first giant pandas born in Germany.

The twins were a star attraction in Berlin, but they were flown to China in December — a trip that was contractually agreed from the start but delayed by the COVID-19 pandemic. China gifted friendly nations with its unofficial mascot for decades as part of a “panda diplomacy″ policy. The country now loans pandas to zoos on commercial terms.

Giant pandas have difficulty breeding and births are particularly welcomed. There are about 1,800 pandas living in the wild in China and a few hundred in captivity worldwide.

Meng Meng was artificially inseminated in March. The zoo noted that female pandas are only fertile for about 72 hours per year.