The zoo expects the babies will be born in the next three to four weeks.
They are "cautiously hopeful" and the coming weeks are critical.
Er Shun and Da Mao arrived from China in 2013.
Also on HuffPost
Pandas at Edinburgh Zoo
MORE:Er Shun Da Maoer shun panda cubser shun pregnanter shun torontoer shun toronto zooinspiringLivingliving videopanda pregnant torontopanda twin cubspanda twins torontoToronto Zootoronto zoo giant panda pregnanttoronto zoo giant pandastoronto zoo panda pregnanttoronto zoo pandasvideoSuggest a correction