A giant panda has given birth to twin cubs at Toronto Zoo.

They are the first cubs to be born in Canada since the zoo was loaned two pandas by China in 2014. Er Shun was impregnated with sperm collected from Da Mao.

The gestation period for a giant panda is anywhere from 87-186 days from the date of insemination. It is difficult to predict when they will give birth since giant pandas exhibit what is called "delayed implantation."

A study by Hemin Zhang and colleagues published by the journal Reproduction in 2009 describes the phenomenon thus: "...the embryo floats in the womb and arrests development until it attaches to the uterus months later."