What is delayed implantation in nine-banded armadillos?

In the nine-banded armadillo (Dasypus novemcinctus), delayed implantation refers to a variable period of up to several months that occurs between the fertilization of the egg and its subsequent implantation into the wall of the uterus.1

While the species has a gestation period of four months, this duration does not include the delay period. This reproductive strategy allows the armadillo to time the birth of its young, which are produced through polyembryony—a process where a single fertilized egg develops into a set of four identical quadruplets.21