Please check this, but I think this occurs in the kangaroo. The female becomes pregnant soon after giving birth, but the foetus is pretty much in stasis until the previous joey has left the pouch. Because the kangaroo gives birth at a relatively early stage of foetal development it is vital that the previous sibling has been weaned, because if the newborn can't attach itself to a teat very soon after birth it will die.
On a more mundane level, doesn't this describe what happens to a lot of plant seeds? i.e. until they are in the soil, with an adequate supply of water around them and until the weather has warmed up they sit dormant over the winter.