Putting a Pregnancy on Hold

Some animals can 'pause' their pregnancy for more favourable conditions.

So last week we touched on kangaroos, koalas and other marsupials having three vaginas. This time, we’re going to talk about embryonic diapause.

Embryonic diapause. The term alone sounds like some crazy science fiction. But let me assure you, it's far from that. In fact, it's a fascinating reproductive strategy used by a number of different animals to pause their pregnancy. Animals that use this strategy include more than 130 species of mammals, as well as some fish and insects.

Some animals are lucky enough to take a break from their pregnancy. Photo by Alexas_Fotos on Unsplash

First things first, let's break it down. Embryonic diapause is a nifty little trick that some animals have up their sleeves. And they use it for two reasons.

The first are when conditions are less than ideal for reproduction. Unideal conditions can include the lack of food and resources, waiting for older siblings to be weaned, or stressful environments such as an abundance of predators. So essentially, any conditions that reduce the chances of the newborn and mother surviving.

The lack of food can trigger animals like wombats to pause their pregnancy. Photo by Nico Smit on Unsplash

The second is, it acts as a backup pregnancy in case something happens to their newborn. If for some reason, the newborn does not survive, the pregnant mother can immediately resume her pregnancy and pop out another newborn to maximise her reproductive success.

Whatever the case may be, the mother can decide if it's not the right time to bring a newborn into the world. So, she can pull the ultimate parental move and hit the pause button. Pretty cool huh?

Now, you might be thinking, "How in the world can you hit pause on a pregnancy?” Well, the mother delays the implantation of their embryos in the uterus. Only once the embryo is in the mother’s uterus, can it be nourished to develop into a baby. So, by preventing implantation, she can effectively put the development of the embryo on hold until a better time comes around.

And in the case of already having a newborn at foot, the stress response produced by the lactation triggers her to pause her pregnancy. Once the mother is no longer lactating (from either having a fully developed young or her newborn not surviving), will her pregnancy be triggered to resume. And before you know it, she’ll pop out another baby.

A joey suckling at their mother’s teat will also trigger embryonic diapause. Photo by Ethan Brooke on Unsplash

So essentially, embryonic diapause is nature's way of saying, "Hold up, let's think this through." It's like the ultimate timeout, giving animals the chance to reassess their options and make sure they're bringing their offspring into the best possible world. If only we had that superpower to pause being pregnant whenever we wanted.