In their defense, it has to get pretty cramped in there by the third trimester.
Twins are known for fighting and bickering, but a fascinating new video showing a couple of soon-to-be born siblings shows just how early that pattern begins!
The footage, from inside the womb, demonstrates what really goes on in utero, and it's unharmonious, with the kiddos exchanging kicks in a bid for extra legroom.
In all seriousness, this was observed as part of a serious medical study:
A high-tech monitor known as the "cinematic MRI" allows doctors to see, in better detail, when twins vie for space in utero and the potential consequences of that.
Dr. Marisa Taylor-Clarke of Imperial College's Robert Steiner MR Unit in London said this has an important application on a diagnostic level for twins.
Doctors use it to diagnose how fetuses are affected by twin-to-twin transfusion syndrome (TTTS) - a condition in which one identical twin siphons blood away from the other.
"A lot of the so-called videos in the womb are very processed, so they do a lot of reconstructing and computer work afterwards," Taylor-Clarke told Reuters.
"These are raw images that are acquired immediately."
This condition deprives the "donor" of nutrients and can put too much pressure on the heart of the one receiving the lion's share, according to the Twin To Twin Transfusion Syndrome Foundation.
It can occur at any time during pregnancy. While a regular ultrasound may be able to detect TTTS, it does not reveal its impact; researchers hope to change that.