(CBS New) What really goes on when twins share a womb? If this video is any indication, it could be a similar to what happens once they’re young children — they fight.

The amazing images of twins in utero come from a study aimed at using MRI machines to diagnose a potentially deadly condition called twin-to-twin transfusion syndrome, Reuters reports.

The rare condition occurs only in identical twins, when blood from one twin moves into the other. That can significantly reduce the supply in the twin that loses the blood, causing him or her to be born smaller than their sibling, and with paleness, anemia and dehydration. The twin that receives the blood may be born larger than the other twin with increased blood pressure that may lead to heart failure.

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