Round ligament pain in pregnancy is very common. It typically does not start until the second trimester and is usually seen when you make a sudden or jerky movement, frequently when moving side to side.
The round ligament actually anchors your uterus. As the uterus expands, the round ligament gets stretched like a rubber band. When you move in certain ways or sudden twist or turn, these ligaments can make a "snapping" movement, causing pain.
Typically once the sudden pain is gone, you will not be in pain. Though if you have a lingering ache, you can use warm compresses or heat to help ease the ache.
You can also use a slow side stretch to help ease the pain.
Typically this pain doesn't start until closer to 20 weeks into your pregnancy. But it can happen all of a sudden with no warning and that can be really frightening. Don't hesitate to talk to your doctor or midwife about this pain and how to cope with it in pregnancy.