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.