A few days ago, I was woke up to excruciating pain on my calf I had to scream: leg cramps! Although this is the first time I have experienced this, apparently, this is common during pregnancy, particularly during the last trimester. No one really knows why, but a lot of speculate these factors may contribute:

• Insufficient blood circulation, particularly to the legs
• Increased pressure on leg muscles due to the extra weight of pregnancy, leading to muscle fatigue
• Increased pressure exerted on the nerves and blood vessels leading to the legs

Here are two more references about leg cramps during pregnancy, tips on how prevent them, and what to do when you get them:

Leg Cramps During Pregnancy from BabyCentre

Leg Cramps from March of Dimes