Braxton Hicks contractions are a painless but sometimes uncomfortable tightening of the uterus. The contractions may be mild enough to go unnoticed or may be strong enough to make the woman stop what she is doing.

Braxton Hicks contractions might be considered "warm-up exercises" for the uterus during pregnancy. They can begin as early as the 20th week and increase through the 40th week (9th month) of pregnancy.

It is often hard to tell the difference between true labor and Braxton Hicks contractions. Braxton Hicks contractions:

• Tend to be irregular and vary in strength and do not become more regular or stronger.
• Are more noticeable when the woman is resting.
• Usually disappear with exercise (true labor pains may continue or increase if the woman walks around).
• Occur less than 4 times per hour.

True labor pains tend to last longer, become stronger, and occur closer together than Braxton Hicks contractions.