Braxton-Hicks contractions (named for the physician who first described them) begin very early in pregnancy and continue until labor begins, growing in frequency and strength as the pregnancy progresses. Some women feel them very early in the pregnancy, while others don't notice them until the last few months. They occur as a result of the uterus growing and are "practice" contractions to prepare the uterus for the work it will do in labor.
Braxton-Hicks contractions are usually felt as a generalized abdominal squeezing or tightening. They are perceived as a sensation of your uterus "balling up" in the front of your abdomen, and your tightening uterus can be felt when you place your hands on your abdomen. They come and go in an irregular pattern, and are often triggered by exercise or sexual activity. Braxton-Hicks contractions are usually painless, and will begin the process of cervical effacement and dilatation in the last weeks of pregnancy. If you change positions, walk, and drink fluids they will eventually go away; when you experience these contractions for a period of time, this is called "false labor". They can provide a good way to practice for labor if you relax your body and do slow paced breathing as you experience them.
On the other hand, true labor contractions are perceived as a sensation that starts low in your back and then radiates around to the front in the groin area, very much like menstrual cramps. For most women these contractions will not begin until 38 to 40 weeks gestation. They are often accompanied by other symptoms of labor, such as a discharge of bloody "show" or the water breaking. True labor contractions do become very regular in their pattern and get closer together (five minutes or less apart), last longer (60 seconds), and become more uncomfortable over time. Changing positions, walking, or drinking fluids does not make them go away. True labor contractions cause the progressive changes in the cervix (effacement and dilatation) that enable the baby to be born.
Braxton-Hicks contractions can be distinguished from preterm labor contractions (before 38 weeks gestation) by these symptoms:
If you experience any of these symptoms along with contractions, and are uncertain whether the contractions are Braxton-Hicks or preterm labor contractions, call your health care provider. A quick vaginal exam can let you know whether your contractions are something more than the normal Braxton-Hicks contractions of pregnancy.