Most women will start having very mild and short uterine contractions starting at about 32 weeks. These are called Braxton-Hicks contractions.
These contractions will appear a few times per day and last 5 to 30 seconds. They may only affect part of the uterus.
You might feel some vague chest discomfort or notice a change in breathing while you are having these contractions.
These contractions are a consequence of your uterus “practicing” how to contract and are very different from the “real contractions” that you will have in labor. If you notice them very frequently or if they become painful, do let your health care provider know right away.