As early as the sixth week of your pregnancy, your womb, which is in fact a large muscle, can contract regularly. These contractions (also called Braxton-Hicks contractions) are normally irregular and painless. Because they do not dilate the cervix, they are harmless for the pregnancy. They last 1 to 2 minutes.
Sometimes you get this kind of contractions only in the second half of your pregnancy, and sometimes you do not feel them at all.
Why do I have Braxton-Hicks contractions?
During pregnancy, the uterus regularly contracts to create better blood flow through the placenta and the baby. They are thought to also strengthen and prepare the uterine muscles for the delivery process.
How does a Braxton-Hicks contraction feel?
Braxton-Hicks contractions are generally not painful, but can feel uncomfortable. It feels like your belly and lower abdomen are hardening.
When will it be serious?
Braxton-Hicks contractions that increase in frequency and intensity at the end of pregnancy can be confused with real contractions. Hence the name 'false contractions'. Women are often unaware of the expansion of the cervix. This can only be measured by a midwife or doctor during a study.
What to do
If you have more than 4 contractions, painful or painless, at any time of pregnancy, or contractions that are less than 15 minutes apart, you must report this to your midwife. Answer the following questions:
While you wait for the midwife to call back or visit:
At some point, somewhere between the 35th and 40th week of pregnancy, the hard bellies change, causing them to soften and open the uterus. The contractions are now also called 'indwelling contractions'. Ultimately, this results in the actual birth. If the contractions lead to birth before the 37th week, then this is a premature delivery.
The real delivery
Contractions during the actual delivery are more painful and come with more regularity. The contractions will follow each other faster, and they will also become more intense.
From Cassandra-Harmon In Q&A