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The Physiological Difference Between Braxton Hicks and Labor Contractions

There is one simple difference between Braxton Hicks and labor contractions: the end result.

Have a baby?  Those were labor contractions. No baby?  Braxton Hicks.

Ok, that’s not very helpful if you are trying to tell the two apart without a crystal ball on hand. But you can use a few tricks to tell Braxton Hicks from labor contractions. One of these tricks that most care providers recommend is tracking and timing contractions. Braxton Hicks usually keep an irregular pattern. Labor contractions have a consistent, regular pattern and closer together.

At a physiological level, there is a good reason why this rule of thumb works.

Let’s start with a visual:

difference betwen Braxton Hicks and labor contractions
Contraction patterns and characteristics change across pregnancy and into labor.

 

What are Braxton Hicks contractions?

Remember that contractions are totally normal throughout pregnancy. Often non-labor contractions, whether they are “warm-up contractions” (the body has to get ready!) or are caused by stress or dehydration, get classified the same way. The assigned name that you’ll hear thrown around – Braxton Hicks contraction – is simply the catch-all for any non-labor contractions during your pregnancy. For simplicity sake, like everyone else, we’re lumping them all together and calling them “Braxton Hicks”. 

 

Difference between Braxton Hicks and labor contractions

Braxton Hicks contraction = isolated muscle flex

There are big differences between Braxton Hicks and labor contractions at a physiological level.

Let’s start all the way down at the cellular level.

The uterine muscle (also known as the myometrium) is made up of individual muscle cells all working together… kind of. In the early days of pregnancy, these independent cells (called myocytes) contract and flex in isolation.  Sometimes they join their next door neighbor myocyte in the effort and sometimes they collaborate in small muscle clusters.

Contractions at this time are uncoordinated, isolated, and less frequent. Later in pregnancy, contraction frequency picks up but they are still uncoordinated across the uterus.  At a physiological level, these pesky Braxton Hicks contractions are like little muscle twitches, just sporadic moments of uterine muscle flexing.  Often they are felt in one spot or as intermittent tightening. Quite different from labor contractions…

 

Labor contraction = synchronized wave

During labor and delivery, contractions across the uterus sync up.  With these true labor-inducing contractions, the individual uterine muscle cells start to work together [1]. And they flex in synchrony like a wave across the whole uterus [2].

 

But contractions only earn the distinction of “labor contraction” when they cause the next critical component of baby eviction: cervical dilation.

Cervical dilation relies heavily on contractions. During labor, with more and more synchronous contractions, pressure within the uterus (called intrauterine pressure, IUP) increases. The increase in pressure starts working the baby down towards the exit. Pressure on the cervix – from the internal pressure building up from synchronized contractions and physical pressure from baby – causes the cervix to soften and open (also referred to as effacement and dilation) [3].  Pressure on the cervix also does a neat little trick of telling the brain to increase contractions (via oxytocin) and keep the everything ramping up to the climactic conclusion – a baby!

Intense coordinated contractions, an open cervix, a bit of help from mom’s pushing and baby arrives into the world with the placenta following close behind.

Simply put:  labor contractions = contractions that pop out a baby.

Easy, right?

 

Braxton Hicks contractions = sporadic uterine muscle activity.

They are a natural part of pregnancy.

 

Labor contractions = Synchronized uterine muscle activity.

They lead to cervical dilation and baby. Woohoo!

 

While we can’t help you get that crystal ball quite yet, we can offer a tool to help check in and keep an eye on those contraction patterns.  Bloomlife automates your contraction timing so you can see patterns in real-time and see how they change leading up to the big day.

Crystal ball coming soon.


P.S. Interesting tidbit:

The signs and symptoms of labor remain somewhat of a mystery to the medical and research world. As you may have guessed, contractions and other physiological markers are very promising targets for research. We, at Bloomlife, are proud to be at the forefront of this research. You can read more about how our mission and ongoing research projects leverage the Bloomlife technology and expertise to help solve the mysteries of labor to advance prevention and treatment of pregnancy complications, such as preterm birth.


REFERENCES:

1. Smith R, Imtiaz M, Banney D, Paul JW, Young RC. Why the heart is like an orchestra and the uterus is like a soccer crowd. Am J Obstet Gynecol. 2015;213: 181–185.

2.  Young RC. Synchronization of regional contractions of human labor; direct effects of region size and tissue excitability. J Biomech. 2015;48: 1614–1619.

3. Smith, R. Parturition. N. Engl. J. Med. 356, 271–283 (2007).

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Molly Dickens, PhD

About Molly

Molly has her PhD in Physiology and spent over a decade as an academic research scientist slightly obsessed with the colliding worlds of brain science, hormones, stress and the reproductive system. Nowadays she heads up Content and Community at Bloomlife and edits Preg U. Science is still her jam and she can't help but continue to dive into the research world to find interesting bits about pregnancy and parenting.

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