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Membrane Sweeping: The Research and the Risks

What is membrane sweeping, what does the research say about it, and what are the risks? That’ s exactly what this blog post covers.

pregnant woman talking to a doctor

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Whether you’re curious about different forms of induction, you’re trying to avoid as many interventions as possible, or you want to know what to expect at prenatal appointments, you might have heard about membrane sweeping. 

Membrane sweeping is a routine procedure at many OBGYN clinics and has some benefits but it isn’t without risk.

Let’s look at what membrane sweeping is, why and when it’s done, and what the research says about it. Plus, we’ll go over the risks and a few other factors to consider when deciding whether or not to get a membrane sweep.

Membrane Sweeping: What, When, and Why

The “membrane” referred to in membrane sweeping is the amniotic sac, the bag of tissue that forms inside your uterus to hold the amniotic fluid and your baby.

A membrane sweep separates this bag from your uterus.

A care provider usually performs the procedure during a cervical check. Your cervix has to be somewhat open (or dilated) to perform a membrane sweep.

To do a membrane sweep, which is sometimes called a “stretch and sweep,” your care provider will insert a finger or two into your cervix and slide their fingers around the base of your uterus, creating a small gap between it and the amniotic sac.

Separating the uterus and amniotic sac can stimulate the cervix and encourage the release of hormones that trigger labor. It is a form of induction.

Membrane sweeping (sometimes called membrane stripping) is often done to encourage labor to start before medical means of induction are recommended. It may also be used as a precursor to other forms of induction to help those methods be more effective.

Membrane sweeping is routine at most clinics, done for all women as part of a cervical check. Some care providers begin to perform membrane sweeps as early as 36 weeks of pregnancy.

What Does the Research Say About Membrane Sweeping?

A lot of research has been done on the topic of membrane sweeping. Overall, most studies agree on a few things.

First, membrane sweeping often reduces the need for medical induction later on. Many researchers have found that women who get one or more membrane sweeps go into labor before doctors feel they need to recommend another form of induction, such as administering Pitocin.

Second, for those women for whom the sweep is effective, membrane sweeping can encourage labor to start within a week of the procedure. In other words, membrane sweeping may shorten your pregnancy by a few days.

Third, membrane sweeps can improve a woman’s Bishop Score within 48 hours. A Bishop Score is a way to combine all five characteristics that a cervical check looks for: position, softness, effacement, dilation, and baby’s station.

Finally, research has shown that membrane sweeping does NOT reduce the risk of c-section, decrease the likelihood of instrumental vaginal delivery, or make any difference in the rates of illness or death for mother or baby.

Risks and Downsides of Getting a Membrane Sweep

Membrane sweeps in and of themselves are generally a fairly safe procedure. That said, there are risks and other downsides.

The biggest potential risk of membrane sweeping is the possibility of triggering premature labor.

Many healthcare organizations agree that discussing a membrane sweep with pregnant women should happen at or after 39 weeks of pregnancy. Unfortunately, that standard is not always put into practice.

Many care providers begin routine membrane sweeping when they begin routine cervical checks – around 36 weeks.

Membrane sweeping does not always trigger labor. But if it were to begin labor at 36 or 37 weeks of pregnancy, it is much more likely that that baby will not be fully developed or ready for life outside the womb. (Full term is 39 weeks.)

The other main risk of membrane sweeping is the possibility that your care provider will accidentally break your amniotic sac (i.e. “break your water”) while performing the sweep. If a woman is full term, the break will likely encourage labor to begin and things will proceed normally.

If a woman is not full term or if labor does not begin within a day or two, she is at risk of developing a uterine infection. Because of this, most care providers will medically induce a woman if her baby is not born within 24-48 hours of her water breaking.

Another downside of getting a membrane sweep is that it can be painful, both during and after a sweep. The cervix is a highly sensitive area so it can be quite uncomfortable when it is touched.

After a membrane sweep, some women experience bleeding and cramping. While that is common and usually not dangerous, it isn’t pleasant.

Have a Conversation BEFORE Cervical Checks Begin

It’s also important to know that membrane sweeping is sometimes done without a woman’s knowledge or consent.

Some providers consider a membrane sweep to be a normal part of a cervical check so they will not ask for consent before doing the sweep. That is wrong. You have the right to decline a membrane sweep (and cervical checks altogether if you want!).

To avoid this, have a clear conversation with your provider before 36 weeks. Communicate that you do not want a membrane sweep done without your consent.

Two Last Things to Consider

Now you know what the research says and what risks membrane sweeping poses. I want to point out two final things that are important to consider before making a decision about getting a membrane sweep.

Data Misrepresented and Delayed Inductions

First, it’s important to recognize that not all studies are created equal. The Cochrane Library study that I reference in this blog post is a meta-analysis, meaning a study of lots of previous studies.

The meta-analysis was well done. But it clearly states that in most of the studies it looked at, “evidence certainty…was found to be generally low, mainly due to study design, inconsistency and imprecision.” In other words, it wasn’t very high quality research in the first place.

One of the main issues with the studies this analysis examined was that none of them used  “masking.”

That means the doctors knew which women were being studied to see what benefits membrane sweeping might have. And that means the doctors may have been biased in providing better care for the women who received a sweep.

The biggest implication here is that doctors may have delayed medical means of induction  (e.g. giving Pitocin) longer than they normally would have for the women they had done a sweep on, in hopes that they would go into labor spontaneously and thus show that membrane sweeping was effective. 

So, while “studies show” that labor starts on its own more often with a membrane sweep, we may not be able to generalize that information because doctors in the real world don’t usually wait as long before medically inducing labor.

Was It the Sweep or Was Your Body Already Ready?

Second, researchers did find that membrane sweeping improved women’s Bishop Scores within 48 hours. But we need to remember that Bishop Scores are not perfect predictors.

Care providers use the Bishop Score to assess how likely it is for an induction to be successful. But, as I explain in Cervical Checks During Pregnancy: It’s Up to You, a Bishop Score can NOT tell you anything except for the condition of your cervix at the time of the check.

That information just allows for a more educated guess.

And that means it cannot tell you how soon labor will begin. 

The other issue with using Bishop Score as an indicator of success is that progress may not be due to the membrane sweep at all.

Membrane sweeping is more effective on or after a woman’s due date. But at that point, it’s likely that her body is already gearing up for labor. So membrane sweeping might be less a way to get labor started than it is a way to speed up the first stages of labor once it’s already begun.

Conclusion: Should You Get a Membrane Sweep?

So should you get a membrane sweep?

All things considered, membrane sweeping isn’t incredibly dangerous. The biggest risks are the possibilities of triggering premature labor and accidental breaking of the amniotic sac. But both are relatively unlikely.

In addition to risks, membrane sweeping can be uncomfortable and can lead to bleeding and cramping afterwards.

And finally, even though the research says membrane sweeps are effective, it’s possible that the research was biased. Plus, the condition of your cervix can’t guarantee that labor will begin anytime soon.

Personally, I recommend avoiding all unnecessary intervention, including membrane sweeping, because the possible benefits are far outweighed by the risks.

If you really want to not be pregnant anymore and you are past 39 weeks, a membrane sweep might be a good option. But remember, the difference is likely days, not weeks. And if a membrane sweep is effective, it’s likely that your body was going to begin labor soon anyways.

Remember, your body was designed for this. Your body grew your baby, your body can birth your baby. And it will do it when it and your baby are ready. Trust that.

Until next time,

Allison

READ MORE:

The Cascade of Interventions [Explained]

Medications During Labor: Is It Worth the Risk?

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