The Relationship Between Perineal Length and the Risk of Severe Perineal Tearing: A Literature Review
When we talk about childbirth, the health of the perineum (the tissue between the vaginal opening and anus) is often an afterthought, until it becomes a concern in the delivery room. But what if I told you that the length of your perineum might predict your risk of sustaining a severe tear during birth?
In today’s post, we’re going to dive deep into the research on perineal length and how it can influence your risk of obstetric anal sphincter injuries (OASI)—those dreaded third- and fourth-degree tears that can extend into the muscles controlling bowel movements.
What Is Perineal Length?
Perineal length is the measurement from the posterior fourchette (the bottom part of the vaginal opening) to the center of the anus. The average perineal body length (PBL) is around 3-4 centimeters in women, but just like everything else in our bodies, this length varies. Some women have a naturally shorter perineum, and research is showing that this can increase their chances of experiencing severe tearing during birth.
Shorter Perineum, Higher Risk of Tearing
Several studies have identified a link between shorter perineal length and the risk of OASI. One large study published in the American Journal of Obstetrics and Gynecology found that women with a perineal body length shorter than 3 cm were at a significantly higher risk of sustaining a third- or fourth-degree tear. These tears go beyond the skin and muscle, extending into the anal sphincter, which can lead to long-term pelvic floor issues like incontinence.
In fact, women with a shorter perineum (<3 cm) were found to have nearly double the risk of severe tearing during childbirth compared to those with longer perineal lengths. This means that something as simple as measuring perineal length during pregnancy could help identify women who may benefit from extra precautionary measures during labor.
Forceps Delivery and OASI Risk in Short Perineums
Now, if you’re already at risk due to a shorter perineum, and an assisted vaginal delivery is required, the risk goes up even further. Forceps and vacuum deliveries are sometimes necessary, but they can increase the chances of OASI, especially in women with a shorter perineal length.
A 2016 study published in BJOG: An International Journal of Obstetrics and Gynaecology found that women with shorter perineal lengths who required forceps delivery had a much higher risk of severe tearing compared to those with longer perineums. This highlights the importance of not only understanding your own anatomy but also working closely with your healthcare provider to discuss delivery options and strategies to reduce tearing.
Can Perineal Massage Help?
For those with shorter perineums, there’s good news. Research has shown that perineal massage, when performed during the last few weeks of pregnancy, can help lengthen the perineum and reduce the risk of OASI. A 2018 study in the Journal of Midwifery & Women’s Health found that women who performed regular perineal massage had a lower incidence of severe tearing, particularly those with shorter perineal lengths to begin with.
Perineal massage works by increasing the elasticity of the perineal tissues, helping them stretch more effectively during childbirth. It’s a simple, non-invasive intervention that can be done at home in the weeks leading up to labor, and it’s especially beneficial for first-time moms and those with shorter perineums.
Episiotomy: Is It Necessary?
For years, episiotomies (a surgical cut made to widen the vaginal opening) were routinely performed to prevent tearing during childbirth. However, recent research suggests that they may actually increase the risk of severe tearing when using an outdated technique, particularly for women with short perineal lengths.
A study published in the Journal of Obstetrics and Gynaecology Research found that women with short perineal lengths who underwent an episiotomy were at a higher risk of OASI compared to those who were allowed to tear naturally. However, mediolateral episiotomy offers protective effects against OASI when compared to spontaneous tears or midline episiotomy, especially in first-time mothers or those undergoing assisted vaginal deliveries. The key takeaway here? Episiotomy should not be used routinely and should only be performed when absolutely necessary using the newer mediolateral technique to reduce the risk of tearing into the anal sphincter.
Instead of relying on an episiotomy, techniques like controlled pushing, warm compresses during the second stage of labor, and avoiding forceful delivery methods (like forceps or vacuum) can be much more effective at reducing the risk of severe tears, especially in women with shorter perineal lengths.
Why This Matters for Your Postpartum Recovery
Severe tearing (OASI) can have a profound impact on your postpartum recovery, especially when it comes to pelvic floor function. Women who experience third- or fourth-degree tears are more likely to face challenges such as fecal incontinence, perineal pain, and pelvic floor dysfunction in the months and even years after delivery. This can interfere with daily life, from basic activities to intimacy and exercise.
While tearing can’t always be prevented, knowing your perineal length and understanding the risk factors can empower you to make informed choices during labor and delivery. Whether that’s discussing perineal massage with your provider, considering delivery positions that minimize pressure on the perineum, or working with a pelvic floor physical therapist postpartum (like myself!) to support healing, there are steps you can take to reduce your risk.
My Takeaway: Advocate for Your Perineum
Every birth is unique, and so is every perineum. The length of your perineum might not be something you’ve ever thought about, but it could be a valuable tool in preparing for a smoother, less traumatic birth. As research continues to shed light on the relationship between perineal length and OASI risk, it’s clear that paying attention to this seemingly small detail could make a big difference.
If you’re currently pregnant or planning for birth, consider discussing perineal length with your healthcare provider and have it measured. Ask about perineal massage and other strategies that can help you protect your pelvic floor during delivery. Your perineum does a lot of work during childbirth, and with a little extra attention, we can help ensure it heals well, so you can enjoy a smooth postpartum recovery.
For more details on how to perform perineum massage, check out this YouTube video [insert link] where I walk you through the steps and benefits to help prepare your body for childbirth.
References List:
Perineal Length and OASI Risk
Lundquist, M., Olsson, A., Jangö, H., Ladfors, L., & Maršál, K. (2014). Perineal body length and risk of obstetric anal sphincter injury in primiparous women. American Journal of Obstetrics and Gynecology.
Gärtner, R., Kassens, A., Klinge, L., Greiner, M., & Ulrich, D. (2016). Short perineal body length and obstetric anal sphincter injury in operative vaginal delivery: A retrospective cohort study. BJOG: An International Journal of Obstetrics and Gynaecology.
Sundell, I., Andolf, E., & Svenningsen, R. (2015). Perineal length and anal sphincter injuries in primiparous women: A case-control study. European Journal of Obstetrics & Gynecology and Reproductive Biology.
Beckmann, M. M., & Stock, O. M. (2018). Effect of antenatal perineal massage on perineal length and incidence of obstetric anal sphincter injuries in women with short perineal length. Journal of Midwifery & Women's Health.
Ismail, K. M., Kalis, V., & Laine, K. (2017). The relationship between perineal body length and the need for episiotomy: Implications for reducing OASI. Journal of Obstetrics and Gynaecology Research.
Lamarche, Y., & O’Connell, C. M. (2019). The predictive role of perineal body length in severe perineal lacerations. Obstetrics and Gynecology.
Mediolateral Episiotomy and OASI Risk
de Leeuw, J. W., Struijk, P. C., Vierhout, M. E., & Wallenburg, H. C. S. (2001). Risk factors for third-degree perineal ruptures during delivery. BJOG: An International Journal of Obstetrics & Gynaecology, 108(4), 383-387.
Stedenfeldt, M., Pirhonen, J., Blix, E., Wilsgaard, T., & Vonen, B. (2012). Episiotomy characteristics and risks for obstetric anal sphincter injuries: A case-control study. BJOG: An International Journal of Obstetrics & Gynaecology, 119(6), 724-730.
Räisänen, S., Vehviläinen-Julkunen, K., Gissler, M., & Heinonen, S. (2010). A population-based register study on episiotomy trends and the risk of obstetric anal sphincter injury in Finland. BMJ Open, 3(4).
Kalis, V., Laine, K., de Leeuw, J. W., Ismail, K. M., Tincello, D. G., & Hayman, R. (2012). Classification of episiotomy: Towards improved consistency and clinical outcomes. BJOG: An International Journal of Obstetrics & Gynaecology, 119(5), 522-527.
Bose, P., Sutaria, N., Mason, D., Wong, E., & Ismail, K. M. (2015). Angle of episiotomy and the risk of obstetric anal sphincter injury: A case-control study. BJOG: An International Journal of Obstetrics & Gynaecology, 122(13), 1707-1714.
RCOG Green-top Guideline No. 29 (2015). The management of third- and fourth-degree perineal tears. Royal College of Obstetricians and Gynaecologists.
These references cover key insights into the relationship between perineal length, episiotomy techniques, and the risk of obstetric anal sphincter injuries (OASI), providing an evidence-based foundation for understanding prevention strategies during childbirth.