Par·a·dox - a statement that is seemingly contradictory or opposed to common sense and yet is perhaps true. For example, petite women can deliver large babies vaginally without complication whereas smaller babies can get stuck navigating into the world through a woman with a more spacious pelvis. I refer to this as the pelvic paradox.
Since many women have hopes for a labor and delivery experience that is as smooth as possible, I want to address the causes of the Pelvic Paradox. We’ll discuss how you can proactively influence your body’s physiology to prepare for your optimal childbirth.
What causes the Pelvic Paradox?
There are several contributing factors to the pelvic paradox including musculoskeletal function. Musculoskeletal function is broken down into two components:
- Anatomy: refers to structures of the body
- Physiology: refers to how those structures function.
Structurally the bony pelvis is not a single solid bone. Rather, it consists of several bones connected by ligaments and other soft tissue. An unborn baby’s head is also not a solid bone, but instead several bones that are connected but not yet fused together. Therefore, we can actually influence both structure and function.
During childbirth, a well functioning pelvis should be able to expand and contract to accommodate or even facilitate the baby’s movements down and out even if the baby is larger than the mothers pelvic outlet. Similarly during a head-first vaginal delivery, the unfused skull of the baby can mold from a round shape with a larger diameter into an oblong shape with a smaller diameter and pass through a smaller pelvis smoothly and without complication.
How can you influence musculoskeletal function?
Maximizing pelvic physiology during the final stages of pregnancy can help ensure that during labor the pelvis will have the fluid motion to accommodate the baby’s movements as it makes its way down; rather than resisting. Chiropractors are experts in musculoskeletal structure and function. In my office, we combine clinical massage to release excess tension in restricted soft tissue like muscles and tendons and chiropractic adjustments to restore motion to restricted joints; especially in the spine and pelvis. One of the most commonly known methods that chiropractors use with expecting mothers for this purpose is called the Webster Technique which involves specific adjustments to address pelvic subluxation and ligamentous tension.
Can you measure musculoskeletal function?
Towards the end of pregnancy, obstetricians may measure pelvic dimensions to help determine whether a woman can give birth vaginally or will require a cesarean section. This is called pelvimetry and is done by clinical examination, or with imaging. However, pelvimetry primarily tells about structure, not function. A picture of the maternal pelvis and fetal head shows their size in a snapshot of time, but doesn't reveal much about function.
In fact, a research paper by the American Academy of Family Physicians states “Current practice is to allow all women a trial of labor regardless of pelvimetry results. This makes the routine performance and recording of clinical pelvimetry a waste of time, a potential liability, and an unnecessary discomfort for patients.” When it comes to measuring the size of a baby to determine whether or not to schedule a cesarean section or induce early because of large baby size, the AAFP found that “Elective cesarean section is seldom a suitable alternative (to vaginal delivery), and elective induction of labor appears to increase rather than decrease the cesarean section rate.” The study much of these findings come from is called A Retrospective Review of Performance and Utility of Routine Clinical Pelvimetry.
More recently, the ARRIVE trial came up with different conclusions regarding induction and cesarean rates. As you can see, these topics are still hotly debated and more research is always in the works, however, it’s vital to understand how to interpret these studies in a detailed and nuanced way because not all medical studies are created equal. For a detailed discussion on the ARRIVE trial and some of my commentary, listen to this episode of my Informed Pregnancy podcast with obstetrician and maternal fetal medicine specialist Dr. Emiliano Chavira.
Similarly, practitioners use ultrasound imaging to estimate the weight of an unborn baby during prenatal visits. While there is no fetal scale, ultrasound machines use a series of formulas and calculations to come up with an estimated fetal weight. Despite modern technology, ultrasound weight estimates still have a significant margin of error of plus or minus one or more pounds. As a result of these inaccuracies, concerns about delivery of a ‘large’ baby are often raised and factored into birth options, with babies who come out average size or smaller.
What you can do to set yourself up for a smooth delivery
Expectant parents and providers want to do all that they can to ensure the safest delivery of a healthy baby. While no means of delivery is free of risk, most deliveries occur without significant complication. I encourage every expecting parent to become informed, and thereby, empowered. Choose a practitioner who you trust to help you make informed choices, who you trust to support those choices, and who you trust to provide you with the best environment for a safe and supported delivery not based on fear.
Dr. Elliot Berlin is an award winning chiropractor focusing on pregnancy and postpartum care. He lives in Los Angeles with his wife and four children.