Anatomy, Function, and Physical Challenges
"I thought this was something that only happened to old people!" said Jan at her first visit to the office, three years after the birth of her twins.
Across cultures, continents, and generations, the birth of a newborn is a human moment that elevates us and provides our single clearest glimpse into the divine. What other experience throughout the human life cycle so universally suspends our cynicism and rekindles the possibilities of wonder and miracle? Childbirth is a timeless drama centered on the strength and determination of a heroine, supported by a cast of secondary players. Building its intensity with wailing, screaming, and puffing, it climaxes with a cry, collective awe, and lives forever changed. Labor is truly our most primal and natural act upon life’s stage.
On a less majestic plane, labor and delivery for our species represent a monumental physical strain. Whereas most physical degeneration in our bodies accumulates gradually across the years and decades of adulthood, during childbirth, we witness immediate and often irreversible injury occurring right before our eyes. At no other time would doctors and family members passively observe physical injury to a loved one without intervening—in a hospital room, no less! The blinding intensity of the labor drama, and our overwhelming fixation on the safe journey of the fetus, allow little opportunity for other concerns—even those concerning potential long-term problems for Mom.
“Just give us a healthy baby,” the young and the restless pray, “and we’ll deal with all the rest later on.”
A mother’s fate is often sealed in different ways. From that moment in time, for significant proportions of childbearing women, the die has been cast; they are destined to suffer urinary incontinence, anal incontinence, and pelvic-organ prolapse later in life. Through stretching, tearing, detachment, and compression, childbirth remains the major risk factor for these pelvic disorders. Within months or years, some of these women will be quizzing their peers and scanning the Internet, researching the various causes and latest treatments. Years later, greater numbers will stream into a doctor’s office in need of medication, a device, or surgery, expressing amazement that so many of their female friends seem to be suffering the same symptoms. WHY ALL THE STRUGGLE? Why have humans, for all our innocent efforts to procreate, been dealt such a complicated hand in the labor room?
Pelvic Floor Anatomy: A Response to Evolutionary Adaptations
Let’s consider, from the standpoint of obstetrics and gynecology, the impact of the past several million years of evolution on the human race. It’s been a mixed blessing, to say the least.
First, to accommodate an enlarging brain, the size of our cranium gradually increased well out of proportion to the rest of our body. While this change immensely improved the quality of cocktail conversations and university lectures, it wreaked havoc on the act of childbirth, leaving us with an extraordinarily large fetal head in comparison with the usual maternal pelvis. Look at polar-bear mothers: weighing over five hundred pounds, they deliver babies with heads smaller than humans’. In human obstetrics, there is very little room to spare!
Problem number two: we stood upright. While this earned us the ability to walk along the beach holding hands, and dramatically improved the aesthetics of ballroom dancing, we were unfortunately left with a pelvis much narrower from front to back, and a bit wider from side to side, in comparison to our knuckle-walking ancestors. This standing bipedal posture also shifted the opening of our bony pelvis directly underneath all of the weighty contents of the abdomen and pelvis. All of our organs were stacked right over a wide-open space, so the pelvis needed to devise enough strength and support to resist the forces of gravity pushing the bladder, uterus, vagina, and bowel downward through this bony pelvic opening. The vagina, in particular, was faced with the seemingly impossible task of supporting the weight of the uterus, bladder, rectum, and bowels all its life, then allowing a full-term baby to pass through—and afterward resuming function as a sexual organ while providing enough strength within its walls to continue holding back the bladder and rectum.
To make this new anatomy all the more challenging, the disproportion between baby and pelvis increased further as improving nutrition resulted in larger offspring over the centuries. For women who have multiple vaginal births, any supports covering this bony opening are stretched wider and wider with the delivery of each newborn.
The Evolution of Our Pelvic Floor Anatomy
What would happen over the millennia as a result of the remarkable physical stresses involved in childbirth? For every evolutionary challenge, the human body always seemed to devise a clever adaptation. But was this evolutionary mismatch, and the stress of human childbirth, too much of a challenge for the female body to surmount? No chance! On the contrary, the human species devised a remarkably clever solution: the pelvic floor.
The first priority of the pelvic floor would have to be providing support for the various organs lying above, including the uterus, bladder, and bowel. On the other hand, the floor couldn’t be a solid surface: through it, a few key hollow structures must pass, including the urethra, vagina, and rectum. While providing strength, the pelvic floor would need to allow these structures to function properly, keeping them closed most of the time but allowing them to open when needed.
A seemingly impossible compromise between competing demands: strong enough to withstand the constant pressure of internal organs, supportive enough to allow the vaginal, rectal, and urinary tubes to maintain control over bodily wastes, and flexible enough to allow a full-term baby to pass through. Quite an engineering challenge!
Muscles flexing, nerves firing, and bodily wastes being held at bay only inches from the outside world: could you have guessed that so much drama was taking place in this hidden area of your body?
Introducing your pelvic floor. It consists of several layers of muscular support stretching like a hammock across your pelvic opening. Intertwined within these layers are broad, overlapping muscles and connective tissue that surround your organs and secure them to your pelvic bones and spine. Muscles flexing, nerves firing, and bodily wastes being held at bay only inches from the outside world: could you have guessed that so much drama was taking place in this hidden area of your body? Let’s draw a map of your pelvic anatomy in the most practical terms, for those of you trying to understand your own bulging, dropping, or leaking, and for those looking ahead to childbirth. Aim your microscope at the basic components of the pelvic floor, so we can explore the physical act of childbirth from a new point of view.
The Perineum
The illustration here shows the perineum, the bridge of tissue between the opening of the vagina and the anus. It’s actually the connection point for several muscles that form the opening of the vulva and vagina. The perineum is a relatively easy anatomic structure to orient yourself to, because it’s external and visible, and also because it is the tissue intentionally cut during an episiotomy. So, let’s start our map of the pelvis right at the perineum, and use it as our first landmark of your pelvic floor.
Finding the perineum on your own body is easy. Looking in the mirror, identify your anal and vaginal openings; in between, you’ll see the span of tissue that is the perineum. It can vary in size from the width of a finger to several inches. In its normal prechildbirth form, the perineum joins several muscles (bulbocavernosus and transverse perineal) that form a solid muscular rim around the vaginal opening.
Now take a look at the anatomy surrounding your perineum. Above and to the sides, you’ll see the outer lips of the vagina, their outer surface covered with hair. When these labia majora are separated, you’ll see the labia minora, which look like thinner, hairless folds. At their top margin, they come together in the middle, near the clitoris. At their lowest point, they meet in the middle to form the fourchette, a sensitive area that can be a source of vaginal irritation. Beneath the perineum is the anal opening, surrounded by the anal sphincter muscles.
Finally, above the perineum and the vaginal opening, orient yourself to the urethra. Notice how the urethra sits right above the vagina. In later posts, we'll cover the importance of this close relationship and how changes to the area during childbirth can lead to problems.
The Levator Muscles
Let’s move to a deeper layer of the pelvis to reach perhaps the most important body parts when it comes to the physical effects of pregnancy and childbirth.
The levator muscles are the true foundation of your pelvic floor. Each day, whether you’re running, coughing, lifting, or just taking it easy, they’re the bedrock that provides your insurance policy against the constant downward force of the pelvic and abdominal organs.
You’ll never see or touch the levators, and they won’t affect the way you look in a swimsuit. But make no mistake—the health and conditioning of your levator muscles can strongly affect the way you feel and function.
A Shelf - Remember the wide, vulnerable opening right at the bottom of your bony pelvis—that problematic product of evolution? Like a shelf, several of the levator muscles form a sturdy barrier covering most of this pelvic opening and supporting the uterus, vagina, bladder, and other pelvic organs. When it’s functioning properly during a strong cough or sneeze, these organs and their supports bounce against the muscular floor like a trampoline, rather than bulging through the open space toward the outside of the body. The levator shelf provides your critical first-line pelvic-floor support and best protection against prolapse and other types of pelvic-floor dysfunction. Like any quality trampoline, the levator shelf can remain strong and resilient—bounce after bounce, year after year—unless it’s overly stressed, stretched, or abused.
A Sling - Other parts of the levator muscles function like slings, wrapping around the anal and urethral sphincters and keeping them tight when you’re not yet ready to void. These sling muscles play a major role in keeping you continent of urine, gas, and stool. The pubococcygeus and puborectalis are two of the most vital, encircling the rectum, urethra, and vagina. When you cough, bend, or swing a five-iron on the golf course, these muscles tighten almost instantaneously, contributing a burst of pressure at each sphincter to hold back the various waste products inside your body. Confused? Actually, you can locate your levator muscles by performing a pelvic-floor or Kegel exercise. Kegels represent a willful contraction of the levator shelf and sling muscles, causing a tightening and lifting of the pelvic supports.
Pelvic Nerves
The big, strong levator muscles of the pelvis, like all other muscles, depend on a healthy nerve supply to maintain their strength, position, and tone.
One nerve in particular—the pudendal—is actually a pair of nerves, one on either side of your pelvis, and is a major power source. These nerves originate in your lower spine and divide into branches that nourish the vaginal area, perineum, and most other pelvic structures crucial to continence and support.
Healthy pelvic nerves are responsible for maintaining pelvic-floor strength, keeping the shelf and sling of the levator muscles (the foundation of your pelvic floor) well toned and healthy.
The pudendals are also responsible for providing sensation to the pelvic area, including around the bladder and bowel as well as sexual. Unfortunately, the anatomical positions of the pudendal nerves—right near the birth canal—make them especially vulnerable to wear and tear in the labor room. Later on, we’ll discuss how injury to the pudendal and other nerves might represent the initial trigger eventually leading to incontinence, prolapse, and other pelvic-floor problems.
Pelvic Connective Tissues and Ligaments
Connective tissue, also called fascia, is a dense, firm, light-colored material encasing the pelvic organs and vagina and helping secure them to the bony walls of your pelvis. Most of the so-called ligaments in your pelvis are thicker areas of this same material. Compared with the levator muscles, which provide the strongest foundation of your pelvic supports, the connective tissues play only a secondary role.
Think of your pelvic connective tissues like carpenter’s glue for your pelvis, helping to secure your pelvic organs as glue would beams of wood, whereas the organs are really held together by the nails and screws of the levator muscles and their nerves.
Despite their secondary status, certain connective tissues do help to keep the pelvic organs in their proper places.
Between the rectum and vagina - A thick layer called the rectovaginal septum separates these two structures, preventing the rectum from bulging up into the vagina. When this layer becomes weak or thin, a rectocele may form.
Within the upper vaginal wall and around the bladder - Connective tissues within the upper vaginal wall provide solid support for the bladder and urethra. When these connective tissues have torn or weakened after pregnancy and childbirth, dropping of the bladder and urethra may occur.
Uterosacral ligaments - These ligaments attach the upper vagina and the lower part of the uterus to the pelvis. When they weaken, prolapse of the uterus and upper vagina can occur.
Conclusion
In essence, childbirth encapsulates both the marvel and the trial of human evolution.
This singular event, which defines the beginnings of life, simultaneously imposes profound physical demands on the female body.
As we marvel at the miracle of birth, we must also acknowledge the toll it takes, often setting the stage for long-term pelvic disorders. The drama of labor, intertwined with the evolutionary intricacies of our anatomy, underscores the resilience and remarkable adaptability of the female body.
Understanding these complexities is crucial as we strive to mitigate the lasting impacts on maternal health, recognizing that every heroic journey into motherhood is accompanied by its own set of challenges and transformations.
Coming Up in Part 2: Unveiling the Secrets of Childbearing Hips
Next, we uncover the critical role of your pelvic shape in childbirth. Discover how the unique width, depth, and space between your pelvic bones can influence labor and potential injuries. Learn about the four classic pelvic shapes—gynecoid, android, anthropoid, and platypelloid—and how they impact your birthing experience. We’ll also reveal how your body prepares for childbirth, the importance of fetal engagement, and the intense physical pressures during labor.
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