Nobody ever said that life would be easy or worry-free. But could there be any match for the emotional stress a fetus might feel, lying in the womb the night before beginning its journey through the pelvis?
Our in-utero friends face a struggle of epic proportion on their way out—the equivalent of a slow train ride through a tunnel that’s narrower than the train itself. But fetuses are equipped with several remarkable features that ease their journey, including soft spots between skull bones that actually bend and overlap (molding), naturally lubricated skin, and that well-known cone-head shape that narrows the width of the baby’s cranium. Like a good Boy Scout or Brownie, a fetus arrives in the labor room prepared.
The changes that occur within Mom’s pelvis are equally impressive. Throughout the nine months of pregnancy, the lower half of your body takes a number of steps in an effort to prepare itself for the big task ahead.
First, changes occur to the soft tissues of your pelvis. The vaginal walls become significantly thicker as the stretchy smooth muscle enlarges and the usually firm connective tissue layer softens. While these changes cause the vagina to become longer and thicker, there is also a steady increase in vaginal secretions and natural lubrication, which enables your soft tissues to stretch out of the way.
Perhaps more surprising are the changes taking place with your pelvic bones. A special hormone produced by the ovary during pregnancy, appropriately named relaxin, appears to cause relaxation and some expansion at the pelvic joints. The pubic symphysis, which is the connective tissue connecting the bones right at the front of your pelvis, becomes mobile and wider—these pubic bones can separate (diastasis) up to several centimeters in some women! Also, the sacroiliac joint, connecting the side bones of your pelvis to your lower spine, becomes more mobile. When your hormone levels return to normal after birth, the pelvic bones return to their original rigid state. But as your body anticipates the evolutionary mismatch of a lifetime, these changes are taking place to reduce your odds of physical harm.
Your Due Date Arrives — Are you Engaged?
“Has the head dropped yet?” It's a question asked by many women during their last month or two of pregnancy. But what does this question actually mean? As your due date nears, the baby’s head often lowers itself into the bony pelvis. When the widest part of the fetal head secures itself within the pelvic cavity, the fetus has become engaged, in obstetrical terms.
Some women may suddenly feel they’re able to breathe more easily, since they’ve begun to carry lower. Others notice increased urinary frequency and constipation as the fetal head creates more pressure in the pelvis.
Engagement does not always occur before your first labor begins; one study conducted by midwives found engagement in only 31 percent of first-time mothers-to-be, though most other estimates have been higher.
Nevertheless, when engagement does occur in a first pregnancy, many practitioners consider it a sign that a good fit exists between mother and baby, perhaps reflecting an easier labor and delivery ahead. In subsequent pregnancies, when the pelvic tissues are more lax, an unengaged fetus at the onset of labor is not considered a prognostic sign.
But what if you’re past the due date of your first pregnancy and the baby’s head is still floating up above the pelvic bones, unengaged? According to some obstetricians, this might represent the first warning that your pelvic shape and your baby’s head aren’t the world’s most ideal fit; there is data to show that you might be at higher risk for a labor that fails to progress to a successful vaginal delivery.
One recent Johns Hopkins study of more than twelve hundred women carrying their first pregnancy showed the risk of cesarean section nearly tripled if the baby’s head was not engaged when active labor began. Another study found that a floating fetal head conferred longer second stage of labor (the time from being fully dilated until delivery) and increased the risk of cesarean from 6.9 to 27 percent. Other studies have contradicted these findings, concluding that engagement might not be a very reliable predictor of a successful vaginal birth. Many practitioners disregard the issue of engagement, claiming equal success at achieving vaginal delivery even if the fetal head is floating.
What does all this have to do with your pelvic floor and postreproductive body? It’s a matter of what efforts are required to achieve vaginal delivery and how these efforts might impact your body. Delivery of an unengaged fetus might take considerable extra effort and reduce your odds of an easy vaginal birth. But deciding whether this extra time and effort creates more risk of physical injury to you is not usually clear. Engagement is just one measure of maternal-pelvic fit, which has prognostic value only during your first pregnancy and can’t flawlessly forecast an easy versus a traumatic delivery. The significance of fetal engagement remains a question that future research will hopefully help to resolve.
Labor—The Pelvis Under Pressure
Finally, labor begins. Obstetricians and midwives divide labor and delivery into two stages, and acquainting yourself with them can help you understand how childbirth might affect your body.
Labor’s first stage begins when your uterine contractions become painful and frequent, and the cervix begins to dilate—that is, to open. It ends when the cervix is fully dilated at ten centimeters. The first stage of labor requires patience—during your first pregnancy, reaching just four to five centimeters can take up to twenty hours from the time your labor contractions first begin. Most women remain at home during the early part of this stage; after arriving at the maternity unit, some may rest with the help of pain medication, while others walk the hallways or even lie in a warm bath.
However they’re laboring, most women are focused on one central question: “Am I ten centimeters yet?”
When you do reach ten centimeters—or, more precisely, when the cervix is fully dilated—you’ve entered the second stage of labor. This stage ends with the delivery of your infant. Its duration ranges from around two hours for a first delivery to only twenty minutes for women who have had previous vaginal births.
When the second stage begins, one of the first things you’ll notice is more intensive monitoring by the doctors and nurses of both your labor progress and your baby’s well-being. The beginning of the second stage is usually when you’re instructed to start pushing, the most physically stressful part of labor for both baby and mom. Fully dilated might accurately describe the cervix as the second stage begins, but it’s not true for the rest of your pelvis. A tremendous amount of dilation throughout the pelvis has yet to occur, and the majority of fetal descent still lies ahead.
Along the way, as this dilation and descent take place, stretch and compression affect the vagina, bladder, urethra, muscles, and nerves. When you push, all of these forces are magnified.
Pressures generated between the fetal head and vaginal wall can average 100mmHg and reach peaks of 230mmHg.
For those of you without an engineering or physics background, rest assured that this a remarkable force in biological terms. A force of only 20 to 80mmHg will stop the flow of blood in most human tissues, and can damage them beyond repair if applied for a prolonged period. As you can imagine, forces up to three times that intensity, within the narrow confines of the pelvis, might change nearby structures.
Aim your telescope at childbirth drama during labor’s second stage, and you’ll observe a true irony within modern women’s health care: a monitored fetus and a sometimes overlooked mom. You’ll see most eyes in the modern delivery suite—including those of the health-care team, the mother, and her partner—trained on the squiggly lines of the fetal monitor from the start of the pushing, squatting, and “hut-hut-hooing” to the baby’s first cry. All the while, the maternal pelvic changes, which can affect some women for a lifetime, may escape the gaze of all the players on childbirth’s stage. Arguably, the potential effects of labor on the maternal body are among the most neglected topics in women’s health.
In later posts, we'll talk about the ways you can help yourself—through prenatal preparation, pushing techniques, avoidance of risky procedures, and so on—making it less an event of chance and more a process of choice.
Conclusion
Childbirth is a magical experience for women and their partners. Unfortunately, doctors and midwives are not magicians! Guiding a baby through your pelvis is far trickier than pulling a rabbit out of a hat, and the problems that you can be left with are not entertaining. Once you understand your postreproductive body, you’re on track to improving your heath, relieving your symptoms, and possibly even preventing future ones.
Coming up Next: The Pelvic Floor After Childbirth
You’ve become aware of the pelvic floor, an important area of your body that you may not have known before. You’ve learned that it looks a certain way before childbirth and another way afterward. With this new “pelvic perspective” in mind we will examine how various obstetrical events and procedures can affect your function afterward, and what to do when things go awry. Our next few blog posts will provide you with countless tricks of the trade from the expertise of Altyx co-founder, Dr. Roger Goldberg.
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