Authored by Amy Rosenman, MD
The connection between incontinence and childbirth has been assumed for a long time. When gynecologists see women for problems of incontinence, we are not surprised to find the most severe problems often in those women who had many children or who delivered large babies. Recently doctors started working out the details of these relationships and are looking for the specific reasons why some women go on to develop incontinence and other women never have this problem.
As the baby grows, the enlarging uterus causes pressure on the bladder below it. This extra stress on the bladder makes it easier for any additional exertion, such as laughing, sneezing or exercising, to push urine out of the bladder. This is why women who are pregnant often have mild urinary incontinence during pregnancy. During a first pregnancy, more than one-third of women develop temporary stress incontinence. During subsequent pregnancies, more than three quarters develop this problem. However, most of the women who have incontinence during pregnancy return to full continence after delivery as the tissues of the birth canal heal. Only about 5% of these women still have stress incontinence a year after the delivery.
The modern movement of childbirth education is enormously important in helping to educate women about labor, childbirth, breastfeeding and caring for a newborn. Doctors rarely have time to talk with their patients in any detail about the steps of labor and childbirth, and childbirth educators fill this need well. Many childbirth educators also focus on avoiding medical interventions that interfere with a "natural" birth, especially cesarean section. Lamaze, the Bradley method, and many midwives and doctors encourage women to labor as long as needed and as long as the baby's health, as monitored by the heartbeat, can tolerate labor. As a result, prolonged labor or prolonged pushing is sometimes encouraged in order to avoid a cesarean section. However, while safe for the baby, it appears that these concepts may not be in the best long-term interest of the mother. We know now that prolonged and difficult labors may lead to permanent nerve damage and weakening of the pelvic muscles and the supporting structures to the uterus, bladder and rectum. This can eventually lead to dropping of the pelvic organs (known as pelvic organ prolapse) or incontinence.
As every woman who delivers a child knows, labor and delivery subject the body to forces that are not encountered in any other circumstance. Muscles and nerves in the pelvis are especially affected. As the baby's head comes down into the pelvis, it presses against the muscles that line the inside of the pelvis. The farther down the baby's head goes into the pelvis, the greater the pressure against these muscles and underlying nerves. After the cervix is totally dilated, the pushing phase of labor begins. The mother is usually asked to wait for a contraction to start, then hold her breath, and bear down as hard as she can in order to push the baby out. This bearing down presses the baby's head against the mother's muscles and nerves to such an extent that the normal flow of blood is cut off temporarily until that push is over. Without a fresh supply of blood, the tissues are deprived of oxygen and nutrition, making them more susceptible to damage. The pressures generated by pushing are 3 times higher than the tissues would normally tolerate for any prolonged time. However, the few minutes of rest in between contractions usually lets blood flow back to the area. This fresh blood carries oxygen and nutrition to the muscles and nerves and carries carbon dioxide and waste away. The few minutes between contractions are normally enough for the tissue to recover.
However, unless delivery occurs quickly, the baby's head continues to be pressed against the tissues. For some women this pressure can cumulatively add up to many hours. Two nerves, called the pudendal and the pelvic nerves, lie on each side of the birth canal within the muscles that are directly under the baby's head. Because they are so close to the baby's head, these nerves are especially vulnerable to the pressures of labor. The pudendal and pelvic nerves carry the signals from the brain to the muscles that hold the bladder and rectum in place. If these nerves are injured, the signals meant for the muscles around the bladder, vagina, and rectum may not be transmitted properly. Without stimulation from the nerves, the pelvic muscles, like any underused muscle in the body, can become weak and flaccid. Some studies show changes in the function of these nerves in more than half of women following vaginal delivery. Interestingly, a prolonged labor or pushing phase before a cesarean is performed makes it likely nerve damage has already happened even if the baby is eventually delivered by cesarean. Over time and with age, the normal supporting tissues of the bladder, rectum and uterus weaken, adding to the effect of childbirth injury. The result can be incontinence of urine or stool, or prolapse.
Some recent studies show that the likelihood of incontinence and prolapse is lower if the mother (and her doctor) allow the natural force of the uterine contractions to push the baby down the birth canal, rather than have the mother push as hard as she can during this time. If the voluntary pushing part of labor can be limited to less than one hour, studies show a lower incidence of injury to the nerves and muscles of the pelvis. This alternative may be a safer and more natural way to deliver by letting the uterus do the work it was designed to do.
As part of the extraordinary forces on a woman's body during delivery of the baby, the pelvic tissues may be subjected to damage. As the head comes out, the forces can actually tear the ligaments that anchor the pelvic supporting muscles to the pelvic bones. The muscles themselves may also be damaged. Sometimes the muscle near the outside of the vagina is intentionally cut by the doctor to help speed up the delivery. We now know this cut, called an episiotomy, increases the risk of anal incontinence.
For some women these damaged muscles and ligaments remain weak and do not entirely heal. As time goes on and the normal changes of aging and weakening of the tissues takes place, incontinence may result. At present, only sophisticated and expensive tests like MRI or nerve conduction studies can tell if these muscles and nerves have returned to normal. Unfortunately, there is no convenient, easy way at this point for you or your doctor to know if these muscles are weakened and destined to lead to incontinence. Nor is there presently any remedy for nerve damage.
Forceps increases the risk of injury to the nerves and muscles of the pelvis. Forceps are the spoon-shaped metal instruments that are sometimes inserted into the mother's vagina and placed around the baby's head at the time of delivery. These instruments are usually used after a long or difficult labor to help deliver a baby. As the doctor pulls on the forceps, they push away the muscles and soft tissues in the pelvis, allowing more room for the baby to come out. The forceps also help the doctor to pull the baby out, especially if there is a tight fit. However, because the instruments are made of metal and take up space of their own, they increase the risk of stretching and tearing the vagina and supporting tissues of the pelvis. They also put more force against the nerves that run inside the pelvis. As a result, more harm can be done to the tissues, possibly resulting in long-term damage and eventual incontinence.
Because there is a risk of complications with forceps to mother or baby, they should probably not be used to deliver a baby unless there is a rapid drop in the baby's heartbeat, severe bleeding or other emergency that dictates a quick delivery.
The vast majority of women who give birth do not develop incontinence. In most cases, the damage created by childbirth repairs itself over time as the tissues go through the normal healing process. The majority of women experience no residual effect within just a few months after childbirth. Almost half of all women who have a vaginal delivery show immediate recovery of the nerves' ability to carry messages to the pelvic muscles, and 60% will have complete resolution within two months. However, in some women, the injured tissue does not recover 100% of pre-labor strength. For them, the likelihood of incontinence and the discomfort of pelvic prolapse developing later in life are more common.
Labor and delivery may stretch, strain or even tear the muscles and the supporting tissues that hold the uterus, bladder and rectum in their proper place. The nerves may also be stretched and injured, weakening the signals allowing muscles to work properly. Some women have no damage from labor and delivery, some have damage to the nerves; some have damage to the muscles and supporting ligaments; some have damage to every one of these areas.
If injury results from a delivery, the weakened support of the bladder, rectum or uterus may cause dropping of these organs into the vagina. Dropping of any of these organs is called pelvic relaxation, or prolapse. The muscles and supporting tissues that are above the vagina and that hold the bladder up are weakened or torn, allowing the bladder to drop down into the vagina. This bulging of the bladder into the vagina is called bladder prolapse, or a cystocele (see fig 1). The urethra, the tube that you urinate from, can also drop down. This combination of the changes in the normal position of the bladder and urethra and the weakened nerve signals may interfere with the bladder function with resulting urine leakage.
Kegel exercises help to strengthen the muscles in the pelvis. Exercising these muscles during pregnancy has been shown to decrease incontinence during pregnancy and right after delivery.
Likewise, the muscle and connective tissues that hold the rectum in its place under the vagina may be weakened or torn by labor and delivery, which allows the rectum to bulge up into the vagina. The words rectal prolapse or rectocele are often used by doctors to describe these changes in the contour of the vagina. After delivery of a baby, some degree of prolapse is very common. However, in most women these changes heal and resolve within a few months without any treatment. If the problem is severe and does not resolve, some repair might need to be done.
The muscles that lie directly below the vagina and encircle the rectum are the muscles that control bowel movements. During the final phases of labor, pushing the baby through the vagina to delivery, these muscles are subjected to enormous forces and pressures. As a result, injury may occur. Just as for urinary incontinence, there is a higher likelihood of anal incontinence for a woman following a vaginal delivery than following a cesarean section. Studies show that more than a third of women who deliver vaginally have some damage to these anal muscles. In women with a forceps delivery, about 80% have damage to the anal muscles. Injured nerves can also be found in these women. Most recover their pre-labor function, but for some the damaging effects can persist for years. The result of severe injury to anal muscles and nerves can be the inability of the anal muscle to close entirely with resultant involuntary loss of gas or stool.
Just before the delivery of the baby's head, an incision may be made by the doctor in the skin and, sometimes, also in the muscle at the bottom portion of the vagina to allow more room for the baby to deliver. This incision, called (midline) episiotomy, is supposed to avoid incidental tearing of the vagina or rectum as the baby delivers. Episiotomy is a recent practice, devised in order to substitute a straight, clean, easy-to-repair surgical incision for the jagged tear that might otherwise occur. Cutting this incision is also intended to shorten labor by giving the baby's head more room so delivery might be easier and faster. It was thought that faster delivery would decrease the risk of injury to the mother's bladder, and would be gentler for the baby's head. However, studies show no evidence that these assumptions are true.
Much to everyone's surprise, episiotomy may actually cause, not prevent, pelvic prolapse and incontinence, exactly what it was supposed to help avoid. Cutting through the vaginal skin weakens this area and increases the likelihood that the skin will rip further down, possibly tearing into the anal muscle directly below the vagina. If the skin stretches naturally, it is less likely to split apart, and if it does tear, the tear is likely to be shorter. Studies tell us episiotomy may actually lead to more damage of the anal muscles. If injury occurs, control of the anal muscles may be partially lost, and incontinence of gas or stool may result. For these reasons, it is probably best not to have a routine episiotomy at the time of delivery. Women need to discuss episiotomy with their doctors before the baby is due.
Because cesarean section avoids the stretching and tearing of the muscles and nerves that occurs as the baby's head comes through the pelvis, it makes some sense that women who have a cesarean section might have less of a risk of urinary incontinence, anal incontinence and pelvic prolapse. In fact, a few studies show just that. However, most women who deliver vaginally remain continent, so no one is proposing that all women have cesarean sections in order to avoid the possibility of later incontinence. We clearly do not understand all the factors that determine who develops incontinence, so cesarean section would not be necessary in many women with long or difficult labors. With our present understanding, many women would have to have cesareans in order to prevent one woman from developing incontinence. In addition, cesarean section has its own risks including bleeding and possible need for transfusion, possibility of infection, risks of anesthesia and the risk of surgical injury to the bladder or intestines. The prolonged discomfort and recovery from cesarean at a time when the mother wants to be focused on caring for her baby are also not in anyone's best interest.
Studies show that a large baby, a mother with small pelvic bones, a prolonged labor, a baby whose head is in the wrong position during labor, or the use of forceps can be associated with the later development of incontinence. As further research continues to shed light on factors that contribute to incontinence, women should consider discussing potential risk factors with their obstetricians before or during labor. Because the research is still not entirely clear, the subject of preventative cesarean section is controversial, to say the least. Only further research will determine whether obstetricians need to change the advice we give women about labor, vaginal delivery and cesarean section.
There are some things that might be avoided in order to decrease the likelihood that pelvic injury will occur.
Women and their doctors should discuss these issues before labor and delivery and to come to some agreement as to the reasonable choices if a prolonged labor or difficult labor is encountered. Some women may choose to avoid cesarean section at all costs, while others may opt for earlier cesarean section. However, it is time for these conversations to take place. As a patient, each woman can act as both a consumer and advocate for her own health.