The Three Ps of Labor and Delivery

When a woman goes into labor, a baby is pushed away from her and toward the outside world. Lucky for everyone there is an opening at one end of her womb to allow exit to the waiting obstetrician or midwife. The rest of women have C-sections. What makes the difference between these two groups? The best way for me to explain it is to think of a snappy little maxim I learned on my very first OB-GYN rounds on Labor and Delivery at (formerly) Charity Hospital.

A staff obstetrician re-iterated once again, according to tradition, the concept of the three Ps--Power, Passenger, and Passageway. Basically, this means the force of labor, the size and position of the baby, and the size of the birth canal.

1. The Power

Labor must develop as a series of rhythmic contractions such that a net vector force is out. Irregular contractions and false labor (also called Braxton-Hicks contractions) may become strong enough to become very uncomfortable, but they don't effect enough of an organized force in one direction to push a baby downward and out against the cervix (mouth of the womb). In this way the baby's head cannot act as an effective dilating wedge to accomplish dilatation of the cervix, the criterion used to define the beginning of labor. On the other hand, the force of labor may no longer be enough at the end of long labors. The uterus may become fatigued. The Power needs to be enough to do the job until delivery, and when it can't, cesarean delivery may be the only way.

2. The Passenger

The size and position of the baby are crucial factors in assuring a vaginal delivery. Obviously, if the baby is just too big, we're up against the laws of physics. The proof is in the labor, however, and everyone deserves an attempt at a vaginal delivery, no matter how big the baby is estimated to be. The laws of physics, though, are on our side in pointing the way: Either the baby's going to fit through or not. And if not, we'll know sooner or later. We'll see an obvious slow-down in progress. If we're sure it's not the Power or the Passageway, we know then it's the Passenger.

Position of the baby can affect success also. The head can be angled in such a way such that the widest part is pitted against the narrowest passageway of the bones of the pelvis. And a breech baby may make a vaginal delivery an unnecessary risk.

3. The Passageway

When the Power is good enough (adequate active labor) and the Passenger is not unduly large, the only other risk to a vaginal delivery is the birth canal. The birth canal is a layman's term usually meant to vaguely encompass the pelvis, cervix, and vagina. The pelvis, with it's hollowed out bony architecture, is the most important part. Soft tissue can elasticize to accommodate a baby, but bone will effectively stop a baby, causing head compression and possibly fetal distress. When the Power pushes the Passenger against a small Passageway, labor progress will stop.

Obstetrics is often easy. A baby's going to deliver vaginally or not, and sooner or later the truth will be known. Although the concept of the three Ps is simplistic, it applies when for some reason there's no baby after a time. All the obstetrician need do is go through the three Ps checklist. This only takes three fingers to count, which is fortunate, for the other seven are used to count the other things we worry about. But that is another story.

When Is It Time To Pack The Bags Before Labor?

As you approach your due date, you can become apprehensive about when you should go to the hospital to have your baby. The timing of going to the hospital varies. Certainly a high-risk patient needs to go with any unusual occurrence. A normal pregnant mother need only go, however, when it appears labor is for real. How do you tell?

Labor is defined by obstetricians as a change in the dilatation and thinning out of the cervix, determined by an exam. There are many false alarms, especially in first-timers, when what seems like real contractions fizzle out when monitored in the hospital. The truth is that it's sometimes hard to tell the real thing without a hospital evaluation.

The onset of labor comes gradually, not usually turning on like a light bulb. There are irregular contractions called Braxton-Hicks contractions that can begin around mid-pregnancy. As time goes on, these sequences become more organized, until at the end labor is the final result of the continuum of all of this activity. False labor is nothing more than a peak among the peaks and valleys of early labor; and early labor is the activity twenty-four to forty-eight hours before active labor.

Although the contractions of early labor, also called latent phase of labor, don't do much in the way of dilating the mouth of the womb, they do thin it out and cause the baby's head to descend against it so that active labor will have a yielding target when the real forces begin.

To act as a dilating wedge against the cervix, the infant's head must push against it with a rhythmic force. The force must be sufficient, but the rhythm must be unremitting. A battering ram is a crude yet accurate metaphor. If contractions are irregular, coming first every twelve minutes, then every two, then every sixteen, the rhythm is ineffective. Onset of real labor is more likely with contractions every eight minutes like clockwork, even though this is a longer duration than the two minutes that was part of the disorganized sequence I described first. Therefore, a clockwork rhythm tends to make a better signal for going to the hospital.

Bleeding is never considered normal, except a little spotting after an exam. A pregnant woman should report any bleeding or go to the hospital when it occurs. Luckily, this is a sign of imminent labor, as a dilating cervix sometimes disrupts tiny blood vessels within it.

Rupture of amniotic membranes ("popping the water-bag") is another mandatory reason to check in with a doctor. If fluid can come out, bacteria can get in, and it's only a matter of time before infection can jeopardize a baby and mother. Leaking of fluid carries the same importance. Spontaneous active labor usually begins when this happens, and most deliveries, inductions and otherwise, beat out most infections that may develop.

So the big three signals to get one moving are rhythmic contractions, bleeding, or leakage of fluid. You may still be sent home undelivered, but you did everything right because you followed the rules which say it's better to be sent home many times than to deliver at home.

Induction of Labor--When Is It Right?

One of the questions often asked me in my private obstetrical practice concerns the process of induction of labor. Induction of labor is any process that initiates labor before it might spontaneously begin. It may seem unnatural, the best way to have a baby still being for a woman to go into labor on her own and have her baby vaginally. But it is a completely legitimate technique that is often necessary to bring a pregnancy to a happy conclusion when medical complications in the mother might make continuing a pregnancy dangerous to herself or to her unborn child. This reason for induction is the only medically indicated reason, and it is determined by an obstetrician based on many factors.

Toxemia (now called Pre-eclampsia, or Pregnancy-Induced Hypertension) is a common legitimate indication. A worrisome slowing of the baby's growth might alert a doctor that the outside environment may be less hostile to a baby than the inside environment, or womb (uterus). When these or a host of other dangerous things happen, it's time to have a baby before disaster strikes. Of course, this is really common sense and is usually an obvious conclusion to the mother as well as to her doctor.

But there are also elective inductions. Although it's not the "natural" way to have things go, it is quite acceptable if the prospective mother is within one week of her due date, and her cervix (mouth of her womb) is "ripe" for induction. This "ripening" is determined by how dilated it is, how thinned out it is, and how far down is the baby's head. Certainly a baby within a week of the due date is not a prematurity risk. And a baby who goes beyond the due date may in fact be what's called a post-maturity risk--at risk for fetal distress.

If a patient asks, many doctors will grant a patient's request to induce one week before the baby's due if the cervix is ripe, and most doctors really want to induce if the baby goes much beyond the expected date of delivery. Before the due date is convenient for the patient; after the due date is wise for the sake of the pregnancy.

Many feel that nature should take it's course no matter what. But some patients have domestic situations that justify a safely timed induction. When the father might be available from his work, when a grandmother might be in town to help out, timing delivery before school starts--all of these reasons and innumerable more can cause a patient to ask for an induction. And if she's within that magic week of the due date, a physician will usually consider it, but only if the cervix is ripe. Because if it isn't, a doctor can induce away at an unripe cervix all day, fighting stubborn anatomy. This can increase the risk of resorting to C-section, so it's always wise to follow the rules of ripeness, which are satisfied by a numerical score of dilatation, thinning (effacement), and head descent. This numerical score is called the Bishop's Score and gives obstetricians a raw number value to determine whether induction is feasible or not.

Questions regarding inductions being harder labors than natural labors are valid. The answer is that if an induction, for either medical reasons or personal reasons, is done with a good Bishop's score and within a week of the due date or beyond, it should be no "harder" than a natural labor. Indeed, the patient's own natural contraction mechanism takes over in these cases, allowing a doctor to turn the drip down or even off altogether. On the other hand, an elective induction without an inviting Bishop's Score is a bad idea, as it is liable to be a long drawn out affair, with the shadow of C-section looming continuously overhead when the war against the laws of physics is lost.

Unfortunately, rupture of membranes (breaking the "bag of water") usually necessitates induction, regardless of the Bishop's score, and these patients are at particular risk for failure to dilate and C-sections. This is unfair but at times unavoidable. And although a C-section is a disappointment to those who hoped for an uncomplicated vaginal delivery in these cases, it's not the worst thing that could happen--it's just second choice. But an obstetrician can aim higher than second choice when considering elective inductions merely by following a few easy rules.

The Philosophy of Pain Relief in Labor

Childbirth is a natural event. Because of this, many feel that it should be natural all the way, including no pain relief. To this end, techniques like Lamaze and the Bradley methods have done a lot to help women who choose to get through the experience with that--the experience.

But there are those who really can't do it without a lot of suffering, and often it makes no sense as to who are the ones who can do it and who are the ones who can't. At a certain level, no amount of education or childbirth preparation can make everyone tolerate labor and delivery the same. I've had college graduates with adequate childbirth training choosing to end what they considered intolerable suffering at the beginning of labor; and I've had patients suffering from mental retardation asking me when it was supposed to start hurting near the end. It makes no sense. Why is this?

The easy answer is because we're all different.

Perhaps everyone's pain nerves are different in abundance or distribution. Perhaps different people are more sensitive to different types of pain than others: pressure pain of the baby's head coming down the pelvis, stretching pain of the baby distending soft tissues as descent takes place, bone pain of the baby's skull rubbing against the expectant mother's pubic bone, contracting pain of the uterus (womb) itself. There are many ways pain can contribute to the general discomforts of labor and delivery. Each individual woman is unique in the way all of these causes of pain gang up on her. Natural childbirth techniques, generally successful, cannot always eliminate that one type of pain a woman may be most sensitive to. Let's be fair. Natural childbirth is an ideal for a natural process. But let's not forget that not too long ago dying in childbirth was a natural part of this also. Now I'm not saying that the pain of labor can cause death. What I'm saying, in fact, is that if we're willing to eliminate the "natural" mortality rates associated with childbearing, isn't it fair to eliminate the natural pain in those who feel they can't tolerate it? Because something's natural, does that make it off-limits to a more comfortable experience for the woman who chooses some of the modern methods available, like analgesics and epidurals? The woman who feels she needs something will be the first to tell you her relief is not off-limits.

As an obstetrician I can tell you that all I care about is getting a healthy baby and mother out of all this. Everything else should be the expectant parents' decision--natural or otherwise. There are certain guidelines expected of me to get to my goal, and as far as I'm concerned, the parents are the boss for everything else. Natural birthing methods are a wonderful idea...for some (or even most) women. For others it may be a terrible idea. Yet many who have put in a good faith effort to try it have a lot of pressure on them to try longer than they should. Political correctness has no place in the labor and delivery suite. Methods of labor relief, natural or otherwise, should be made--like voting--behind the private curtain of a parent's wishes. The delivery on one's child should be a memorable event, not an ordeal. Forgive me for saying it again, but it's not how you have the baby, it's how you raise the baby.

Group "B" Strep--As If Pregnant Patients Didn't Have Enough To Worry About

One of the newest "official" concerns of pregnancy is a flimsy little bacterium called Group B streptococcus. Harmless in the vagina of the prospective mother, it could present a significant risk of infection to a baby coming through the birth canal. It is common to find women who are carriers of it. In the mother it is usually without symptoms; in the newborn, it is quite a different story.

Premature rupture of membranes, resulting in complications of premature birth, has been associated with Group B strep in the mother. Also, meningitis can develop in the baby due to a mother's vaginal strep, causing devastating complications or even death to the newborn. It's no wonder that a few years ago the American Academy of Pediatrics invaded the domain of the American College of Obstetricians and Gynecologists by recommending routine screening of all pregnant mothers with a simple swab culture. Soon, most Ob-Gyns began this simple screening method. A Q-tip-like sampler is used to take a gentle swab that is then sent to a lab for growth. Called a "culture," it is usually done at 35 to 37weeks into the pregnancy, and the result is added to the list of items that are already on a prenatal check list.

If the culture is negative, nothing need be done, of course. If the culture is positive, treatment is still not done at that time. This is because the patient is a carrier, meaning if it were treated then, it would only come back. Actually, the value of the culture is in being forewarned. The strep is ignored until time for delivery, for that is the time to eliminate it. The antibiotics are given during labor (usually a simple penicillin will do--or another antibiotic, if allergic), and the baby allowed to deliver normally.

Sometimes strep can present in sneaky ways. Occasionally a woman may have a negative culture but have had a history of a bladder infection caused by this very same bacterium. In my practice, I lump these patients into the same category as ones whose vaginal cultures were positive. I also treat them right then and there, in addition to during the time of labor, because it's not just a "carrier" status I'm noting--it's an actual urinary tract infection in which treatment is indicated.

When a pregnant patient presents in labor without the benefit of a Group B strep culture--if she has had no prenatal care, for instance--the treatment is so simple and safe that an obstetrician and the baby are best served by giving treatment anyway. Since a certain percentage of all pregnant patients are carriers, I often wonder how many patients exposed their babies to Group B strep in the years before it was sought. Yet the infection rate in those years remained extremely low. This is reassuring, for although the one baby that contracts Group B strep meningitis is in grave danger, the chances of any baby actually developing this complication is actually quite unlikely--even in mothers who are carriers. The screening cultures are only another simple item included in modern obstetrical prenatal care.

But there's controversy now. The American College of Obstetricians and Gynecologists advise that cultures, while a good idea, are not crucial in determining those at risk. Instead, this organization recommends treating any pregnant patient as if she had Group B strep when she presents with certain delineated risk factors, like premature rupture of membranes, a fever, or premature labor. Medicolegally, we follow these guidelines and get the cultures. We like to think we're doing everything we can possibly do to stack the deck in our favor toward a healthy, happy baby.

For more information on your pregnancy and labor check out our pregnancy videos.

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