The Body Prepares for Labor

Days and weeks before you go into labor, your body is preparing the uterus and cervix for the process. One way to think of this is that the uterus needs to be awakened from its 10-month slumber. It is this process that brings about so many of the symptoms which women experience in the days and weeks before labor.

A primary purpose of the uterus is to contract and push out whatever’s inside. If it does its job before the baby is mature, the problems of prematurity arise. Thus, during pregnancy, the body turns “OFF” the uterus to allow the baby to gestate (grow to maturity) until the baby’s organ systems are mature enough to allow survival outside the mother. For labor to occur, the uterus must be turned back “ON” and primed for its final job.

Although not all the mechanisms are fully understood, it is believed that the class of hormones known as prostaglandins are the catalysts for this awakening process. The prostaglandins are “tissue hormones”…..that is, they are secreted by the same tissue in which they work in (unlike hormones such as the thyroid hormone which is produced in a gland and circulates to many tissues via the blood stream). There are many different types of prostaglandin hormones…..each with slightly different chemical structures and thus, different jobs. Some prostaglandins are responsible for the disappearance of connective tissue in the cervix. When this occurs the cervix softens, effaces (thins out). Ultimately, with uterine contractions, the os will dilate. Other prostaglandins prepare the uterine muscle cells for efficient contraction by making them more sensitive to the hormone, oxytocin, which is produced in the brain. (A synthetic form of oxytocin, Pitocin, is often used to try to induce labor or strengthen uterine contractions during labor.)

Many tissues throughout the body can produce prostaglandins. Prostaglandins are involved in headaches and the pain associated with joint injuries and arthritis. This is why these types of pain may be relieved with drugs such as ibuprofen (Motrin, Advil, etc…) or naproxsyn (Aleve)……these drugs work by blocking the production of prostaglandins. (These drugs should not be taken during pregnancy.) The action of prostaglandins late in pregnancy may also explain the uncomfortable aches that pregnant women feel in the lower back, pelvis, and hips in the days and weeks before labor.

There are also very potent prostaglandins in male semen. This may explain the old wives’ tale that sex may initiate labor. It is certainly the reason that women who are at risk for premature labor are told not to have sex (at least until after the 37th week of pregnancy). It is probable that the uterus and cervix need some minimal preparation by prostaglandins before labor can commence. If you have a medical indication for induction of labor, your clinician may use a tablet or gel form of prostaglandins to prepare your cervix and uterus for labor. The use of prostaglandins in this way, decreases the chance of a “failed induction”. Inadequate prostaglandin preparation prior to labor partially explains the increased rate of cesarean section associated with induction of labor.

In the days and weeks before labor, once the baby is “mature”, your midwife or doctor may offer to “strip your membranes” to encourage your body to make its own prostaglandins. It is well known, that manipulation of “target tissue” will produce prostaglandin release in that tissue. This is one reason why the damaged tissue in sports injuries or back strain create pain (often relieved with anti-prostaglandin synthetase drugs like Advil, Motrin and Aleve). The process of “stripping the membranes” is NOT “rupturing the membranes”…no amniotic fluid is released. It is a procedure during which your clinician attempts to stretch the cervix and disrupt some of the cells in the cervical region which are ultimately bound for “disruption” by labor anyways. Done with a sterile glove by an experienced clinician the procedure is safe, though a bit uncomfortable for the woman. There is evidence that the procedure shortens the time to natural labor by several days.

The Initiation of Labor
Once the uterus and cervix are properly primed, labor is initiated (no one knows exactly how). The uterus starts to contract more rhythmically, more frequently, and with much greater intensity. Most women state that the contractions of true labor are significantly greater than their worst menstrual cramps. It is difficult to give a single example of how labor may start, since there are several variations on the theme. For most women having their first baby, a gradual increase in uterine contractions may be noticed many days before the birth of the baby……stopping and starting several times, giving rise to the phenomenon of “false labor”.

Pregnant women are often not given much credit for this necessary “preparatory phase” of labor since the cervix is not dilating or effacing noticably (the only easily measurable aspect of true labor). But this “latent phase’ of labor is crucial for the end-stage preparation of the cervix and uterus for its grand finale’. Prostaglandins are most certainly doing their thing at the cellular level during this time. Unfortunately, many first-time mothers will have their cervix examined several times over many hours (or days!) only to find that “you are not in labor”.

The truth is that you may not be in the “active phase” of labor (when the cervix is measurably dilating in a short period of time), but your body is certainly doing something that is gaining you headway. Don’t despair during this time. Find ways to keep yourself comfortable and rest assured that your body is doing what needs to be done to prepare itself for active labor. The pregnant body must be allowed this time to awaken and prepare the uterus and cervix for active labor. In many cases, far too much trust is placed in modern medicine’s ability to accelerate this preparatory phase of labor.

Pushing this process before the uterus and cervix are ready is a significant contributor to high cesarean section rates. In the 1970s, the Food and Drug Administration actually added a warning to the label for Pitocin (the synthetic form of oxytocin)- “Not indicated for the elective induction of labor”. This was a warning to the physicians of the time whose overly-interventive style of obstetrics and cavalier attitude about the induction and augmentation of labor gave rise to a tremendous increase in unnecessary cesarean sections…….an attitude that persists in many obstetrical practices to this day.

A common “diagnosis” which is frequently used to justify birth by cesarean section is “failure to progress”…….critics of this overused diagnosis somewhat jokingly refer to it as “failure to wait”, implying that a clinician’s impatience is more the reason for c-section than an actual problem with labor. Many women experiencing what are common discomforts of late pregnancy who enter the preparatory phase of labor days before the actual birth will be diagnosed as being in active labor and then diagnosed with “failure to progress” to justify an end to their predicament. It IS a very difficult situation for both mother and clinician.