Understanding Birth and Sphincter Law

Have you ever found it difficult to explain to a physician or to a pregnant woman why some women give birth with ease, whereas others seem to require extraordinary measures in order to give birth? For over half a century, authors of obstetrical textbooks have explained this difference by invoking the so-called 'Law of the 3 Ps', the Ps being the passage (the woman), the passenger (the baby) and the powers (the quality and frequency of uterine contractions). This mechanical explanation has not changed at all over the last 75 years, although the rate of medical interventions in childbirth has increased drastically in most industrialized countries during that same period.

This situation has led some to put forth the hypothesis that the pace of evolution of human beings has suddenly accelerated, in that human heads are said to have become much larger than they were a generation ago, with no corresponding enlargement in the maternal pelvis. This tortured hypothesis is, so far, the only explanation that the scientific community has offered to explain a physiological basis for the trend of increasing medical interventions in the birth.

However, the experience of our midwifery group from the very beginning taught me that the Law of the 3 Ps is essentially flawed, as our experience, like that of all traditional people who have maintained sustainable cultures over millenia, tells us that almost every healthy woman of childbearing age can have her baby vaginally, given the right care and preparation during pregnancy and the correct treatment during labour.

To just consider our first 500 births at the Farm Midwifery Center, for instance, when a woman did need a Caesarean section (only three women did), it was for reasons that had nothing to do with the 3 Ps (a transverse lie and two partially abrupted placentas). The caesarean rate for our first 500 births was 0.6%, counting from the first birth I ever saw and including all of the births that constituted our midwifery training program, which is, I venture to say, not bad for a group of midwives whose formal educations were primarily in English literature and art.

How can the Law of the 3 Ps be considered a law if it apparently was not in effect in the large number of birth we have attended over the years? Our Caesarean rate has never reached 2%, even after we opened the doors of our midwifery center to women who were not members of our community. Our combined rates of ventouse [vacuum extractor] and forceps deliveries amount to less than 0.5%. Surely, if human heads have really increased in size and women's pelvic proportions have shrunk, some of these women would have found their way to our midwifery service in Tennessee, given that we never turned away any woman on the basis that we thought that her pelvic measurements might not permit vaginal birth?

With all of this in mind, I believe that it is possible to articulate a law of birth physiology that better explains why some women give birth easily while others seem to require the assistance of medical intervention. For ease of explanation, I have decided to call it 'Sphincter Law'.

My central thesis is that in those maternity services in which rates of Caesarean section and mechanical deliveries have increased above the levels recommended by the World Health Organization in 1985 (10-15%), the explanation has been—at least in part—the failure on the part of those organizing the services to understand the basics of Sphincter Law (WHO, 1985).

To explain what I mean by this statement, I will start with the observation that the vagina and the cervix—not just the anus and the urethra—are sphincters, that is, the circular muscles surrounding the opening of organs which are called upon to empty themselves at appropriate times. These openings ordinarily remain closed but have the ability to open as widely as needed when necessary. Each of the organs that I have referred to is able to contract rhythmically as it fills, until it reaches the point of urgency that the sphincter relaxes so that urination, defecation, or birth, takes place.

For anyone dealing with or organizing maternity care, probably the most important feature of sphincters to understand is that they function according to several factors:

• Sphincters open best in conditions of privacy and intimacy
• Sphincters open best without time limits
• Sphincters are not under the voluntary control of their owner. They do not obey orders, such as 'urinate now!', 'push!', or 'poop!'
• Sphincters, however, do respond well to praise if there happens to be another person in the proximity of the sphincter's