"Trust birth" is a phrase that I've commonly heard among those in the natural or home birth advocacy movement. There are even Trust Birth groups springing up advocating this. Such groups may state that trusting birth is natural, and fearing or distrusting birth is unnatural and has simply been taught through our culture. Is this correct? Fear of childbirth has in fact been common throughout history, in all times and cultures. Why? Because while birth is a natural process, it is also naturally a dangerous process. Childbirth in humans is an evolutionary bottle neck, where the advantageous feature of large, well developed brains conflicts with the advantageous feature of narrow pelvises, to aid bipedalism. It is also a complex process, to which no other natural process can be an adequate comparison. Pregnancy itself precariously balances the needs and health of the fetus against the needs and health of the mother. The result is historically high rates of both perinatal (around the time of birth) mortality for the babies involved and maternal mortality. This has the evolutionary purpose of keeping head and pelvis size in check, yet as a human event each loss represents a tragedy. We are not willing to accept the death of a human being as simply "evolution in action."
Improved sanitation and nutrition and modern medicine -- including antibiotics, safer cesarean sections, improved ability to monitor the health of mom and baby during pregnancy and childbirth, and developments in neonatal resuscitation and life support, among many others -- have dramatically decreased the perinatal and maternal mortality rates, although attempts to further reduce it are constantly being made. We now take these improvements in mortality rates for granted. We assume that mother and child will come through birth and be fine. Ironically, it is these very improvements that allow us to assume that birth is low risk and worthy of trust.
If we cannot trust birth, should we then fear birth? Are all interventions good and necessary, with no harmful side effects? Is the best response to make birth a completely medicalized event, attempting to remove all uncertainty? This position forgets that birth, as a natural physiological process, is not fully understood by science. We know of what can go wrong, but still often do not know why it goes wrong. We don't fully understand the purposes of the natural physiology of birth -- we can't know for certain what elements in the process of birth serve a purpose in the health of the mother and child, and we don't always know the long term effects of medical interventions.
I propose the best attitude of a birth attendant is not "trust birth," nor is it "fear birth," but rather is "respect birth." That is, respect birth both as a natural physiological process which goes well much of the time, AND respect birth as a complex event with inherent and natural risks. Birth attendants need both to allow labor and birth to unfold, and to exercise vigilance and intervene when deviations from normal begin to put mother and child at risk. This balance isn't easy, it likely takes significant training both in normal births and potential complications. It means accepting and responding to the scientific evidence on birth practices and interventions without prejudiced ideology. It means abandoning simple catch phrases or black and white positions and truly grappling with what we know, and what we don't know.