Birth is often a mystery—at least that’s what we’re led to believe. But closer examination reveals basic physiological truths that underpin normal birth for both the mother and baby. Certain truisms can indicate risk, such as a pregnant woman’s prenatal nutrition and medical history, but, in the end, birth is a complex orchestration of hormones, proteins, neurology, and basic psychology for the mother. The teasing apart of these elements allows us to understand the perfectly designed biological process of childbirth.
What We Know About the Onset of Labor
There is surprisingly little known about what causes labor. In the beginning of pregnancy, the woman’s immune system is suppressed to insure that the forming embryo implants successfully and the biological process sets in motion. In fact, if a woman’s immune system is too active, miscarriage can occur in the early months. Later in the pregnancy, when the baby is full term and labor begins naturally, though, there is less consensus about the exact cause of labor. Science is only just beginning to understand the onset of labor.
There’s strong evidence the baby may have something to do with initiating labor. When the baby reaches 32 weeks, a surface protein, a soap like substance or surfacent, coats the inside of the baby’s lungs to keep the alveoli open, a critical shift that will allow the baby to breathe outside the uterus. The surfacent consists of six fats and 4 proteins and continues to be produced until around the child’s eighth birthday, when the lungs are fully developed. Eventually one of the proteins, SP-A, is produced in the baby’s maturing lungs in utero. This protein activates immune cells (macrophages) to migrate to the uterine wall, creating a chemical, inflammatory, reaction, which may be the official start of a natural labor. Studies have been done with mice in which the SP-A is blocked; the mice remain pregnant beyond normal gestation. So, in a nutshell, the baby’s development—more importantly, the baby’s maturing lungs that signal when they are ready to breathe outside the uterus—may be the instigator, signaling for labor to begin.
On the mother’s part, hormones play an important role. Prostaglandin is the hormone that softens the cervix and oxytocin increases and triggers contractions. Also at play are estrogen, progesterone, cortisol, and CRH—corticotrophn. When the baby drops in the mother’s pelvis, the hormones assist, and the cervix begins to relax and thin.
The hormones; the baby’s position; and the immune cells, in concert with the uterus, all work together to trigger the full onset of labor. And hormones continue to work to the mother’s advantage as she progresses through the rest of the labor.
Hormones in Undisturbed Labor Defined
Any woman who has had a natural birth or observed a natural birth knows that undisturbed labor is intuitive and powerful, an intricate dance between mother and baby and the people assisting the mother. The mother often knows what she most needs, even in the most complicated of situations, because of the uninterrupted intuitive interplay between mother and baby.
Sarah Buckley, MD, an Australian obstetrician, writes and speaks extensively on the hormones at play in undisturbed birth. The key hormones in birth include oxytocin, beta-endorphin, adrenaline (epinephrine), and noradrenaline (norepinephrine), and are identical to the pattern of hormone release in lovemaking. “As the hormones of love, pleasure and transcendence, excitement, and tender mothering, respectively, these form the major components of an ecstatic cocktail of hormones that nature prescribes to aid birthing mothers of all mammalian species,” Buckley writes in “Gentle Birth, Gentle Mothering.”
The cocktail of hormones build up and peak around the time of birth or soon after and subside and reorganize over the hours and days after the birth. All of these hormones are produced primarily in the hypothalamus and each serve an important function in natural labor: oxytocin, the love hormone, stimulates contractions, and higher levels of oxytocin are also beneficial for contracting the uterus after birth to prevent hemorrhaging; beta-endorphin serves as a stress hormone, more specifically as a pain-reliever that in high amounts can slow the production of oxytocin, thereby helping to modulate the pain of labor; and adrenaline and noradrenaline—fight or flight hormones—rise at the end of labor, giving the mother extra energy for the pushing and initiating the ejection impulse necessary for the final stage of labor.
Karen Strange, CPM, who teaches NRP training from the baby’s perspective, teaches birth workers to observe and expect the laboring mother to “pause” after the baby arrives. Strange teaches that there is a natural sequencing to birth for both mother and baby, and the pause or resting allows them to have a time of integration. Oxytocin, the love hormone, is at its highest in the hour after the birth, and mothers and babies begin the bonding process during that sacred hour. But noradrenaline also plays a role. “Noradrenaline, as part of the ecstatic cocktail, is also implicated in instinctive mothering behavior. Mice bred to be deficient in noradrenaline will not care for their young after birth unless noradrenaline is injected back into their system,” writes Buckley.
Why Environment Matters
Michael Odent, French obstetrician and surgeon, studied the environments for birth in the 1980s. He introduced low lighting, birthing pools, and singing into the birthing rooms at the hospital where he practiced in Paris. Eventually he became involved in home birth and started a research center in London. He found that low lighting, less observation, warm water, and a more homelike environment aided women in labor. Looking at the hormones at play—the very same hormones that are involved in lovemaking—it’s easy to see why a woman’s labor might be aided by the elements he studied. Traditionally women have birthed in a home, or even outside. The hospital environment became a new normal in the 20th century as surgical and other interventions began to rise, an environment Odent refers to as the masculinization of the birth environment.
Buckley writes, “For birth to proceed optimally, this more primitive part of the brain needs to take precedence over our neocortex—our “new” or higher brain—which is the seat of our rational mind. This shift in consciousness, which some have called “going to another planet,” is aided by (and also aids) the release of birthing hormones such as beta-endorphin, and is inhibited by circumstances that increase alertness, such as bright lighting, conversation, and expectations of rationality.”
Finely Tuned Dance
Low lighting, quiet, and support for the increasing irrational and more instinctual feelings of the birthing mother all support undisturbed labor. Midwives are trained to follow the mother. By following her cues and trusting in the complex orchestration of hormones, the healthcare provider receives vital information for understanding how the labor is progressing. What is most important is that the mother feels safe to travel to that other planet and that labor starts naturally and remains undisturbed. Biology most often takes care of the rest.
The physiology of birth includes a finely tuned dance between mother and baby, between immune cells and proteins and the uterine wall, and between the mother and her environment. If birth is treated more like a medical procedure, more like a masculine [refers to culture, not to men specifically] and rational endeavor, the more removed the mother will become from all the benefits nature provides. The physiology of birth, when allowed to proceed uninterrupted in normal birth, provides a hormonal roadmap for a successful birth and bonding.
“Giving birth and being born brings us into the essence of creation, where the human spirit is courageous and bold and the body, a miracle of wisdom.”
-Harriette Hartigan, midwife, author, and photographer