Although there are plenty of hypotheses regarding labor and delivery, no one really knows what triggers labor. It's one of life's mysteries, I suppose, and a pretty vital one at that. That being said, there are top theories about what causes labor to start.
Sure it's nice to be surprised by water breaking, but wouldn't it be nice to know what causes you to go from pregnant to parent in a matter of minutes (OK, more like hours)? Not to mention, as people learn more about what triggers labor, women can get a little bit of relief about the labor process. According to a reader's poll taken by Parents, women across the country have varying labor experiences, as they describe what labor really feels like. If knowledge about what to expect doesn't lessen the pain factor, at least it lessens the fear factor.
According to the website Midwives Online, the medical community believed that the the mother's body caused labor to start. However, there's a shift of late that suggests it's the baby that signals to the mother that it's time. In other words, think of the baby acting like a timer letting you know the bun in the oven is ready.
Even though each pregnancy, and birth, is different, there are three stages of labor, noted Baby Center. Labor begins with the dilation of the cervix as it begins to open. This is called early labor. You then move into active labor, when the cervix is fully dilated and contractions come frequently. Finally, the third stage of labor begins when you start to push, and you deliver your baby and placenta. That's all pretty straightforward. But as for what causes labor to start in the first place, read on to discover some of the top theories.
1Mother’s Pituitary Gland Secretes Oxytocin
One theory about what triggers labor is that the mother's body, specifically her pituitary gland, begins to secrete oxytocin when the baby is fully developed and ready to be born, according to Medical News Today. Oxytocin is the hormone that stimulates contractions, reading the cervix for labor. The more mobile the cervix gets, the more the vagina widens, and labor ensues.
2The Baby's Lungs Signal Labor
The theory that the baby signals labor is a shift away from previous theories that postulated that the mother's body triggers labor.
Researchers Carole Mendelson, Jennifer Condon and Pancharatnam Jeyasuria published a study in the Proceedings of the National Academy of Sciences that indicated fetal lungs provide the signal to initiate labor. When the fetal lungs have reached full maturation, they produce a certain type of protein, which in turn sends a wave of prostaglandins through the mother's body that trigger labor. According to Mayo Clinic, the baby's lungs are the last organ to develop in utero.
3The Baby's Adrenal Glands Signal Labor
According to Baby Center, doctors theorize that maturation of your baby's adrenal glands might trigger labor. Although your baby's brain is fully developed in the second trimester, rapid brain development occurs around week 25 to 28. However, it's not until weeks 38 to 40 that your baby's adrenal glands are engaged in what's called the HPA Axis (the interdependent relationship between the hypothalamus, pituitary gland, and adrenal glands). According to the American Academy of Pediatrics, the fetal adrenal gland functions like an adult adrenal gland in many ways. And by the way, even though the adrenal glands are crucial to regulating "survival" hormones that determine flight or fight responses, they are not located in your brain. They're located above the kidneys, but still are an integral part of the HPA Axis.
One theory about what triggers labor is that when your baby's brain functions are on fleek, and that includes having a fully developed HPA Axis, the fetal adrenal glands secrete the hormone cortisol. The release of cortisol in utero causes a hormonal disturbance of progesterone and estrogen, and labor begins.