Life
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)? Unfortunately, there’s really not one singular trigger responsible for starting the process, as Taraneh Shirazian M.D., OB/GYN at NYU and founder of Mommy Matters tells Romper.
“Immunoproteins get released that start ripening the cervix, that little bit of dilation triggers contractions, then those contractions trigger a whole cascade of events,” she explains.
As the website Midwives Online reported, the medical community traditionally believed that the mother's body caused labor to start. However, there's been a shift in thinking more recently which suggests it's the baby sending those signals to the mother's body. 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 always 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.
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The Baby's Adrenal Glands Signal Labor
As Baby Center explained, 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). The fetal adrenal gland functions like an adult adrenal gland in many ways, according to the American Academy of Pediatrics.
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.
Studies:
Condon, J., Jeyasuria, P., Faust, J. and Mendelson, C., (2004), "Surfactant protein secreted by the maturing mouse fetal lung acts as a hormone that signals the initiation of parturition," Proceedings of the National Academy of Sciences of the United States of America, https://www.pnas.org/content/101/14/4978.full?sid=addd2e9b-c5dc-49e7-9074-2480bad272fa
Experts:
Taraneh Shirazian M.D., OB/GYN at NYU and founder of Mommy Matters
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