Who Starts Labor? Research Says: Baby Might Be in Charge
Most of us are taught that labor just happens—your water breaks, your body contracts, and the rest unfolds from there. But fascinating research suggests something deeper: in many pregnancies, it’s actually your baby who signals your body that it’s time for labor to begin.
Understanding this natural communication between baby and body can reshape how we think about labor induction, especially for healthy, low-risk pregnancies.
🧬 The Baby’s Role in Starting Labor
Recent research shows that fetal development plays a key role in the timing of labor. When your baby’s systems are mature and ready for life outside the womb, they send chemical messages to your body that help kickstart labor.
Here’s how it works:
1. Fetal Cortisol Surge
As your baby nears full maturity, their adrenal glands release a surge of cortisol—a hormone that helps prepare the lungs, liver, and other organs for life after birth. That same cortisol also signals the placenta and uterus that it’s time to start preparing for labor.
2. Lung Maturity & Surfactant Release
When baby’s lungs are ready, they release a substance called surfactant into the amniotic fluid. This protein helps open the lungs after birth—but it also acts as a messenger, triggering an inflammatory response in the uterus that encourages contractions to begin.
3. Placental Changes
As the baby matures, changes in the progesterone-to-estrogen ratio occur—especially in the placenta. These shifts support uterine activation and help transition the uterus from a quiet state into a labor-ready one.
In other words, your baby, your placenta, and your body are in constant conversation. When everything aligns, labor begins—naturally and in sync.
🧘🏽 Why This Matters for Low-Risk Pregnancies
If labor begins when baby is ready, then waiting for spontaneous labor (when safe) offers baby the chance to complete vital final stages of development, especially in the final days and weeks of pregnancy.
Many people don’t realize that between 37 and 40+ weeks, baby is still:
Growing their brain rapidly
Strengthening lung function
Building fat stores to regulate blood sugar
Refining their suck/swallow/breathe reflex for feeding
Babies born after spontaneous labor at 39–40 weeks are statistically less likely to experience NICU admissions, respiratory distress, or feeding difficulties than those born earlier via elective induction.
⚖️ Rethinking Routine Induction
Some providers now routinely offer induction at 39 weeks for low-risk pregnancies (based on the ARRIVE trial). While induction can be helpful in specific cases, it’s important to ask:
Is this about medical necessity—or convenience?
If baby hasn’t yet signaled readiness, induction may override the natural timing that supports optimal outcomes.
Questions to ask your provider:
Is there a medical reason for induction?
How will we know if baby is ready?
What are the benefits of waiting for spontaneous labor?
What are your beliefs about the natural timing of birth?
🌱 A Different Perspective: Trusting the Process
If we reframe birth as a collaboration between baby and body, we’re reminded that labor doesn’t need to be forced—it can be supported, respected, and awaited. This doesn’t mean all inductions are harmful—sometimes they are absolutely necessary for safety. But in a healthy, low-risk pregnancy, allowing labor to begin on its own gives your baby the time and space to finish essential development and signal that they’re ready.
🧡 In Summary
Your body and your baby are a team. When your baby is ready, they often send the signals that help labor start—naturally and in harmony. For those in low-risk pregnancies, waiting for that signal may support smoother labor, better outcomes, and an easier start to life outside the womb.
Let’s shift the question from “Should we get things going?” to:
“Is baby ready?”
References
Liggins, G. C., & Thorburn, G. D. (1972). Initiation of parturition. In O.G. Edqvist (Ed.), Physiology and Pathology of Reproduction.
Mendelson, C. R. (2009). Minireview: Fetal–maternal hormonal signaling in pregnancy and labor. Molecular Endocrinology, 23(7), 947–954.
Norwitz, E. R., Schust, D. J., & Fisher, S. J. (2001). Implantation and the survival of early pregnancy. New England Journal of Medicine, 345(19), 1400–1408.
Murphy, V. E., et al. (2006). Respiratory distress syndrome and surfactant protein-A in amniotic fluid. Pediatric Research, 60(5), 596–601.
ARRIVE Trial (2018). Labor induction versus expectant management in low-risk nulliparous women. New England Journal of Medicine, 379(6), 513–523.
Spong, C. Y. (2013). Defining “term” pregnancy: Recommendations from the NICHD. JAMA, 309(23), 2445–2446.
