Labor more often begins at night, potentially linked to hormonal changes during this time.
Understanding the Nocturnal Onset of Labor
It's a commonly observed phenomenon: labor seems to begin more frequently during the night. While the exact reasons aren't fully understood, a key factor appears to be the hormone melatonin. According to research [1-4], spontaneous labor in term pregnancies is more often initiated and more babies are born at night.
Melatonin's Role
The Pineal Gland Connection
The night is when the pineal gland secretes melatonin into the circulation. Melatonin receptor expression on the human pregnant uterus has been reported only during labor [5, 6].
Key points about melatonin's potential role:
-
Circadian Rhythm: Melatonin is a hormone that regulates sleep-wake cycles, and disruption of this circadian rhythm has been linked to potential issues.
-
Uterine Activity: It's thought that melatonin could influence uterine contractions. This is because melatonin receptors have been found on the uterus specifically during labor [5, 6].
-
Evolutionary Advantage: It's hypothesized that nighttime labor might have offered evolutionary advantages, such as reduced visibility from predators in the past.
Summary
Labor starting at night is likely related to hormonal changes, particularly the release of melatonin, that happen as part of the body's natural circadian rhythm.
