The idea that a major storm can cause a pregnant person to go into labor is a widespread cultural belief, often passed down as anecdotal wisdom among midwives and expectant parents. This phenomenon is frequently discussed in the context of dramatic weather events, such as hurricanes, blizzards, or severe thunderstorms. The suggestion is that a surge of deliveries occurs in labor and delivery wards just as the bad weather hits. The persistence of this belief has prompted scientific inquiry into whether external environmental factors, particularly those associated with a storm, can genuinely influence the internal biological timing of childbirth.
The Proposed Mechanism: Barometric Pressure
The primary scientific theory connecting storms to the onset of labor involves changes in the atmosphere’s weight, known as barometric pressure. Barometric pressure is the force exerted by the air above the Earth’s surface, and it typically drops significantly as a low-pressure weather system, like a storm, approaches. The theory posits that the fluid-filled amniotic sac, which surrounds the fetus, acts like a balloon subject to external pressure. When the atmospheric pressure outside the body decreases rapidly, the relative pressure difference across the fetal membranes increases. This momentary reduction in external support is hypothesized to increase the stress on the amniotic membrane, potentially causing a premature rupture of membranes (PROM) in a person nearing natural rupture.
What the Scientific Data Reveals
Research attempting to confirm a consistent link between barometric pressure drops and labor onset has yielded mixed and often contradictory results. Some early studies, including a retrospective analysis of deliveries in Japan, did find a statistically significant increase in both deliveries and ruptured membranes on days with low barometric pressure. However, many other large-scale statistical analyses and observational studies have failed to find a reliable or repeatable correlation. For instance, a study in South Carolina looking at preterm labor admissions found no statistical significance between atmospheric pressure changes and the timing of birth. The difficulty in establishing a definitive link lies in the high variability of localized weather events and the challenge of isolating barometric pressure from other environmental factors.
The Role of Stress Hormones
It is also possible that any observed correlation between storms and increased labor admissions may be explained by the physiological stress of living through a natural disaster. The anxiety, fear, and physical exertion of preparing for or recovering from a major storm can cause a significant increase in the stress hormone cortisol. Cortisol is known to influence the chemical pathways involved in initiating labor. Therefore, the scientific data does not consistently support the idea that barometric pressure alone is a reliable trigger for childbirth.
Established Biological Triggers of Labor
When the external environment is ruled out as a consistent cause, attention turns to the sophisticated, internal biological system that controls the timing of birth. The initiation of labor is primarily a complex, coordinated event involving an intricate dialogue between the fetus and the maternal body. The process is thought to begin when the fetus signals its own readiness for life outside the womb, often linked to the maturation of its organs, particularly the lungs. These fetal signals involve the hypothalamic-pituitary-adrenal (HPA) axis, which increases the production of steroid hormones that cross the placenta. This hormonal cascade triggers a series of biochemical changes in the mother’s uterus and cervix.
One of the primary changes is a functional shift in the effect of the hormone progesterone, which normally maintains uterine quiescence during pregnancy. The uterine muscle also prepares by increasing the number of receptors for oxytocin, the hormone responsible for generating strong, rhythmic contractions. Concurrently, local production of prostaglandins increases to initiate cervical ripening, a process where the cervix softens, thins (effacement), and begins to open (dilation). The coordinated action of these internal hormonal and physical changes, rather than external weather conditions, governs the precise moment of labor onset.