Behind the Forecast: Does low pressure trigger labor

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Science Behind the Forecast: Labor vs low-pressure

LOUISVILLE, Ky. (WAVE) - There's an old wives' tale that says that babies are more likely to be born when air pressure drops. Reports from labor and delivery nurses may back up that theory.

First, let's break down how atmospheric pressure changes. Gravity pushes down on our atmosphere giving the air its weight. An atmosphere (atm), the unit of measurement, is equal to the average air pressure at sea level when the temperature is 15°C (59°F). One atmosphere is equal to 1,013 millibars or 29.92 inches of mercury.

At the surface, air pressure can change by adding or subtracting heat. When there's an increase in heat/temperature then energy is transferred to air molecules. The molecules then move faster and bounce against each other which is seen as an increase in pressure. With the colder air, the air molecules slow down which leads to a decrease in atmospheric pressure.

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Another way to change the air pressure, adding or subtracting molecules from an area. An increase in molecules in a region means higher pressure because more molecules pushing on their surroundings. As you climb higher in the atmosphere, pressure decreases since there is less air above you.

Warm air is less dense/more buoyant than cold air, so it rises. When air rises, winds blow inward at the Earth’s surface to replace it, creating an area of low pressure. Low-pressure systems are associated with clouds and precipitation. As storms associated with an area of low-pressure move into a region, the atmospheric pressure begins to drop.

Many of us have heard our parents or grandparents predict approaching rain based on pain their joints associated with lowering atmospheric pressure. Lower pressure has also been known to cause headaches because of pressure differences within the sinuses.

A 2007 study found that lowering atmospheric pressure resulted in an "increase of spontaneous rupture of membranes and increased rates of spontaneous labor." Basically, it found a significant increase in the number of women whose water broke during low-pressure systems.

A 2013 study found that while the storm itself may not cause a woman to give birth, the stress from preparing for and riding through a storm, like a hurricane, can negatively impact the mother and child.

The Chief Nursing Officer at Greensboro, North Carolina hospital with four decades of experience said last year before Hurricane Florence approached the coast that the drop in barometric pressure during a hurricane can induce labor.

Research has yet to definitively find a correlation to spontaneous labor and falling atmospheric pressure.

It’s not just atmospheric pressure drops associated with storms, other weather phenomena can seriously affect a woman’s body during pregnancy. During the hot summer months, hyperthermia, or abnormally high body temperature, is an issue. In the first six to eight weeks of pregnancy, hyperthermia can put babies at a higher risk for brain or spinal defects, according to LiveScience. After this time frame, the threat is lower.

Dehydration can not only cause lightheadedness or dizziness but it triggers the brain to produce a hormone called vasopressin that triggers thirst, Dr. Saima Aftab told LiveScience. Since vasopressin is similar to oxytocin, the hormone that stimulates uterine contractions, dehydration could trigger those same contractions. According to the University of Texas Southwestern Medical Center, while this can be treated by rehydration, sometimes the contractions can lead to preterm labor.

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