Have you heard the theory that low air pressure during a hurricane can cause a surge in births? Supposedly a steep drop in barometric pressure makes it easier for a baby to pop out. As Hurricane Florence ripped through the Carolinas, we wondered if that was really true.”It’s one of those old wives’ tales,” said Dr. Hal Lawrence, executive vice president and CEO of the American College of Obstetricians and Gynecologists. Yes, a study published in Archives of Gynecology and Obstetrics in 2007 that looked at births at one hospital between January 1997 and December 2003 found an increase in the number of deliveries during periods of low barometric pressure. And another report from 1985 found a significant increase in the premature rupturing of fetal membranes within just a few hours of the barometric pressure falling. But Lawrence says we shouldn’t read too much into them. “The studies show an association between low pressure and an increase in deliveries, but there has never been a study that has shown a causation between low pressure and more births,” he says. However, other problems common in severe storms, such as stress, an abrupt change in daily routine and transportation challenges may be important. Health care professionals in the Carolinas urged their patients to be ready ahead of Florence’s arrival. Expectant mothers at 37 weeks or more near Novant Health Brunswick Medical Center in Bolivia, N.C., were advised to leave the area ahead of the storm if they were able to. “We told our patients close to due date to get somewhere safe and to heed the advice of local authorities,” says Dr. Navin Bhojwani, an obstetrician with Novant Health System’s OB/GYN service in Charlotte, N.C.New Hanover Regional Medical Center in Wilmington, N.C., also told pregnant women at 37 weeks or later to evacuate the area: “It will be difficult to travel to the hospital during the height of the storm, and emergency vehicles may not be able to reach you if roads are blocked by flooding or downed trees.” The medical center advised patients to get their paperwork from their obstetricians before leaving. Onslow Memorial Hospital in Jacksonville, N.C., printed the records for all patients who were 37 weeks and above in case power went out.Patients throughout the region had to make decisions about whether to stay in place or evacuate. The fire department knocked on doors Friday in Hope Mills, N.C., where Amanda Garcia and her husband, Ruben, live, to tell people about a voluntary evacuation. Amanda had been scheduled for a cesarean section on Thursday, but Cape Fear Valley Health System in Fayetteville, N.C., canceled her procedure and advised her to come on Friday. All the beds were filled then, so she was told to come Saturday instead.The couple stayed in town, confident they would be able to get to the hospital. “I got a Jeep; I’m going to make it [to the hospital] no matter what,” Ruben said he thought during the storm.Luckily, fallen power lines and trees didn’t prevent them from getting to the hospital.As heavy rains fell, Amanda gave birth to a daughter, Arlee Grace Garcia, at the hospital on Sunday. In Bolivia, close to the coast, flooding and blocked roads stopped fresh teams of doctors and nurses from reaching the Novant Health Brunswick Medical Center. For five days straight, 187 people worked until some were released to go home Monday. A Novant Health hospital in Charlotte admitted at least one patient who delivered her baby there instead of in Bolivia. Bhojwani, who was on call on Saturday night in Charlotte, noticed a “fairly average” volume of deliveries, despite the weather-related chaos. “When you work in labor and delivery, you think about a big change in pressure, and you prepare for a difference in volume. Anecdotally, we all think about it when we’re in these situations,” Bhojwani says. “But when you actually look at the information out there, it doesn’t support that.”Studies suggest that floods and other environmental disasters “increase the risks of spontaneous miscarriages, preterm births, and low-birth-weight infants among pregnant women,” according to guidance from the American College of Obstetricians and Gynecologists on disaster preparedness for maternity care.”The bigger issue whenever there is a natural disaster like a hurricane, earthquake or flood is that the support systems are in jeopardy,” ACOG’s Lawrence says. When disaster threatens, he says, pregnant women need to make sure they know which health care facilities are open and which ones they can get to.In the end, Lawrence says, speculation about low pressure triggering more deliveries is just one of many ideas about what causes labor. “Having delivered over 6,000 babies, we always talk about what causes labor, what doesn’t cause labor,” he says. “It’s just hard to prove any of that.”Rachel D. Cohen is an intern on NPR’s Science Desk. Copyright 2018 NPR. To see more, visit http://www.npr.org/.