By Julie Steenhuysen and Jilian Mincer

(Reuters) – While many Miami hospitals are shutting down as Hurricane Irma bears down on Florida, some are offering shelter to their pregnant patients, bracing for the increase in births that often accompanies these large storms.

At least three of the city’s hospitals have plans in place to care for women with advanced or high-risk pregnancies.

They could be busy.

When Houston was hit by Hurricane Harvey, the number of women who gave birth spiked. According to a Memorial Hermann Health System representative, at least five of the not-for-profit system’s 11 Houston-area hospitals with labor and delivery units reported increases in the number of deliveries during Hurricane Harvey. In three, deliveries doubled.

The reason may have something to do with a drop in barometric pressure that accompanies a hurricane. A 2007 study published in the Archives of Gynecology and Obstetrics noted a causal relationship between low barometric pressure and spontaneous delivery.

But overall, the evidence is inconclusive, said Dr. Shannon Clark, an associate professor in the division of maternal fetal medicine at University of Texas Medical Branch in Galveston, on the Gulf of Mexico.

“There’s some studies that show an association and some that don’t. It’s kind of mixed,” Clark said in a telephone interview.

Even so, she said, “It’s still worth it to forewarn pregnant women in areas that are going to get hit that there could be a potential complication.”

In Miami, Jackson Health System alerted women who are at least 34 weeks pregnant or who have a high-risk pregnancy that they may take shelter in one of three of its hospitals, as long as they have registered with the hospital in advance. These women are allowed to bring in one guest, but no pets.

Tania Leets, a spokeswoman for the public health system which serves Miami-Dade County, said they offered the same service last year during Hurricane Matthew.

Baptist Health South Florida offers shelter to women in Miami who are at least 36 weeks pregnant or who have a high-risk pregnancy in one of its four area hospitals. A pregnant woman and one adult companion can set up camp in a waiting room area; those who come must bring their own food, water and bedding. The shelter opens at 8 a.m. on Saturday and closes when the storm has passed, Baptist Health South said in a statement.

Mount Sinai Medical Center in Miami Beach will likewise shelter women who are at least 36 weeks pregnant or those with high-risk pregnancies, according to a statement on its website.

At Memorial Hermann Greater Heights Hospital in Houston, deliveries started to soar two days before Hurricane Harvey arrived, requiring five managers to help with patient care.

“We all know in this business – full moons and storms are a problem,” said Kim Kendall, director of the hospital’s family birth center.

Staff made an effort to close the shades, redirect the conversation and focus on the delivery. “We tried to maximize the experience and minimize the hurricane,” said Kendall.

(Reporting by Julie Steenhuysen and Jilian Mincer; Editing by Richard Chang and Jonathan Oatis)