(Reuters Health) - For years following the events of September 11, 2001 in lower Manhattan, the disaster and its aftermath may have affected women and their babies who were not even conceived yet, according to a new study.

Researchers found that among women who were rescue or recovery workers responding to the events of 9/11, or women who resided below Canal Street in the World Trade Center's neighborhood, those with the most intense exposures to the disaster had doubled rates of preterm delivery and low birthweight babies over the next few years.

"Associations between disaster exposure and adverse birth outcomes have been demonstrated repeatedly in the past," said lead author Carey Maslow, deputy director of research for the World Trade Center Health Registry. "What is surprising is that these associations persisted among infants conceived up to three years after 9/11."

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8 PHOTOS 9/11/2001: 14 most iconic images of 9/11 See Gallery 9/11/2001: 14 most iconic images of 9/11 NEW YORK - SEPTEMBER 11, 2001: (FILE PHOTO) A fiery blasts rocks the south tower of the World Trade Center as the hijacked United Airlines Flight 175 from Boston crashes into the building September 11, 2001 in New York City. Almost two years after the September 11 attack on the World Trade Center, the New York Port Authority is releasing transcripts on August 28, 2003 of emergency calls made from inside the twin towers. (Photo by Spencer Platt/Getty Images) Sarasota, UNITED STATES: TO GO WITH AFP STORY 'Americans mark 9/11 anniversary with new questions on vulnerability' - (FILES) US President George W. Bush has his early morning school reading event interupted by his Chief of Staff Andrew Card (L) shortly after news of the New York City airplane crashes was available in Sarasota, Florida 11 September 2001. AFP Photo Paul J. RICHARDS (Photo credit should read PAUL J. RICHARDS/AFP/Getty Images) Americans mark 9/11 anniversary with new questions on vulnerability' - This 11 September 2001 file photo shows Marcy Borders covered in dust as she takes refuge in an office building after one of the World Trade Center towers collapsed in New York. Borders was caught outside on the street as the cloud of smoke and dust enveloped the area. The woman was caught outside on the street as the cloud of smoke and dust enveloped the area. AFP PHOTO/Stan HONDA (Photo credit should read STAN HONDA/AFP/Getty Images) New York, UNITED STATES: TO GO WITH AFP STORY 'Americans mark 9/11 anniversary with new questions on vulnerability' - (FILES) The rubble of the World Trade Center smoulders following a terrorist attack 11 September 2001 in New York. Americans mark the fourth anniversary of the September 11, 2001 terror attacks Sunday nagged by new burning questions about their readiness to confront a major disaster after the debacle of Hurricane Katrina. AFP PHOTO/Alex Fuchs (Photo credit should read ALEX FUCHS/AFP/Getty Images) 394471 13: Firefighter Tony James cries while attending the funeral service for New York Fire Department Chaplain Rev. Mychal Judge, in front of the St. Francis of Assisi Church September 15, 2001 in New York City. Judge died while giving the last rites to a fireman in the collapse of the World Trade Center. The World Trade Center was destroyed after both the landmark towers were struck by two hijacked planes in an alleged terrorist attack on September 11. (Photo by Joe Raedle/Getty Images) NEW YORK - SEPTEMBER 8: The 'Tribute in Light' memorial as seen from Bayonne, New Jersey, consists of two shafts of light to represent the World Trade Center Twin Towers, is tested before the fifth anniversary of 9/11 terrorist attacks September 8, 2006 in New York City. (Photo by Sylwia Kapuscinski/Getty Images) NEW YORK- SEPTEMBER 3: A wax replica of Thomas Franklin's photograph from September 11, is seen at Madame Tussaud's wax museum September 3, 2002 in New York City. The replica is to be part of an exhibit at the museum called 'Hope: Humanity and Heroism.' (Photo by Spencer Platt/Getty Images) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

The researchers matched birth certificates for infants born in New York City between September 11, 2001 and the end of 2010 to disaster exposure data on women who were enrolled in the World Trade Center Health Registry.

In that time there were 3,360 babies born in the city to women enrolled in the registry. Less than 10 percent of babies were born to women pregnant on 9/11.

Almost 7 percent of the babies were delivered preterm, meaning before 37 weeks of pregnancy, and 6 percent had low birthweight, meaning they weighed less than 5 pounds, 8 ounces.

The average newborn in the U.S. weighs about 8 pounds, and about 8 percent of all babies are low birthweight, according to the Centers for Disease Control and Prevention.

The researchers also looked at the mothers' level of exposure to the disaster and its aftermath - for example, whether they were injured, witnessed traumatic scenes, were evacuated from a residence in the neighborhood, performed rescue or recovery work "on the pile" (of smoldering wreckage), and other types of exposure.

The study team found that through the end of December 2003, women with at least two out of four exposures were 2.3 times more likely than women with less exposure to have a low-birthweight baby and 2.1 times more likely to have a preterm delivery.

Infants whose mothers performed rescue or recovery work were 1.9 times more likely to be born preterm in the first couple of years.

Later in the 10-year study period, differences started to diminish, the researchers note in American Journal of Public Health.

And throughout the study period, babies of mothers with high exposure were not more likely to be small for their gestational age, which was surprising, the authors write.

Physical contaminants and psychological trauma tend to occur simultaneously in a disaster setting, and disentangling their relative effects is very difficult, Maslow told Reuters Health by email.

"Whether the important exposure is posttraumatic stress or components of the toxic dust themselves, the eggs were exposed to it," since reproductive effects appear to persist even for women who were not pregnant at the time of the disaster but conceived in the following year or so, said Dr. Iris Udasin, medical director of the Environmental and Occupational Health Sciences Institute Clinical Center at Rutgers University in New Brunswick, New Jersey.

"The good news is, even though these numbers are higher than we would like them to be, they're not overwhelmingly large," Udasin, who was not part of the new study, told Reuters Health.

It may never be clear exactly how these interactions work, she said.

"Adverse reproductive outcomes have been associated with other terrorist attacks, with environmental disasters, chemical disasters, and even with natural disasters, like hurricanes and earthquakes," Maslow said.

"The real message is, increasing attention to mental health care," Udasin said. "We can't prevent the disaster but we can do a better job of responding to it."

She wouldn't tell women to delay pregnancy after a disaster, but to do everything possible to make themselves healthy, mentally and physically, she said.

"Women who have been exposed to a disaster, including those involved in disaster response, should inform the prenatal care provider of the nature and extent of their exposure," Maslow said.

SOURCE: http://bit.ly/2bSt5db American Journal of Public Health, online August 23, 2016.

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