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."

More on this...

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.