Pregnant women who were around New York's World Trade Center during the September 11, 2001, attacks didn't have a higher risk of giving birth to premature or low-weight babies, researchers said on Tuesday.

While controversial studies suggest that the attacks continue to trigger health problems for tens of thousands of people exposed to the horrors and dust of that day, it had remained unclear if they also took a toll on babies still in the womb.

There were two studies prior to this one that suggested there may have been a small effect, said Dr. Thomas Matte, whose findings appear in the journal Obstetrics and Gynecology.

Overall, we aren't seeing a substantial difference in birth outcomes for these women, said Matte, from Hunter College of the City University of New York. That should be somewhat reassuring.

He added that the new research included more women than earlier studies.

The researchers tested birth outcomes among 446 women who had been near the World Trade Center on 9/11 and had been pregnant during the attacks or in the following three months.

Since these women had higher incomes than most New Yorkers, they compared them to a large group of women who weren't in Lower Manhattan. They excluded all women on Medicaid insurance.

After accounting for normal seasonal variation and other factors that influence birth outcomes, there was no difference in either birth weight or premature deliveries.

The researchers did find that among the 446 women exposed to the attacks, those who said they suffered from the symptoms of post-traumatic stress disorder had more low-weight and preterm babies than women without stress symptoms.

Although those findings are in keeping with earlier research, Matte said, We can't say that we can absolutely with certainty attribute what we are seeing to a cause and effect relationship.