The earth’s atmosphere blocks most cosmic rays, but at higher altitudes exposure increases. Nonetheless, pregnant women who occasionally travel by air can be assured that the harm to their fetus from cosmic radiation is negligible, according to a new report.

However, on the rare occasion of a solar-particle event or solar flare it is possible to be exposed to a potentially harmful dose of radiation, the authors warn in the medical journal Obstetrics and Gynecology.

The Space Environment Center (SEC) of the National Oceanic and Atmospheric Administration maintains a Web site with real-time data on when a solar flare is occurring. Pregnant women can check this Web site and, if necessary, postpone their flight by a few hours until the high-dose period has passed (http://www.sec.noaa.gov).

Also, the US Federal Aviation Administration (FAA) and the SEC has recently introduced an alert system that sends a warning to at-risk airlines to lower their altitude to a level with less radiation exposure. This is meant to protect those pregnant women who are already in the air when a solar-particle event occurs.

At present, it is recommended that radiation exposure not exceed 1 millisievert (mSv) over a 40-week pregnancy. While this 1-mSv limit is a law in Europe, it is only an advisory in the US. Most research has suggested no evidence of fetal harm with exposure levels below 20 mSv.

On a trip from New York to Seattle, for example, passengers are typically exposed to 60 microsieverts, or 6% of the maximum recommended dose; the exposure goes up to 150 microsieverts on an intercontinental flight from New York to Tokyo.

The radiation risk for pregnant women who fly on a more regular basis, such as crewmembers and frequent business travelers, requires a more detailed analysis, study author Dr. Robert J. Barish, from The Lenox Hill Heart and Vascular Institute in New York, notes.

For these women, the FAA has created software, accessible on the Internet, which can calculate the in-flight radiation dose on a trip-by-trip basis. Coupled with the recommended dose limits, the software should help women decide how much flying they are comfortable with, he adds.

SOURCE: Obstetrics and Gynecology, June 2004.