When Kathryn Higley, head of the department of nuclear engineering and radiation health physics at Oregon State University, learned she was pregnant years ago, she immediately informed her supervisor, who outfitted her with a fetal dosimeter, an iPod-sized personal radiation monitoring system, to attach to her belly.
In the U.S., pregnant women who work in a nuclear facility can be exposed to 50 millirem per month — or about 500 millirem over the course of a full-term pregnancy. “At that level,” says Higley, “nothing will happen to the fetus.”
But the fluctuating levels of radiation near the malfunctioning Fukushima Dai-Ichi nuclear reactors could be more of a cause for concern for unborn babies and young children, who appear to be at greater risk because their cells multiply more rapidly than adults’. In pregnant women, radiation passes via the mother’s blood to the fetus through the umbilical cord. Radiation can also accumulate near the uterus — in the mother’s bladder, for example — and affect the fetus. (More on Time.com: Japan’s Next Nightmare: Health Problems from Radiation Exposure)
The information coming out of Japan changes so frequently that it’s difficult to pin down a specific level of radiation that residents are exposed to; in any case, levels vary from place to place.
Earlier this week, Higley heard a report of 800 millirem at the nuclear plant’s boundary. But taking into account the 12-mile evacuation zone, she says the risk is probably not even as great as the 50 millirems per month that a pregnant nuclear-facility employee is allowed to absorb.
“For convenience, we assume any radiation dose gives us an increased risk of cancer,” says Higley. “But a dose of 10,000 millirem increases the lifetime cancer risk between 1/2 to 1%.” (In the U.S., the Centers for Disease Control and Prevention estimates the typical lifetime cancer risk at up to 50%.)
Yet in areas experiencing high concentrations of radiation, says Higley, “there is no question that really elevated levels do affect the embryo and fetus.”
For that reason, pregnant women and parents of little kids would be wise to heed advisories regarding evacuation zones. Newly pregnant women are particularly vulnerable. They may not even be aware they’re pregnant, yet inside their bodies, the dividing ball of cells, called a blastocyst, is extremely sensitive. (More on Time.com: Radiation Exposure: Fast Facts About Thyroid Cancer and Other Health Risks)
“Early on, any radiation dose at the blastocyst stage is an all-or-nothing event,” says Higley, meaning the blastocyst is thought to either recover and continue growing or miscarry.
According to Duke University’s Radiation Safety Division, rapidly dividing tissues — an embryo or fetus is a good example — are more sensitive to radiation. “Therefore, one could infer that the human fetus, because of its rapid progression from a single cell to a formed organism in nine months, is more sensitive to radiation than the adult,” states a one-page explainer called “A Perspective on Risk to the Fetus from Ionizing Radiation.”
Possible side effects include miscarriage, birth defects, mental retardation and childhood cancers such as leukemia. Poor outcomes are largely related not only to dosage but to a woman’s stage of pregnancy at the time of exposure; first and second trimesters are of the most concern.
At fetal doses less than 1,000 millirem, according to Duke, there is no evidence of harm. Doses between 1,000 millirem and 10,000 millirem incur a low risk of problems, while doses over 10,000 millirem may be linked to lower IQ, retardation and poor academic achievement. (More on Time.com: Radiation May Be a Greater Cancer Risk for Adults Than Doctors Thought)
This week, the New York Times published an email from Douglas Almond, a Columbia University economist who researched the aftermath of the Chernobyl disaster, in which he worries that the Japanese government is not adequately protecting pregnant women.
Almond’s research, published in 2009 in the Quarterly Journal of Economics, examined Chernobyl fallout in Sweden, where radiation levels were considered safe. He wrote:
While this has been largely confirmed in subsequent studies, there is one important exception: children in utero at the time of the accident. Swedish students who were in utero during the accident experienced significantly lower cognitive function, as reflected in performance on standardized tests in middle school, especially those tests that correspond best to IQ.
The damage was greatest for cohorts in utero in regions of Sweden that received more fallout by virtue of rainfall during the time the radioactive plume was over Sweden, and were of gestational age 8-25 weeks at the time of the accident. This last finding mirrors earlier epidemiological analysis of the survivors of Atomic bombings in Japan, which found reduced IQ and head circumference among the cohort exposed to radiation at those gestation ages.
Bottom line: if you’re pregnant and living near the reactor, steer clear of the contamination zone — and then some.