As we have been monitoring the after-effects of the devastating natural disaster in Japan, we have seen a population faced with a number of health risks over the past few weeks. From a health care system in disarray, to shortages of medicine, to a limited supply of food and water, one group in particular that has me terribly worried is pregnant women.

We are beginning to hear reports of the Japanese food and water supply contaminated with radiation - not only in the area where the damaged nuclear reactors are - but also as far away as Tokyo, which is 150 miles from the affected region.

Radiation and pregnancy can be a lethal combination.

The Centers for Disease Control and Prevention (CDC) calls the exposure of a fetus to radiation “prenatal radiation exposure.” This occurs when the mother’s abdomen is exposed to radiation outside the body, or when the mother swallows or breathes in radiation, and it enters her blood stream.

The overall effects of radiation in the general population can include cancer development and organ system toxicity. Human fetuses have rapid cellular metabolism, which is the type of environment where radiation could have significant consequences.

The good news is that the fetus is protected by the mother’s womb, which is able to act as a shield against radiation to some extent. Whatever amount of radiation the mother is exposed to, generally the dose of radiation to the fetus is less than that.

The bad news is that any radiation exposure can be damaging to a developing fetus.

The extent to which radiation exposure can affect the fetus is predicated on two factors: what the age of the fetus is at the time of exposure and how much radiation the fetus is exposed to.

For very early pregnancies, radiation risk is described as an all or nothing phenomenon. Many times, a lot of women that are pregnant miscarry due to the radiation. For those that don’t, there is a chance that there will be no major effect on the fetus.

However, a number of birth defects are possible following exposure. Between two to 15 weeks of pregnancy, radiation exposure equaling more than 500 chest X-rays can cause severe problems for fetal development including stunted growth, deformities, abnormal brain function, or an increased risk for cancer later in life.

Between eight to 15 weeks of development, in particular, a large dose of radiation can put the fetus at risk of brain damage. After atomic bombs were dropped on Hiroshima and Nagasaki, doctors found that babies who had been exposed to radiation at this stage of development showed high rates of brain damage, which generally resulted in lower IQs or even severe mental retardation.

Once the fetus has reached 16 weeks of development, the risks of radiation exposure drop off considerably. While it is still possible for them to suffer from the same birth defects as fetuses in earlier stages of development, it would take a significantly larger dose of radiation for this to happen – the equivalent of more than 5,000 X-rays. A mother who received this dosage would likely be suffering from radiation sickness.

However, this data is mostly based on a one-time exposure. The problem with Japan is that there is the potential for continuous low-dose exposure for a long period of time, and pregnant women may not even be aware of it. The outcomes resulting from this type of exposure will not be known for a long time.

Any pregnant woman who has believes she may have been exposed to radiation ought to consult with her physician right away. In Japan, it is important to make sure that pregnant women are routinely tested for exposure.

Women that are pregnant should definitely adhere to the guidelines that experts have put into place, advising that people stay at least 50 miles away from the nuclear plant disaster. And from an obstetrical and epidemiological point of view, children who are born in Japan over the upcoming months should be monitored for several years to make sure any inadvertent exposure was not damaging to them.

Dr. Manny Alvarez serves as Fox News Channel's senior managing health editor. He also serves as chairman of the department of obstetrics/gynecology and reproductive science at Hackensack University Medical Center in New Jersey. Click here for more information on Dr. Manny's work with Hackensack University Medical Center. Visit AskDrManny.com for more.