Warning: Ionizing Radiation IS a Teratogen!
What is a teratogen?
A teratogen is any environmental factor with the potential to cause birth defects during prenatal development if absorbed by the mother during pregnancy. The severity of the defects depends on the intensity and duration of the exposure to the teratogen.
What is ionizing radiation?
Ionizing Radiation is any radiation, as a stream of alpha particles or x-rays, that produces ionization as it passes through a medium. (Dictionary.com) It penetrates tissues deeply and has the potential to alter living cells.
What are possible sources of ionizing radiation?
Humans are exposed to natural sources of ionizing radiation in day to day life. These come from cosmic rays, soil, and air. However, exposure to this type of radiation is not sufficient to cause teratogenic effects, and one must be exposed to intense levels of other types of radiation in order to see the effects on the fetus. Other sources are X-Rays, Nuclear Reactors, radiation, therapy machines, atomic bombs and radioactive isotopes.
When are the critical periods during pregnancy that ionizing radiation could affect the fetus?
During the first 2 weeks of pregnancy, the embryo is very resistant to malformations caused by ionizing radiation, however it is more sensitive to the lethal effects of radiation. While radiation can have teratogenic effects throughout the entire pregnancy, the most critical period is between 8 and 15 weeks after conception. As this is the period when the nervous system is developing, the fetus is most vulnerable to radiation-induced central nervous system damage which could then lead to mental malfunctions. Birth defects associated with organs can be effected during the first 10-80 days after conception of the fetus.
The critical period for being at risk for cancer is slightly different. Radiation can also lead to an increased risk of childhood cancers, especially leukemia. The most sensitive period of radiation exposure for leukemia is during the 7th week, but for all other cancers the first 6 months are when the fetus is most at risk for development from radiation exposure.
What are the levels of ionizing radiation that could affect the fetus?
Radiation is measured in Grays or Rads, with 1 Gray equalling 100 Rads. It is a dose-dependent teratogen, meaning that it is not a teratogen at normal levels of exposure (on a typical day-to-day basis). Generally, larger than .1 Gray is cause for concern of teratogenic effects on the fetus, which is enough to kill a preimplantation embryo in many cases. 500 rads (5 Grays) is the dose necessary to kill all fetuses or human embryos before the 18th week after conception. In the early 1900s X-Rays were used to abort the fetus because they exposed the fetus to radiation, and one dose of 360 rads was enough to kill the fetus. 1 Gray received during the 8th-15th week can cause a decrease in average intelligence by about 30 points in school performance. Generally, the radiation received from an X-Ray or CT-scan or other typical clinical procedures isn't sufficient to do damage to the fetus, but as research is not conclusive on the effects of radiation pregnant women should avoid receiving any radiation that is not associated with a procedure that is critical to their health. It's important to note that level of radiation is measured by what is exposed to the fetus, which is generally much less than what the mother is exposed to as the uterus acts as a protective measure.
What could result if exposed to a high level of ionizing radiation during pregnancy?
- The fetus may experience impaired cell division, cell death, mutations, growth impairments, malignancy, and chromosome fragmentation.
- microcephaly (congenital malformation)
- The brain and eyes are severely affected
- small head
- mental retardation
- Many pregnant women that are exposed to radiation may miscarriage or have still births
- fetal growth restriction
- There is an increased risk for childhood cancer (especially Leukemia)
Table 1: Potential Health Effects (Other Than Cancer) of Prenatal Radiation Exposure
|
Acute Radiation
Dose* to the
Embryo/Fetus
|
Time Post Conception |
| Blastogenesis
(up to 2 wks)
|
Organogenesis
(2 –7 wks)
|
Fetogenesis |
| (8–15 wks) |
(16 –25 wks) |
(26 –38 wks) |
| < 0.05 Gy (5 rads)† |
Noncancer health effects NOT detectable |
| 0.05–0.50 Gy (5–50 rads) |
Incidence of failure to implant may increase slightly, but surviving embryos will probably have no significant (noncancer) health effects |
• Incidence of major malformations may increase slightly
• Growth retardation possible |
• Growth retardation possible
• Reduction in IQ possible (up to 15 points, depending on dose)
• Incidence of severe mental retardation up to 20%, depending on dose |
Noncancer health
effects unlikely |
> 0.50 Gy (50 rads)
The expectant mother may be experiencing acute radiation syndrome in this range, depending on her whole-body dose. |
Incidence of failure to implant will likely be large,‡ depending on dose, but surviving embryos will probably have no significant (noncancer) health effects |
• Incidence of miscarriage may increase, depending on dose
• Substantial risk of major malformations such as neurological and motor deficiencies
• Growth retardation likely |
• Incidence of miscarriage probably will increase, depending on dose
• Growth retardation likely
• Reduction in IQ possible (> 15 points, depending on dose)
• Incidence of severe mental retardation > 20%, depending on dose
• Incidence of major malformations will probably increase |
• Incidence of miscarriage may increase, depending on dose
• Growth retardation possible, depending on dose
• Reduction in IQ possible, depending on dose
• Severe mental retardation possible, depending on dose
• Incidence of major malformations may increase |
Incidence of miscarriage and neonatal death will probably increase depending on dose§ |
|
|
Center for Disease Control
How can I protect myself from ionizing radiation poisoning?
- It is impossible to completley avoid exposure, as people are exposed to natural sources in everyday life (from the soil and cosmic rays), however there are ways to minimize it. It's important to reduce the amount of time you spend exposed to radiation as much as possible by only receiving the exposure that is necessary. While some x-rays are essential to be had, if you are pregnant you should only have x-rays taken that are immediately necessary to prevent doing damage to the child.
- the intensisty of radiation decreases, the further you are away from the source
- certain barriers help to protect from radiation, for example, certain lead, concrete, water, or plastic
FAQs for Pregnant Mothers Concerned about Radiation Exposure: http://hps.org/publicinformation/ate/faqs/pregnancyandradiationexposure.html
Examples of exposure to ionizing radiation as a teratogen:
1. Hiroshima/Nagaski
VIDEO:http://www.youtube.com/watch?v=0n1rqHo4XyM&mode=related&search=
- On August 6, 1945 an atomic bomb was dropped on Hiroshima, Japan and instantly killed 100,000s of people
- Three days later, on August 9, 1945 a second atomic bomb exploded over Nagaski, Japan taking over another 100,000 lives
- When an atomic bomb is released it causes extreme heat of about roughly a million degrees celcius burning everything in sight, a very high atmospheric pressure generating blasts destorying everything in its path, and release of radioactive rays
- Most of the women that were exposed to the atomic bomb between their eigth and fifteenth weeks of pregnancy had miscarriages or stillborns
- The babies that did survive endured growth defects, mental retardation, smaller head size, and microcephaly
- Studies have been able to link the incidence of birth defects with the distance of the mother from the explosion of the bomb. Those mothers who were exposed to radiation (between 50 and 100 rad) had a higher frequency of children being born with born defects
2. Chrenobyl
http://teratology.org/updates/60pg100.pdf
On April 26, 1986, in what was the soviet union at the time a reacer exploded in the CHernobyl nuclear power plant, releasing large amounts of radiation. The fire that resulted from it sent waves of radioactively contaminated fallout into the atmosphere and across the surrounding geographical areas. The blast contaminated large areas in Ukraine, Belarus, and Russia and many people from the places directly surrounding Chernobyl were forced to evacuate. While it is certain that many people died as a direct result of this blast, the soviet-era cover-ups forbade doctors to cite Chernobyl as a cause of death for most cases. "The radiation levels in the worst-hit areas of the reactor building have been estimated to be 5.6 röntgen second (R/s), which is equivalent to 20,000 röntgen per hour (R/h). A lethal dose is around 500 röntgen over 5 hours, so in some areas, unprotected workers received fatal doses within several minutes" (Wikipedia). However, at the time no one had any way of telling what the surrounding radiation levels were. Immediately following the incident, many people termed people's fear of possible health issues stemming from the exposure to radiation as simple "radiophobia," brushing it off as something that was no big deal. For this reason, there is much unknown as to what exactly was a result of the explosion and what wasn't. Many of the factory workers died as they had been exposed to lethal doses of radiation, but it also had severe effects on those who were not in direct proximity to the explosion. Many children born after Chernoybyl (who would've been between 8-15 weeks gestation during the explosion) were later born with severe birth defects, mental retardation, and other conditions that have shown to be correlated with radiation exposure. In Ukraine, the rates of neural tube defects were the highest in those areas directly affected by the Chernobyl explosion.
Child born with birth defects because of radiation resulting from Chernobyl
3. CancerTreatment: -About one in every 1000 pregnancy's coincide with cancer. Most pregnancies battling cancer are reccommended to be terminated, however it is possible to deliver a full term healthy baby.There are many different types of cancer prevelant in our society today, the one's most often associated with pregnancies are breast cancer, cervical cancer, lymphoma, and thyroid cancer. Less common, but still seen are leukemia and melanoma.
Potential side affects of in utero radiation exposure on a developing fetus: prenatal death, intrauterine growth restriction, small head size, mental retardation, organ malformation, and childhood cancer.
Specifics about Radiation Therapy: Certain tests, such as ultrasounds and magnetic resonance imaging (MRI) scans, do not expose the fetus to radiation. However, the contrast material sometimes used in MRI has been linked with fetal abnormalities in lab animals. For this reason, contrast-enhanced MRI is not recommended during pregnancy. Chest x-rays involve a small amount of radiation. They are generally considered safe when the abdomen is shielded. Other tests, such as bone scans or computed tomography (CT) scans of the chest, abdomen, or pelvis, are more likely to expose the fetus to radiation. In rare cases when these scans are needed, doctors can adjust the way the test is done to limit the radiation exposure of the fetus as much as possible. The most common procedure practiced with breast cancer is a lumpectomy or partial mastectomy during the pregnancy, folllowed by radiation therapy after the baby is born.
Experiments done (links)
1.) Isaacs RJ, Hunter W, Clark K: Tamoxifen as systemic treatment of advanced breast cancer during pregnancy--case report and literature review. Gynecol Oncol 80 (3): 405-8, 2001.,http://www.ncbi.nlm.nih.gov/sites/entrez.
2.) National Academy Press: A Genetic Study on the Children of Atomic Bomb Survivors, Washington, D.C., 1991 http://www.nap.edu/openbook.php?record_id=1800&page=R1
References
1.) Castronovo, Frank P. Teratogen Update: Radiation and Chernobyl, Teratology 60:100–106 (1999), Department of Health Physics and Radiopharmacology, Brigham and Women’s Hospital, Harvard Medical School, http://teratology.org/updates/60pg100.pdf
2.) Center for Disease Control, Prenatal Radiation Exposure: A Fact Sheet for Physicians, May 10 2006, Retrieved September 30, 2007 from
http://www.bt.cdc.gov/radiation/prenatalphysician.asp
3.) English, Melissa Nuclear Safety and Security in Russia and the World: Chernobyl, April 20 2005, retrieved September 28, 2007 from
http://www-pub.naz.edu:9000/~menglis6/Chernobyl.htm
4.) Galloway, David. Pregnancy and Cancer Treatment Often Are Not Mutually Exclusive. OncoLog, January 2004.
5.) Gwyn K, Theriault R: Breast cancer during pregnancy. Oncology (Huntingt) 15 (1): 39-46; discussion 46, 49-51, 2001.
6.) Health Physics Society, Pregnancy and Radiation, September 21, 2007, Retrieved September 25, 2007 from
http://hps.org/publicinformation/ate/faqs/pregnancyandradiationexposure.html
7.) Lindsey Anhalt. (2000). The Atomic Bomb: A study of the Aftermath. Retrieved September 27, 2007, from
https://artsci.wustl.edu/~copeland/atomicbomb.html
8.) Rall, David P. Toxic Agent and Radiation Control: Meeting the 1990 Objectives for the Nation, Public Health Reports, November-December 1984, Vol. 99, No. 6
9.) Ratnapalan, Savithiri, Nicole Bona and Gideon Koren Ionizing Radiation during Pregnancy, July 2003, Retrieved September 25, 2007 from
http://www.cfpc.ca/cfp/2003/Jul/vol49-jul-clinical-1.asp
10.) Rodier, Patricia M. Vulnerable Periods and Processes during Central Nervous System Development, Department of Obstetrics and Gynecology, University of Rochester, Rochester, New York
11.) Wertelecki, W. M.D. Birth Defects and Ukraine, Copyright 1998 - 2007 I.B.I.S., retrieved September 30, 2007 from http://www.ibis-birthdefects.org/start/kievtxt.htm
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