The exposure of a foetus to the radiations is referred as the prenatal radiation exposure. This occurs when the mother is exposed to external radiations and can affect the unborn baby. Unborn babies are less sensitive to the radiations like X-rays in medical imaging at some pregnancy stages; however, between the 8 to 12 weeks of gestation, foetuses become sensitive to the external radiation (Petersen et al., 2015). These consequences can result in severe deformities like stunted growth, abnormal brain function, cancer or other deformities due to X-rays during the medical imaging procedure. The radiation exposure to x-rays can increase the likelihood of a disease that can affect the child even after birth with long-term effects. The risk depends on the duration and amount of radiation that the unborn babies are exposed to. According to Centres for Disease Control and Prevention (CDC) the threshold amount of radiation for safe exposure is 500 for the x-ray or less than that. A dose higher than the threshold up to 5000 can increase the risk of cancer for the baby after birth by less than 2% than the average rate (D’Oria et al., 2015). Therefore, it depicts that radiation exposure effects on the unborn baby and have long-term health effects. The following discussion involves the concepts of microscopic description of energy deposition, development of ideas of energy deposition, energy deposition in matter by radiation and energy average that are involved in the radiation effects on unborn babies.
Effect of ionizing radiation on matter and deposition
X-rays used during the medical imaging for ultrasonography are electromagnetic radiations having wavelength shorter than UV rays and carries photons. These are highly energetic and possess enough energy to ionize the atoms leading to disruption of molecular bonds. This kind of ionizing radiation is harmful to the tissues and can cause radiation sickness that can induce cancer and long-term disability on the unborn baby. In the medical imaging process, X-rays can increase the cause of cancer that outweighs the examination benefits during the pregnancy (Matsunaga et al., 2017). This is the reason that x-rays ionizing capability is used for the cancer treatment and kill the cancer cells through the radiation therapy. The effect of ionizing radiation on matter and deposition that is living tissue is more likely to be closely related to the amount of the energy that is deposited on them during the exposure rather than radiation charge. This is the absorbed dose that can get deposited on the mother’s body affecting the foetus. This is the unit measurement of the amount of radiation required that can cause deposition of one joule of energy in one kilogram on any matter like on the living tissue. This can cause deposition on the mother’s tissue and affect the unborn foetus during the medical imaging procedure. This energy deposition of matter on foetus during the organ formation can have detrimental effects on the foetus. There might be developmental defects in the developing foetus like reduced diameter of head or mental retardation between the 8 to 15 weeks after conception (Kamiya et al., 2015).
High doses of this energy deposition in joules/kilogram on the living tissue can cause gross malformation or death. The threshold effect is between the 0.1 Sv and 1 Sv depending on time of conception. Genetic risks can also be there in foetuses after birth. Moreover, irradiation before the birth can also cause malignancy during childhood and overall risk for cancer doubles. Therefore, it is advisable for the pregnant mothers to avoid the medical imaging procedure until necessary, in cases of delay until attainment of pregnancy is advisable. There is also effect of deposition of matter on the mother tissue especially in mothers who are employed in radiation sources and can affect the unborn baby (Brent, Beckman & Jensh, 2013).
This high deposition of energy in matter can affect the unborn child between the 2 to 18 weeks of pregnancy. During this time, the exposure to harmful x-ray radiations used in medical imaging can cause severe birth defects like brain damage. This deposition of matter on the living tissue during exposure goes into the bloodstream of the mother and can cross the umbilical cord reaching the foetus and cause birth anomalies (Sherer et al., 2014). The frequency of radiation exposure is maximum during the first few weeks of pregnancy and can cause all-or-none effect on the embryo during the first week following conception. Foetal dose estimation is done with the experts of the radiation dosimetry about the radiation dose estimation during the foetal exposure to x-rays in medical imaging. The ionization radiation and its energy deposition in matter can impair the crucial foetal development. There can be growth retardation and severe birth defects in the unborn foetus when the energy deposition in matter is more than threshold amount (Ray et al., 2016).
Effect of Magnetic Resonance Imaging
Magnetic resonance imaging has been identified with many risks due to application during pregnancy. There has been a review on the risks of the growing foetus while considering the hazards of the static magnetic field of MRI. The risks arise due to the time-varying magnetic field and pulsed radio frequency fields. The effects will include the following damages, biological anomalies in the development of the foetus, miscarriages. A research based survey was carried on based on the maternal MRI diagnosis, the state of foetus and the work practices. The results showed that about 91% of pregnant women are in need of the MRI based diagnosis in the first and third trimester (Patenaude et al, 2014). There has been found occurrence of miscarriage with the application of the magnetic field resonance. MR1 often affects at the cellular level due to the induction of the local electric fields, static currents and the heating of the radiofrequency fields.
The medical imaging procedures like the CT, PET and SPECT are involving the use of the ionization radiation. However, such radiation based imaging techniques are extensively required for accurate diagnosis (Stabin, 2017). It has been reported that due to high radio-sensitivity of the embryo, there are possible concerns of radiation-induced cancers due to exposure on the pregnant females. Thus it is required to maintain a correct doe estimation and subjection at the organ level from the nuclear medical process. In this literature, they have produced a series of computational pregnant female phantoms to identify the required doses that will confirm the safety of use in the females. The dosimetry calculations were done by using the Monte Carlo simulations that gave the estimate on the absorbed doses. It has also been identified that major foetal risks are associated with the F-18 radiotracers. The estimated absorbed dose tolerable was found to be around 0.021 mGy/MBq (Xie & Zaidi, 2015).
There require a correct estimation of the absorbed dose especially while restaging or diagnosing by using PET, positron emission tomography. There has been high sensitivity with the damaging ions on the foetus and the pregnant women. The correct doses are highly required while subjecting women to radiotracers. Wide area of research has been made to calculate the safety limits of the radiation doses tolerable to the foetus. There has been creation of hypothetical models of computational phantoms of pregnant female models. It has been found that if the doses are not given in the safety limits then the ionisation energy that when strikes the uterine tissue can be teratogenic, mutagenic (Vano, 2015). The foetal organogenesis gets affected with the susceptibility of the exposure to the ionisation radiations from the radionucleides of the PET imaging technique. Mainly cases like the spontaneous abortion, retardation in growth and mental health developments get affected in the unborn babies. Before exposure of the radiations to the pregnant women, the total foetal radiation absorbed dose must be maintained and the mother should be counselled about the risks that are potentially associated (Kelaranta et al, 2015).
Effect of scattered radiation exposure and risks
Study has highlighted on the need for diagnostic or interventional X-ray examination. Conceptus dose estimation has been identified as the preferred method for evaluating the radiogenic risks for the unborn child. Scattered radiation exposure to the foetus is common under such circumstances when extra-abdominal examination is carried out at dose lower than 1 mGy. Pelvis X-ray amounts to higher dose of radiation exposure and is associated to foetus dose of 10-25 mGy. A threshold of less than 100 mGY has been identified as not threatening and does not essentially lead to therapeutic abortion. Utilization of suitable conversion coefficients as laid down by international organizations has been considered crucial for assessment of radiation dose that might pose threat for stochastic effects to the embryo. Thus, it has been suggested to use the CODE (COnceptus Dose Estimation), free web-based software for the sake of estimating the conceptus radiation dose risks in case of pregnancy (Damilakis, 2016). Another study has focused on evidence based recommendations pertinent to diagnostic radiation exposure during pregnancy. Mental and growth deficiency alongside increased risk of microcephaly has been attributed to antenatal exposures to high doses of radiation in the range of 50 rad. Further an inverse association has been established with respect to gestational age and radiation exposure whereby highest reported rates of foetal anomalies are found due to risk at the 8-15 weeks of gestation. Adverse pregnancy outcomes are evident in cases of higher radiation dosing that in turn aggravates the risk of teratogenicity apart from induction of childhood malignancies and hematologic disorders. Emphasis has been laid on knowledge of the clinicians about the use of iodine-based contrast material in case of contrast-enhanced mammography and CT mammography as opposed to utilization of gadolinium in MRI to allay the potential risks (Rimawi, Green & Lindsay, 2016).
Research carried out with respect to assessment of radiation exposure risks in case of pregnant patient who are subjected to Percutaneous Nephrostomy (PCN) Tube Placement procedure has laid impetus on the discrete roles of the healthcare professionals who are engaged in caring for the concerned client. Data suggests that prenatal radiation exposure of greater than 50 rad is likely to harbor estimated childhood cancer incidence amounting to greater than 6%. Lifetime cancer risk of greater than 55% has been reported at such scenarios. Thorough evaluation of the patient in the definite gestational period necessitates the need for maintaining proper procedural care by the concerned ionizing radiation (IR) team professionals. PCN being a low volume, high-risk operation, poses threat for far reaching implications due to radiation exposure, to ensure provision of optimal care facility to the patient (Sharma et al., 2016). An interesting study reported the foetal dose results at the time of CyberKnife radiosurgery for a brain tumor in pregnancy. Findings derived from the study revealed that the average dose to the foetus was 4.2 cGy as measured through Farmer chamber and EBT3 films. It was further concluded from the stud that preceding the normal incidence, the radiogenic cancer risk is <0.3%. However the measured foetal doses were found to lie below the threshold of 10 cGy that account for congenital malformations, mental and growth retardation effects thereby indicating the safe administration of the treatment modality to allow the patient to deliver a healthy child. The safe mode of utilization of the CyberKnife radiosurgery for a brain tumor in pregnancy has thus been elucidated through these vital findings (Pantelis et al., 2016).
Study has paid attention to the use of molecular imaging techniques such as PET and hybrid modalities such as PET/CT and PET/MRI as an indispensable tool in case of oncologic malignancies. Considering the wide spectrum application of these novel technologies and presentation of high sensitivity of the developing foetus to the ionizing radiation, it has been suggested crucial to evaluate potential radiation risks through estimation of the radiation dose delivered to foetus and pregnant patients. In order to cater to these objectives, eight embryo models at various gestational periods having 25 recognized issues as per the reference data suggested by the ICRP was constructed. Both internal as well as external dose calculations were calculated by virtue of dedicated software packages. The study results indicated the usability and credibility of S-values for standardization of the dose estimates in pregnant patients and foetus obtainable from a varied range of positron-emitting labelled radiotracers amongst other available computational values such as that of Monte Carlo calculations, effective dose and organ absorbed dose (Xie & Zaidi, 2016). Further well-defined guidelines has been put forward for the coordinated radiologist/gynecologist-obstetrician for foetal MRI or CT. Thorax, abdomen and central nervous system are the commonest seats of MRI investigations in the foetus while potential skeletal abnormalities are detected by mean of CT. Diagnostic ultrasound examinations are also employed by the dedicated teams of professionals for screening of potential issues. Research has generated to adverse data related to the negative influences of strong magnetic fields in the range of 1.5 Tesla to even 3 Tesla, but it has been suggested that both medical as well as paramedical staff must be well informed and aware about the consequences of such applications. Optimization of the radiation dose is further suggested to minimize foetal exposure and enhance the quality of imaging procured due to such intervention (Meder et al., 2017).
Effects of prenatal radiation
Recent evidences for structural, developmental and functional brain defects following exposure to prenatal radiation has been explicitly discussed in study. In recent years, medical imaging has gained considerable prominence owing to its wide array of applicability to the diagnosis of medical conditions. The risks associated with cumulative response to low radiation exposure such as that of CT has garnered considerable attention although specific values for safety have not been established yet to emphatically indicate the no-hazardous mode associated with these imaging techniques. Radiation exposure to the pregnant mother is likely to pose some threat to the unborn child due to the ionizing nature of such radiations that might be detrimental to the health of the child. in utero radiation exposure has been referred to in the study for understanding the link between persistent anomalies and early defects following exposure to a certain radiation threshold. Radiation therapies including chest and abdominal radiography, CT and breast cancer radiotherapy has been explored for their individual mean foetal doses. Acknowledgment of such conditions will help to harbor better health outcomes for the pregnant mothers as well as their unborn children through importance being laid onto the protection from radiation hazards (Verreet et al., 2016). Another follow up study focused on the foetal CT radiation dose for the sake of establishing the diagnostic reference level (DRL). The parameters related to volume CT dose index (CTDIvol), dose-length product (DLP) revealed that in contrast to the study conducted in year 2011, the minimum, 5th percentile, median, and 75th percentile values diminished as per results tabulated in year 2015 from the allocated sites. Thus the DRL was found to be decreased on follow-up thereby adding to the efficacy of the imaging done (Miyazaki et al., 2017).
Effect of Endoscopic retrograde cholangio-pancreatography (ERCP)
Empirical research attended to the use of Endoscopic retrograde cholangio-pancreatography (ERCP) as a therapeutic tool to manage bilio-pancreatic diseases. Risks in case of both the mother and foetus have been indicated due to such interventions under the effect of exposures to ionizing radiations. Death of the foetus, retardation of growth, malformations, microcephaly, mental retardation and potential heightened risk to childhood cancer has been indicated. Long-term follow up report for babies following ERCP intervention has been reported. The study outcomes pacified the risk due to ERCP as no long-term hazardous consequences was not significant. Neurological maturation and growth development all followed a normal discourse. Further no childhood cancer was reported in the studied population. Thus, the safe and effectiveness of ERCP was confirmed through the study results (Laudanno et al., 2016). Another pertinent study explored the issue relevant to the known low as well as high dose ionizing radiation exposure during pregnancy in humans. The study indicated on the consensus reached regarding the increased incidence of microcephaly together with the decreased IQ in the atomic bomb survivors while there is no definite documentation or explanation with respect to increased risk of cancer for diagnostic radiography. The study findings has harped on considering the long term effects of prenatal radiation exposure for assessment of radiation risk because of the fact that these effects hold true even in the low doses. The trends across developmental stages encompassing pre-implantation, organogenesis and foetal development need to be evaluated to accurately investigate the potential impacts of the ionizing radiations in the unborn child (Sreetharan et al., 2017).
Effect of low dose ionizing radiation (LDIR)
The rise in the applications of medical imaging that essentially resort to ionizing radiations have increased the exposure to low dose ionizing radiation (LDIR) in patients. The detrimental outcomes following the high dose ionizing radiations have already been established through suitable researches. Reports have unravelled that LDIR is capable of causing oxidative stress that might not essentially result in genomic mutations but do pose certain health risks due to exposure. Epigenetic mechanisms are triggered due to oxidative stress that leads to heritable modifications in the cells of the organisms. Permanent cellular transformations follow these epigenetic modifications that might not cause significant alteration in the underlying DNA nucleotide sequence. Thus, the outcomes of the research findings are indicative of the presence of a mechanistic link between the LDIR and epigenetic gene modulation. Thus during pregnancy, heightened susceptibility is observed in case of intrauterine foetal development following oxidative stress induced epigenetic programming (Tharmalingam et al., 2017). Another study by means of referring to animal data through 18F-FDG injection in pregnant women leads to the derivation of the standard values of foetal dosimetry. The observed time integrated activity coefficients coupled with a new generation of anthropometric voxel based pregnancy phantoms culminated in the estimation of the final doses that are suitable for application. Thus, the updated foetal doses has been recommended to be 2.6 E-02 mGy/MBq for early pregnancy condition, 1.9 E-02 mGy/MBq at 3 months gestation, 1.4 E-02 mGy/MBq at 6 months gestation and finally 6.9 E-02 mGy/MBq at 9 months gestation (Zanotti-Fregonara & Stabin, 2017).
Supportive literatures with respect to the studies published concerning the theme of the effects of radiation exposure in unborn babies thus may be referred to for gaining a proper insight into the topic of investigation that hold relevance in clinical terms to safeguard the lives of both the pregnant mother as well as their foetus.
Brent, R. L., Beckman, D. A., & Jensh, R. P. (2013). Relative radiosensitivity of fetal tissues. Relative Radiation Sensitivities of Human Organ Systems, 12, 239-256.
D’Oria, L., Pellegrino, M., Licameli, A., De Luca, C., Visconti, D., Donati, L., ... & De Santis, M. (2015). Prenatal X-ray Exposure and Teratogenic Risks: A literature Review. Razavi International Journal of Medicine, 3(2).
Damilakis, J. (2016). Unborn children: Radiation protection in pregnancy. Physica Medica: European Journal of Medical Physics, 32, 182.
Kamiya, K., Ozasa, K., Akiba, S., Niwa, O., Kodama, K., Takamura, N., ... & Wakeford, R. (2015). Long-term effects of radiation exposure on health. The Lancet, 386(9992), 469-478.
Kelaranta, A., Kaasalainen, T., Seuri, R., Toroi, P., & Kortesniemi, M. (2015). Fetal radiation dose in computed tomography. Radiation protection dosimetry, 165(1-4), 226-230.
Laudanno, O. M., Gollo, P., Ahumaran, G., Lasagna, R., & Bravo, J. (2016). 343 Fetal radiation exposure during ERCP: Long term follow up. Gastrointestinal Endoscopy, 83(5), AB140.
Matsunaga, Y., Kawaguchi, A., Kobayashi, M., Suzuki, S., Suzuki, S., & Chida, K. (2017). Radiation doses for pregnant women in the late pregnancy undergoing fetal-computed tomography: a comparison of dosimetry and Monte Carlo simulations. Radiological physics and technology, 10(2), 148-154.
Meder, J. F., le Pointe, H. D., H?don, B., & Benachi, A. (2017). Guidelines for coordinated radiologist/gynecologist-obstetrician management of patients requiring fetal MRI or CT.
Miyazaki, O., Sawai, H., Yamada, T., Murotsuki, J., & Nishimura, G. (2017). Follow-Up Study on Fetal CT Radiation Dose in Japan: Validating the Decrease in Radiation Dose. American Journal of Roentgenology, 208(4), 862-867.
Pantelis, E., Antypas, C., Frassanito, M. C., Sideri, L., Salvara, K., Lekas, L., ... & Romanelli, P. (2016). Radiation dose to the fetus during CyberKnife radiosurgery for a brain tumor in pregnancy. Physica Medica, 32(1), 237-241.
Patenaude, Y., Pugash, D., Lim, K., Morin, L., Bly, S., Butt, K., ... & Naud, K. (2014). The use of magnetic resonance imaging in the obstetric patient. Journal of Obstetrics and Gynaecology Canada, 36(4), 349-355.
Petersen, I., McCrea, R. L., Lupattelli, A., & Nordeng, H. (2015). Women9s perception of risks of adverse fetal pregnancy outcomes: a large-scale multinational survey. BMJ open, 5(6), e007390.
Ray, J. G., Vermeulen, M. J., Bharatha, A., Montanera, W. J., & Park, A. L. (2016). Association between MRI exposure during pregnancy and fetal and childhood outcomes. Jama, 316(9), 952-961.
Rimawi, B. H., Green, V., & Lindsay, M. (2016). Fetal implications of diagnostic radiation exposure during pregnancy: evidence-based recommendations. Clinical obstetrics and gynecology, 59(2), 412-418.
Sharma, A. K., Mis, F. J., Vo, T. D., & Grossman, V. G. A. (2016). Percutaneous Nephrostomy Tube Placement in Pregnancy: Care of the Mother and Unborn Child. Journal of Radiology Nursing, 35(2), 85-96.
Sherer, M. A. S., Visconti, P. J., Ritenour, E. R., & Haynes, K. (2014). Radiation Protection in Medical Radiography-E-Book. Elsevier Health Sciences.
Sreetharan, S., Thome, C., Tharmalingam, S., Jones, D. E., Kulesza, A. V., Khaper, N., ... & Tai, T. C. (2017). Ionizing Radiation Exposure During Pregnancy: Effects on Postnatal Development and Life. Radiation Research, 187(6), 647-658.
Stabin, M. G. (2017). Radiation Dosimetry of PET Imaging. In Basic Science of PET Imaging (pp. 65-76). Springer International Publishing.
Tharmalingam, S., Sreetharan, S., Kulesza, A. V., Boreham, D. R., & Tai, T. C. (2017). Low-Dose Ionizing Radiation Exposure, Oxidative Stress and Epigenetic Programing of Health and Disease. Radiation Research.
Vano, E. (2015). Basis for standards: ICRP activities. Radiation protection dosimetry, 165(1-4), 30-33.
Verreet, T., Verslegers, M., Quintens, R., Baatout, S., & Benotmane, M. A. (2016). Current Evidence for Developmental, Structural, and Functional Brain Defects following Prenatal Radiation Exposure. Neural plasticity, 2016.
Xie, T., & Zaidi, H. (2015, July). Construction of pregnant female phantoms at different gestation periods for radiation dosimetry. In Proc of the 5th International Workshop on Computational Phantoms for Radiation Protection, Imaging and Radiotherapy. Seoul, Korea (pp. 19-22).
Xie, T., & Zaidi, H. (2016). Development of computational pregnant female and fetus models and assessment of radiation dose from positron-emitting tracers. European journal of nuclear medicine and molecular imaging, 43(13), 2290-2300.
Zanotti-Fregonara, P., & Stabin, M. G. (2017). New Fetal Radiation Doses for 18F-FDG Based on Human Data. Journal of Nuclear Medicine, jnumed-117.