Magnetic resonance (MR) imaging has been used to evaluate obstetrical, placental, and fetal abnormalities in pregnant patients for more than 30 years. MR imaging is recognized as a beneficial diagnostic tool and is utilized to assess a wide range of diseases and conditions that affect the pregnant patient as well as the fetus.
Initially, there were substantial technical problems with the use of MR imaging primarily due to image degradation from fetal motion. However, several technological improvements, including the development of high-performance gradient systems and rapid pulse sequences, have provided major advances especially useful for imaging the pregnant patient and the fetus. Thus, MR imaging examinations for obstetrical and fetal applications may now be accomplished routinely in the clinical setting.
PREGNANCY AND MR SAFETY
The use of diagnostic imaging is often required in pregnant patients. Thus, it is not surprising that the question of whether or not a patient should undergo an MR examination during pregnancy will often arise. Safety issues include possible bioeffects of the static magnetic field of the MR system, risks associated with exposure to the gradient magnetic fields, the potential adverse effects of radiofrequency (RF) energy, and possible adverse effects related to the combination of these three electromagnetic fields.
MR environment-related risks are difficult to assess for pregnant patients due to the number of possible permutations of the various factors that are present in this setting (e.g., differences in field strengths, pulse sequences, exposure times, etc.). This becomes even more complicated since new hardware and software is developed for MR systems on an on-going basis.
There have been a number of laboratory and clinical investigations conducted to determine the effects of using MR imaging during pregnancy. Most of the laboratory studies showed no evidence of injury or harm to the fetus, while a few studies reported adverse outcomes for laboratory animals. However, whether or not these findings can be extrapolated to human subjects is debatable.
By comparison, there have been studies performed in pregnant human subjects exposed to MR imaging or the MR environment. Each investigation reported no adverse outcomes for the subjects. For example, Baker, et al. (1994) reported no demonstrable increase in disease, disability, or hearing loss in 20 children examined in utero using echo-planar MRI for suspected fetal compromise. Myers, et al. (1998) reported no significant reduction in fetal growth vs. matched controls in 74 volunteer subjects exposed in utero to echo-planar MRI performed at 0.5-Tesla. A survey of reproductive health among 280 pregnant MR healthcare professionals performed by Kanal, et al. (1993) showed no substantial increase in common adverse reproductive outcomes. Choi, et al. (2015) reported on a series of 15 patients exposed to MRI during the first trimester. Patients were prospectively followed up until the completion of their pregnancy during which there were no abnormalities attributed to MRI. This study provided preliminary evidence regarding the safety of MRI in first-trimester pregnant women.
There has been on-going concern that acoustic noise associated with MRI may impact the fetus. Reeves, et al. (2010) conducted an investigation to establish whether fetal exposure to the operating noise of 1.5-T MR imaging causes cochlear injury and subsequent hearing loss in neonates. The findings in this study provided evidence that exposure of the fetus to 1.5-T MR imaging during the second and third trimesters is not associated with an increased risk of substantial neonatal hearing impairment. In another study, Strizek, et al. (2015) reported no adverse effects of exposure to 1.5-T MRI in utero on neonatal hearing function.
With regard to the publications to date, there are discrepancies with respect to the experimental findings of the effects of electromagnetic fields used for MR procedures and the pertinent safety aspects of pregnancy. These discrepancies may be explained by a variety of factors, including the differences in the scientific methodology used, the type of organism examined, and the variance in exposure duration, as well as the conditions of the exposure to the electromagnetic fields. Additional investigations are warranted before the risks associated with exposure to MR procedures can be absolutely known and properly characterized.
GUIDELINES FOR THE USE OF MR PROCEDURES IN PREGNANT PATIENTS
As stated in the Policies, Guidelines, and Recommendations for MR Imaging Safety and Patient Management issued by the Safety Committee of the Society for Magnetic Resonance Imaging in 1991, “MR imaging may be used in pregnant women if other nonionizing forms of diagnostic imaging are inadequate or if the examination provides important information that would otherwise require exposure to ionizing radiation (e.g., fluoroscopy, CT, etc.). Pregnant patients should be informed that, to date, there has been no indication that the use of clinical MR imaging during pregnancy has produced deleterious effects.” This policy has been adopted by the American College of Radiology and is considered to be the “standard of care” with respect to the use of MR procedures in pregnant patients. Importantly, this information applies to MR systems operating up to and including 3-Tesla regardless of the trimester.
Thus, MR procedures may be used in pregnant patients to address important clinical problems or to manage potential complications for the patient or fetus. The overall decision to utilize an MR procedure in a pregnant patient involves answering a series of important questions that will address risk versus benefit including, the following:
- Is sonography satisfactory for diagnosis?
- Is the MR procedure appropriate to address the clinical question?
- Is obstetrical intervention prior to the MR procedure a possibility? That is, is termination of pregnancy a consideration? Is early delivery a consideration?
With regard to the use of MR procedures in pregnant patients, this diagnostic technique should not be withheld for the following cases:
- Patients with active brain or spine signs and symptoms requiring imaging.
- Patients with cancer requiring imaging.
- Patients with chest, abdomen, and pelvic signs and symptoms of active disease when sonography is non-diagnostic.
- In specific cases of suspected fetal anomaly or complex fetal disorder.
Abdelazim IA, et al. Complementary roles of prenatal sonography and magnetic resonance imaging in diagnosis of fetal renal anomalies. Aust N Z J Obstet Gynaecol 2010;50:237-41.
ACR–SPR Practice Parameter for the Safe and Optimal Performance of Fetal Magnetic Resonance Imaging (MRI) Res. 13 – 2010, Amended 2014. American College of Radiology (acr.org), Reston, VA.
Ain DL, et al. Cardiovascular imaging and diagnostic procedures in pregnancy. Cardiol Clin 2012;30:331-41.
Baker PN, et al, A three-year follow-up of children imaged in utero with echo-planar magnetic resonance. Am J Obstet Gynecol 1994;170:32-33.
Baron KT, et al. Comparing the diagnostic performance of MRI versus CT in the evaluation of acute nontraumatic abdominal pain during pregnancy. Emerg Radiol 2012;19:519-25.
Beddy P, et al. Magnetic resonance imaging for the evaluation of acute abdominal pain in pregnancy. Semin Ultrasound CT MR 2010;31:433-41.
Benson RC, Colletti PM, Platt LD, et al. MR imaging of fetal anomalies. Am J Roentgenol 1991;156:1205-1207.
Blondiaux E, Garel C. Fetal cerebral imaging - ultrasound vs. MRI: An update. Acta Radiol 2013;54:1046-54.
Bouyssi-Kobar M, et al. Fetal magnetic resonance imaging: Exposure times and functional outcomes at preschool age. Pediatr Radiol 2015 [Epub ahead of print].
Brown CEL, Weinreb JC. Magnetic resonance imaging appearance of growth retardation in a twin pregnancy. Obstet Gynecol 1988;71:987.
Carnes KI, Magin RL. Effects of in utero exposure to 4.7 T MR imaging conditions on fetal growth and testicular development in the mouse. Magn Reson Imaging 1996;14:263.
Chen MM, et al. Guidelines for computed tomography and magnetic resonance imaging use during pregnancy and lactation. Obstet Gynecol 2008;112 (2 Pt 1):333-40.
Choi JS, et al. A case series of 15 women inadvertently exposed to magnetic resonance imaging in the first trimester of pregnancy. J Obstet Gynaecol 2015 [Epub ahead of print].
Ciet P, Litmanovich DE. MR safety issues particular to women. Magn Reson Imaging Clin N Am 2015;23:59-67.
Colletti PM. Computer-assisted imaging of the fetus with magnetic resonance imaging. Comput Med Imaging Graph 1996;20:491.
Colletti PM, Platt LD. When to use MRI in obstetrics. Diag Imaging 11, 84, 1989.
Colletti PM, Sylvestre PB. Magnetic resonance imaging in pregnancy. MRI Clin N Am 1994;2:291.
Derntl B, et al. Stress matters! Psychophysiological and emotional loadings of pregnant women undergoing fetal magnetic resonance imaging. BMC Pregnancy Childbirth 2015;15:25.
De Wilde JP, et al. A review of the current use of magnetic resonance imaging in pregnancy and safety implications for the fetus. Prog Biophys Mol Biol 2005;87:335-353.
Dinh DH, et al. The use of magnetic resonance imaging for the diagnosis of fetal intracranial anomalies. Child Nerv Syst 1990;6:212.
Dunn RS, Weiner SN. Antenatal diagnosis of sacrococcygeal teratoma facilitated by combined use of Doppler sonography and MR imaging. Am J Roentgenol 1991;156:1115.
Fitamorris-Glass R, Mattrey RF, Cantrell CJ. Magnetic resonance imaging as an adjunct to ultrasound in oligohydramnio. J Ultrasound Med 1989:8:159.
Fraser R. Magnetic resonance imaging of the fetus. Initial experience [letter]. Gynecol Obstet Invest 1990;29:255.
Garcia-Bournissen F, Shrim A, Koren G. Safety of gadolinium during pregnancy. Can Fam Physician 2006;52:309-10.
Gardens AS, et al. Fast-scan magnetic resonance imaging of fetal anomalies. Br J Obstet Gynecol 1991;98:1217-1222.
Habib VV, et al. Early indicators of cervical insufficiency assessed using magnetic resonance imaging of the cervix during pregnancy. J Matern Fetal Neonatal Med 2015;28;626-31.
Hand JW, et al. Prediction of specific absorption rate in mother and fetus associated with MRI examinations during pregnancy. Magn Reson Med 2006;55:883-893.
Hand JW, et al. Numerical study of RF exposure and the resulting temperature rise in the foetus during a magnetic resonance procedure. Phys Med Biol 2010;55:913-30.
Heinrichs WL, et al. Midgestational exposure of pregnant BALB/c mice to magnetic resonance imaging conditions. Magnetic Resonance Imaging 1988;6:305.
Hill MC, et al. Prenatal diagnosis of fetal anomalies using ultrasound and MRI. Radiol Clin North Am 1988;26:287-307.
Horvath L, Seeds JW. Temporary arrest of fetal movement with pancuronium bromide to enable antenatal magnetic resonance imaging of holosencephaly. Am J Roentgenol, 1989;6:418-420.
Huisman TA. Fetal magnetic resonance imaging. Semin Roentgenol 2008;43:314-36.
International Commission on Non-Ionizing Radiation Protection statement, medical magnetic resonance procedures: Protection of patients. Health Physics 2004;87:197-216.
Jackson HA, Panigrahy A. Fetal magnetic resonance imaging: The basics. Pediatr Ann 2008;37:388-93.
Junkermann H. Indications and contraindications for contrast-enhanced MRI and CT during pregnancy. Radiologe 2007;47:774-7.
Expert Panel on MR Safety, Kanal E, Barkovich AJ, Bell C, et al. ACR guidance document on MR safe practices: 2013. J Magn Reson Imag 2013;37:501-30.
Kanal E, Gillen J, Evans J, Savitz D, Shellock FG. Survey of reproductive health among female MR workers. Radiology 1993;187:395-399.
Kanal E, Shellock FG, Sonnenblick D. MRI clinical site safety: Phase I results and preliminary data. Magn Reson Imaging 1988:7, Suppl 1:106.
Kay HH, Herfkens RJ, Kay BK. Effect of magnetic resonance imaging on Xenopus laevis embryogenesis. Magn Reson Imaging 1988;6:501-6.
Kikuchi S, et al. Temperature elevation in the fetus from electromagnetic exposure during magnetic resonance imaging. Phys Med Biol 2010;55:2411-26.
Kok RD, et al. Absence of harmful effects of magnetic resonance exposure at 1.5 T in utero during the third trimester of pregnancy: A follow-up study. Magnetic Resonance Imaging 2004;22:851-4.
Krishnamurthy U, et al. MR imaging of the fetal brain at 1.5T and 3.0T field strengths: Comparing specific absorption rate (SAR) and image quality. J Perinat Med 2015;43:209-20.
Lee JW, et al. Genotoxic effects of 3 T magnetic resonance imaging in cultured human lymphocytes. Bioelectromagnetics 2011;32:535-42.
Leithner K, et al. Psychological reactions in women undergoing fetal magnetic resonance imaging. Obstet Gynecol 2008;111(2 Pt 1):396-402.
Lenke RR, et al. Use of pancuronium bromide to inhibit fetal movement during magnetic resonance imaging. J Reprod Med 34,315-317, 1989.
Levine D. Obstetric MRI. J Magn Reson Imag 2006;24:1-15.
Malko JA, et al. Search for influence of 1.5 T magnetic field on growth of yeast cells. Bioelectromagnetics 1987;15:495.
Manganaro L, et al. Magnetic resonance imaging of fetal heart: Anatomical and pathological findings. J Matern Fetal Neonatal Med 2014;27:1213-9.
Mansfield P, et al. Study of internal structure of the human fetus in utero at 0.5-T. Br J Radiol 1990;13:314-318.
Masselli G, et al. Acute abdominal and pelvic pain in pregnancy: MR imaging as a valuable adjunct to ultrasound? Abdom Imaging 2011;36:596-603.
McCarthy SM, et al. Uterine neoplasms: MR imaging. Radiology 1989:170:125.
McRobbie D, Foster MA. Pulsed magnetic field exposure during pregnancy and implications for NMR foetal imaging. A study with mice. Magn Reson Imaging 1985;3:231.
Myers C, et al. Failure to detect intrauterine growth restriction following in utero exposure to MRI. Br J Radiol 1998;71:549.
Murakami J, et al. Fetal developmet of mice following intrauterine exposure to a static magnetic field of 6.3-T. Magn Reson Imaging 1992;10:433.
Nara VR, et al. Effects of a 1.5T static magnetic field on spermatogenesis and embryogenesis in mice. Invest Radiology 1996;31:586.
Oto A. MR imaging evaluation of acute abdominal pain during pregnancy. Magnetic Resonance Imaging Clin N Am 2006;14:489-501.
Palacios-Jaraquemada JM, et al. MRI in the diagnosis and surgical management of abnormal placentation. Acta Obstet Gynecol Scand 2013;92:392-7.
Patenaude Y, et al. The use of magnetic resonance imaging in the obstetric patient. J Obstet Gynaecol Can 2014;36:349-55.
Reeves MJ, et al. Neonatal cochlear function: Measurement after exposure to acoustic noise during in utero MR imaging. Radiology 2010;257:802-809.
Renfroe S, et al. Role of serial MRI assessment in the management of an abdominal pregnancy. BMJ Case Rep 2013;bcr2013200495.
Ruckhäberle E, et al. In vivo intrauterine sound pressure and temperature measurements during magnetic resonance imaging (1.5 T) in pregnant ewes. Fetal Diagn Ther 2008;24:203-10.
Semere LG, et al. Neuroimaging in pregnancy: A review of clinical indications and obstetric outcomes. J Matern Fetal Neonatal Med 2013;26:1371-9.
Shellock FG, Crues JV. MR procedures: Biologic effects, safety, and patient care. Radiology 2004;232:635-652.
Shellock FG, Kanal E. Policies, guidelines, and recommendations for MR imaging safety and patient management. J Magn Reson Imaging 1991;1:97.
Shellock FG, Kanal E. Chapter 4, Magnetic resonance procedures and pregnancy. In, Magnetic Resonance Bioeffects, Safety, and Patient Management. Second Edition, Lippincott-Ravin, Philadelphia, New York, 1996, pp. 49.
Smith FW, et al. Nuclear magnetic resonance imaging – a new look at the fetus. Br J Gynaecol 1985;92:1024-1033.
Smith FW, Sutherland HW. Magnetic resonance imaging: The use of the inversion recovery sequence to display fetal morphology. Br J Radiol 1988;61:338-341.
Sohlberg S, et al. Placental perfusion in normal pregnancy and early and late preeclampsia: A magnetic resonance imaging study. Placenta 2014;35:202-6.
Stark DD, et al. Pelvimetry by magnetic resonance imaging. Am J Roentgenol 1985;144:947-950.
Strizek B, et al. Safety of MR imaging at 1.5 T in fetuses: A retrospective case-control study of birth weights and the effects of acoustic noise. Radiology 2015;275:530-7.
Takahashi K, et al. Establishing measurements of subcutaneous and visceral fat area ratio in the early second trimester by magnetic resonance imaging in obese pregnant women. J Obstet Gynaecol Res 2014;40:1304-7.
Tesky GC, et al. Survivability and long-term stress reactivity levels following repeated exposure to nuclear magnetic resonance imaging procedures in rats. Physiol Chem Phys Med NMR 1987;19:43.
Tirada N, et al. Imaging pregnant and lactating patients. Radiographics 2015;35:1751-65.
Tocchio S, et al. MRI evaluation and safety in the developing brain. Semin Perinatol 2015;39:73-104.
Tyndall DA. MRI effects on the teratogenicity of x-irradiation in the C57BL/6J mouse. Magn Reson Imaging 1990;8:423.
Tyndall RJ, Sulik KK. Effects of magnetic resonance imaging on eye development in the C57BL/6J mouse. Teratology 1991;43:263
Tyndall DA. MRI effects on craniofacial size and crown-rump length in C57BL/6J mice in 1.5T fields. Oral Surg Oral Med Oral Pathol 1993;76: 65.
Yip YP, et al. Effects of MR exposure at 1.5 T on early embryonic development of the chick. J Magn Reson Imaging 1994;4:742.
Yip YP, et al. Effects of MR exposure on axonal outgrowth in the sympathetic nervous system of the chick. J Magn Reson Imaging 1995;4:457.
Yip YP, et al. Effects of MR exposure on cell proliferation and migration of chick motor neurons. J Magn Reson Imaging 1994;4:799.
Vadeyar SH, et al. Effect of fetal magnetic resonance imaging on fetal heart rate patterns. Am J Obstet Gynecol 2000;182:666.
Webb JA, et al. Members of Contrast Media Safety Committee of European Society of Urogenital Radiology (ESUR). The use of iodinated and gadolinium contrast media during pregnancy and lactation. Eur Radiol 2005;15:1234-40.
Weinreb JC, et al. Pelvic masses in pregnant patients, MR and US imaging. Radiology 1986;159:717.
Weinreb JC, et al. Magnetic resonance imaging in obstetric diagnosis. Radiology 1985;154:157-161.
Wenstrom KD, et al. Magnetic resonance imaging of fetuses with intracranial defects. Obstet Gynecol 1991;77:529-532.
Wieseler KM, et al. Imaging in pregnant patients: Examination appropriateness. Radiographics 2010;30:1215-29.
Wilcox A, et al. Incidence of early loss of pregnancy. New Engl J Med 1988;319:189-194.
Williamson RA, et al. Magnetic resonance imaging of anomalous fetuses. Obstet Gynecol 1989;73:952-956.
Zahedi Y, et al. Impact of repetitive exposure to strong static magnetic fields on pregnancy and embryonic development of mice. J Magn Reson Imag 2014;39:691-9.
Zaun G, et al. Repetitive exposure of mice to strong static magnetic fields in utero does not impair fertility in adulthood but may affect placental weight of offspring. J Magn Reson Imaging 2014;39:683-90.