Absence of harmful effects of magnetic resonance exposure at 1.5 T in utero during the third trimester of pregnancy: a follow-up study

Abstract

In this study the possible adverse effects of in utero exposure to magnetic resonance (MR) conditions at 1.5 Tesla were examined. Thirty-five children between 1 and 3 years of age, and nine children between 8 and 9 years of age, that were exposed to MR during the third trimester of pregnancy, were checked for possible adverse effects in a follow-up study. Data on pregnancy and birth, the results of a neurological examination at 3 months, their medical documentary with emphasis on eye and ear functioning, and a questionnaire answered by their mothers were collected and evaluated. In five children abnormal test results were observed, that had no relation to the MR exposure. No harmful effects of prenatal MR exposure in the third timester of pregnancy were detected in this study.

Introduction

Examination techniques based on the principles of magnetic resonance (MR) have the potential to become important diagnostic tools during pregnancy because of their noninvasive and nonionizing character. MR imaging (MRI) provides additional anatomical information to assess congenital anomalies of the fetus [1] and the placenta [2] in cases where sonography is not conclusive. Besides, MRI has several advantages in overcoming the difficulties that complicate prenatal ultrasound, such as maternal obesity and oligohydramnios. Also for maternal health problems during pregnancy, MRI seems to be the most suitable examination technique [3]. It is 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 that “MRI 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.” MR spectroscopy supplies biochemical information that might be helpful to diagnose inborn errors of metabolism and to determine changes in metabolism, e.g., due to hypoxia [4], [5]. Furthermore, functional MRI might be a powerful tool to investigate normal and pathological brain development [6].

Although MR does not involve exposure to ionizing radiation, its potential health risks deserve further study. MR uses three different kinds of electromagnetic fields: static, time varying, and radio frequent electromagnetic fields. Theoretically, potential adverse effects on the fetus of all these three fields, both individually and combined, are possible. Several safety studies on MR exposure have been conducted. A small number of studies in human fetuses using regular MR imaging protocols within the safety recommendations that were performed in the late gestation period have not revealed any harmful effects on the fetus [7], [8], [9]. Also, exposure to static magnetic fields up to 4.7 Tesla in early gestation seems to induce no risk increase for adverse reproductive outcomes [10]. In addition, in vitro studies on proliferating human cells showed no adverse effects of static and time-varying magnetic fields [11]. However, animal studies on the safety of fetal MR are not conclusive and sometimes conflicting. In experimental procedures, hazardous effects to the fetus of long-duration exposure to static magnetic fields [12], of repetitive [13] or prolonged exposure [14], [15] to all three magnetic fields, and of in utero exposure to a field of 4.7 Tesla [16] have been demonstrated. However, some of these studies were experimentally deficient from both the MR exposure standpoint and the design of the experiments. The areas of concern are a reduced intrauterine growth [14], [15], [16] and harmful effects on temperature-sensitive tissue, e.g., eye lens [17] and testes [16]. Besides, very little is known about the possible damaging effects of the exposure to the very loud noise produced by common MRI and T₂-weighted fast imaging techniques, e.g., echo planar imaging and half-Fourier acquisition single shot turbo spin-echo (HASTE).

In order to determine the safety of MR techniques during pregnancy, more data on follow-up studies need to be presented. The aim of this study was to evaluate possible harmful effects of MR exposure on the fetus to a strong magnetic field (1.5 T). A prospective follow-up was performed in a group of normal fetuses that underwent an MR examination during the third trimester of pregnancy. Complementary to a general follow-up, special notice was given to the areas of concern, as observed in animal studies, and to hearing.