Monday, March 05, 2007

Pregnant healthcare workers and MRI/NMR Magnetic Resonance

Pregnancy, Health care workers and Magnetic Resonance (NMR/MRI)

E. Kanal


A pregnant researcher wants to know if it is safe to work with an MRI. What do I tell her?

Pregnancy and MR can be an issue from the point of view of the pregnant patient or the health care practitioner.

The Pregnant Patient and MR
There is no reproducible data available to date to my knowledge that demonstrates deleterious, or harmful effects of undergoing an MR examination as a pregnant patient (either to the developing fetus or the pregnant patient herself). Nevertheless, in a 1988 survey we performed we were surprised to see that a full 36% of all sites that responded to this particular questions stated that they unequivocally did not scan pregnant patients. In the University of Pittsburgh Medical Center our practice regarding pregnant patients is as follows: If the study being requested has the potential to change/affect the care of that patient (and/or fetus) DURING that same pregnancy, and if there are no other non-ionizing examinations that can provide the same diagnostic information, and if the examination itself cannot wait until the termination of that pregnancy, we will scan such patients regardless of which trimester the patient is in.
The only hesitation that should be added here pertains to the usage of gadolinium-based MR contrast agents. It is known that Magnevist (and presumably the other presently FDA-approved intravenous MR contrast agents of Omniscan and ProHance) readily crosses the placental “barrier” and can be found in fetal baboon bladders in just a few minutes after injection into the maternal peripheral circulation. The fetus will then excrete this urine/contrast mixture into the amniotic fluid, swallow it, etc. in the typical amniotic fluid cycle. There does not seem to be any data available to date to suggest what the clearance rate of this gadolinium complex might be from the amniotic fluid. Although there is good data demonstrating that absorption of these gadolinium complexes via the gastrointestinal tract in adults is near zero, it is unclear if this also applies to a) the developing GI tract of a fetus, and b) free gadolinium that may form, or dissociate from its chelating molecule. What is know, however, is that the longer the gadolinium complex stays in the body the greater the amount that may be released as the potentially harmful free gadolinium ion.
Thus, it may well be prudent to avoid administering gadolinium chelates to pregnant patients that are cleared to undergo an MR examination. To my knowledge, although we have studied scores of pregnant patients with MR during their pregnancies, we have never, to my knowledge, knowingly administered a gadolinium chelate to a pregnant patient. While it may one day, in a particular clinical circumstance, be clinically advisable to do so from a risk-benefit point of view, I simply have not yet had the opportunity to personally come across such a circumstance, and have avoided administering these gadolinium-based MR contrast agents to pregnant patients to date.

The Pregnant Health Care Practitioner and MR
This issue is somewhat more complicated from a medicolegal point of view. After all, the concept of risk-benefit ratio may not be as applicable here, since the individual with the benefit (presumably the technologist, nurse, physicist, physician, etc. employed to work in the MR environment) is not necessarily the same, or only one, undergoing the potential risks (i.e., the fetus).
In an attempt to assess this question, we reviewed the literature to see what was known regarding longer term exposures to such time varying and/or constant (a.k.a., static) magnetic fields. We also sent out a survey to all female MR technologists and nurses in the USA that we were able to identify in 1990/1991 and asked numerous questions (it was an eight page questionnaire) regarding predominantly female reproductive health care issues. We distributed questionnaires to 2000 sites and included 3 to 4 copies of the questionnaire in each mailing, requesting from the site administrator that they distribute the questionnaire to all female MR technologists and nurses.
We received 1915 responses (9% from nurses, 91% from technologists). The survey results included a total of 1421 pregnancies, of which 280 occurred while working as an MR employee (technologist or nurse), 894 while employed at another job, 54 as a student and 193 while homemakers. The data regarding pregnancy outcomes for this population was analyzed for numerous factors and compared to pregnancy outcomes of the same population when they were employed elsewhere, prior to working in the MR environment. Among the factors studied were the pregnancy outcome, fertility, length of gestational period, gender of the offspring, and birth weight. These factors (among others) were compared to the incidences and rates for these categories among the same group when they were employed elsewhere, prior to their working in the MR environment. The data was also corrected for three well known potential confounders: smoking during pregnancy, alcohol use during pregnancy, and maternal age greater than 30 years old at time of delivery.
The data analysis failed to reveal any statistically significant associations between any of these categories and working as an MR health care provider. In other words, there was no statistically significant difference between the rates of spontaneous abortions/miscarriages, or low birth weights, or premature delivery, or infertility, or male offspring between those working as MR employees versus the same population when they were employed elsewhere, prior to working as an MR health care provider.
As a result of these investigations, we decided at the University of Pittsburgh Medical Center to permit the pregnant health care provider to scan, position, archive, film, inject contrast, respond to emergent patient needs, etc. for patients undergoing MR examinations in any of our five 1.5 Tesla clinical MR scanners.
The only restriction we requested was that the pregnant health care provider not remain in the magnet room with the patient during scanning itself. (In actuality, the potential concern is that they not remain in the bore of the imaging system itself during scanning, but to avoid confusion we simplified it by asking them to remain out of the magnet room itself in which imaging is occurring during scanning.) The reason for this is NOT that we believe, or have found, that this might prove harmful to the employee or her fetus, but rather that it is my opinion that there is as of yet insufficient data to demonstrate that this would be a low risk practice. Specifically, data regarding longer term exposure to the time durations and patterns and strengths of the time varying (electric and) magnetic fields active in the bore of an MR imaging system during scanning are sparse at best. Thus, it is not that such exposure would necessarily be harmful, but rather that I am not personally comfortable stating at this time that it would more likely than not be safe to do so. As more data become available, this recommendation is certainly subject to review and modification. At this time the only practical outcome of this recommendation limitation is that pregnant nurse practitioners are advised/requested not to be the ones designated to accompany a neonate, for example, into the bore of an MR scanner during imaging to manually ventilate the patient, etc.

Take home
I permit pregnant health care providers to perform all functions and duties normally associated with their jobs during pregnancy, with the only exception being that I request that they not remain within the scan room with the patient during the actual imaging itself.

Kanal E, Gillen J, Evans JA, Savitz DA, Shellock FG.
Survey of reproductive health among female MR workers.
Radiology, 1993: 187: 395-399.

There are also other references that you can find in this article that may prove useful in your research of this topic.



Anonymous said...

If you continue to smoke throughout your pregnancy, you risk harming the child in your womb. Before you became pregnant, you were only harming yourself, but now you’re responsible for the life growing inside you too. If you smoke during pregnancy, you are more likely to birth a child who is underweight.

Cricket said...

In looking at this data it appears that only 280 pregnancies were actually conceived or took place during exposure to MRI. Is this correct? If so, this is a very small sample size and might require further investigation.

Molly Marando said...

My problem with these research studies is that there is no mention of what job duties the pregnant technologists were fulfilling when participating in the study. It was common practice at that time for the techs to stay out of the room.