Download Guidelines for Diagnostic Imaging During Pregnancy

ACOG
Committee on
Obstetric Practice
Committee
Opinion
Number 299, September 2004
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Guidelines for diagnostic imaging
during pregnancy. ACOG Committee
Opinion No. 299. American College
of Obstetricians and Gynecologists.
Obstet Gynecol 2004;104:647–51.
VOL. 104, NO. 3, SEPTEMBER 2004
(Replaces No. 158, September 1995)
Guidelines for Diagnostic Imaging
During Pregnancy
ABSTRACT: Undergoing a single diagnostic X-ray procedure does not result
in radiation exposure adequate to threaten the well-being of the developing
preembryo, embryo, or fetus and is not an indication for therapeutic abortion.
When multiple diagnostic X-rays are anticipated during pregnancy, imaging
procedures not associated with ionizing radiation, such as ultrasonography
and magnetic resonance imaging, should be considered. Additionally, it may
be helpful to consult an expert in dosimetry calculation to determine estimated fetal dose. The use of radioactive isotopes of iodine is contraindicated for
therapeutic use during pregnancy. Other radiopaque and paramagnetic contrast agents have not been studied in humans, but animal studies suggest that
these agents are unlikely to cause harm to the developing human fetus.
Although imaging techniques requiring these agents may be diagnostically
beneficial, these techniques should be used during pregnancy only if potential
benefits justify potential risks to the fetus.
Various imaging modalities are available for diagnostic use during pregnancy. These include X-ray, ultrasonography, magnetic resonance imaging
(MRI), and nuclear medicine studies. Of these, diagnostic X-ray is the most
frequent cause of anxiety for obstetricians and patients. Much of this anxiety
is secondary to a general belief that any radiation exposure is harmful and
will result in an anomalous fetus. This anxiety could lead to inappropriate
therapeutic abortion and litigation. Actually, most diagnostic radiologic procedures are associated with little, if any, known significant fetal risks.
Moreover, according to the American College of Radiology, no single diagnostic X-ray procedure results in radiation exposure to a degree that would
threaten the well-being of the developing preembryo, embryo, or fetus (1).
Thus, exposure to a single X-ray during pregnancy is not an indication for
therapeutic abortion (2, 3).
Some women are exposed to X-rays before the diagnosis of pregnancy.
Occasionally, X-ray procedures will be indicated during pregnancy for significant medical problems or trauma. To enable physicians to counsel patients
appropriately, the following information is provided about the potential risks
and measures that can reduce diagnostic X-ray exposure.
ACOG Committee Opinion No. 299 Guidelines for Diagnostic Imaging
During Pregnancy
647
X-Ray Exposure
Ionizing radiation can result in the following 3 harmful effects: 1) cell death and teratogenic effects, 2)
carcinogenesis, and 3) genetic effects or mutations
in germ cells (2, 3). There is little or no information
to estimate either the frequency or magnitude of
adverse genetic effects on future generations.
Units traditionally used to measure the effects of
X-ray include the rad and roentgen equivalents man
(rem). Modern units include the gray (Gy) and sievert (Sv). The definitions of these units of measure
are summarized in Table 1.
The estimated fetal exposure from some common radiologic procedures is summarized in Table
2. A plain X-ray generally exposes the fetus to very
small amounts of radiation. Commonly during pregnancy, the uterus is shielded for nonpelvic procedures. With the exception of barium enema or small
bowel series, most fluoroscopic examinations result
in fetal exposure of millirads. Radiation exposure
from computed tomography (CT) varies depending
on the number and spacing of adjacent image sections. Although CT pelvimetry can result in fetal
exposures as high as 1.5 rad, exposure can be
reduced to approximately 250 mrad (including fetal
gonad exposure) by using a low-exposure technique
(4).
Spiral (or helical) CT allows continuous scanning of the patient as the couch is moved through the
scanner, providing superior speed and image quality.
Radiation exposure is affected by slice thickness, the
number of cuts obtained, and the “pitch,” a ratio
defined as the distance the couch travels during one
360-degree rotation divided by the section thickness.
The patient dose is proportional to 1 per pitch.
Under typical use with a pitch of 1 or greater, the
radiation exposure to the fetus from spiral CT is
comparable to conventional CT (5).
Cell Death and Teratogenic Effects
Data from an animal study suggest that exposure to
high-dose ionizing radiation (ie, much greater than
that used in diagnostic procedures) before implantation will most likely be lethal to the embryo (2). In
other words, cell death is most likely an “all or
none” phenomenon in early embryonic development.
Myriad teratogenic effects have developed in
animals exposed to large doses of radiation (ie,
100–200 rad). However, in humans, growth restriction, microcephaly, and mental retardation are the
most common adverse effects from high-dose radiation (3, 6, 7). Based on data from atomic bomb survivors, it appears that the risk of central nervous
system effects is greatest with exposure at 8–15
weeks of gestation, with no proven risk at less than
8 weeks of gestation or at greater than 25 weeks of
gestation (3, 8). Thus, at 8–15 weeks of gestation,
the fetus is at greatest risk for radiation-induced
mental retardation, and the risk appears to be a “nonthreshold linear function of dose” at doses of at least
20 rad (3, 6, 8, 9). For example, the risk of severe
mental retardation in fetuses exposed to ionizing
radiation is approximately 40% at 100 rad of exposure and as high as 60% at 150 rad of exposure (3,
8). It has been suggested that a threshold for this
adverse effect may exist in the range of 20–40 rad
(7, 8). Even multiple diagnostic X-ray procedures
rarely result in ionizing radiation exposure to this
degree. Fetal risks of anomalies, growth restriction,
or abortions are not increased with radiation exposure of less than 5 rad, a level above the range of
exposure for diagnostic procedures (2).
Carcinogenesis
The risk of carcinogenesis as a result of in utero
exposure to ionizing radiation is unclear but is prob-
Table 1. Some Measures of Ionizing Radiation
Measure
Definition
Unit
Exposure
Dose
Number of ions produced by X-rays per kilogram of air
Amount of energy deposited per kilogram of tissue
Roentgen (R)
Rad (rad)*
Relative
effective
dose
Amount of energy deposited per kilogram of tissue
normalized for biological effectiveness
Roentgen
equivalents
man (rem)*
Unit
Roentgen (R)
Gray (Gy)
1 Gy = 100 rad
Sievert (Sv)
1 Sv = 100 rem
*For diagnostic X-rays, 1 rad = 1 rem
Cunningham FG, Gant NF, Leveno KJ, Gilstrap LC 3rd, Hauth JC, Wenstrom KD. General considerations and maternal evaluation. In: Williams obstetrics. 21st ed. New York (NY): McGraw-Hill; 2001. p. 1143–58. Reproduced with permission of The McGraw-Hill Companies.
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OBSTETRICS & GYNECOLOGY
Table 2. Estimated Fetal Exposure From Some Common
Radiologic Procedures
Procedure
Fetal Exposure
Chest X-ray (2 views)
Abdominal film (single view)
Intravenous pyelography
Hip film (single view)
Mammography
Barium enema or small bowel series
CT† scan of head or chest
CT scan of abdomen and lumbar spine
CT pelvimetry
0.02–0.07 mrad
100 mrad
≥ 1 rad*
200 mrad
7–20 mrad
2–4 rad
<1 rad
3.5 rad
250 mrad
*Exposure depends on the number of films
†
Abbreviation: CT, computed tomography
Data from Cunningham FG, Gant NF, Leveno KJ, Gilstrap LC 3rd, Hauth
JC, Wenstrom KD. General considerations and maternal evaluation. In:
Williams obstetrics. 21st ed. New York (NY): McGraw-Hill; 2001.
p. 1143–58.
ably very small. It is estimated that a 1–2 rad fetal
exposure may increase the risk of leukemia by a factor of 1.5–2.0 over natural incidence and that an
estimated 1 in 2,000 children exposed to ionizing
radiation in utero will develop childhood leukemia.
This is increased from a background rate of approximately 1 in 3,000 (2, 10). If elective abortion were
chosen in every instance of fetal exposure to radiation, 1,999 exposed, normal fetuses would be aborted
for each case of leukemia prevented (2, 11). It has
been estimated that the risk of radiation-induced carcinogenesis may indeed be higher in children compared with adults, but such risks are not likely to
exceed 1 in 1,000 children per rad (12). Thus, abortion should not be recommended solely on the basis
of exposure to diagnostic radiation.
Ultrasonography
Ultrasonography involves the use of sound waves and
is not a form of ionizing radiation. There have been no
reports of documented adverse fetal effects for diagnostic ultrasound procedures, including duplex
Doppler imaging. Energy exposure from ultrasonography has been arbitrarily limited to 94 mW/cm2 by
the U.S. Food and Drug Administration. There are no
contraindications to ultrasound procedures during
pregnancy, and this modality has largely replaced Xray as the primary method of fetal imaging during
pregnancy.
VOL. 104, NO. 3, SEPTEMBER 2004
Magnetic Resonance Imaging
With MRI, magnets that alter the energy state of
hydrogen protons are used instead of ionizing radiation (13). This technique could prove especially
useful for diagnosis and evaluation of fetal central
nervous system anomalies and placental abnormalities (eg, accreta, previa).
Nuclear Medicine
Nuclear studies such as pulmonary ventilation–perfusion, thyroid, bone, and renal scans are performed
by “tagging” a chemical agent with a radioisotope.
The fetal exposure depends on the physical and biochemical properties of the radioisotope (6).
Technetium Tc 99m is one of the most commonly used isotopes and is used for brain, bone,
renal, and cardiovascular scans. In general, these latter procedures result in a uterus, embryo, or fetal
exposure of less than 0.5 rad (6, 12).
One of the more common nuclear medicine
studies performed during pregnancy is the ventilation–perfusion scan for suspected pulmonary
embolism. Macroaggregated albumin labeled with
Technetium Tc 99m is used for the perfusion portion, and inhaled xenon gas (127Xe or 133Xe) is used
for the ventilation portion. The amount of radiation
to which the fetus is exposed is extremely small
(approximately 50 mrad) (14).
In a 2002 study, investigators calculated the
mean fetal radiation exposure resulting from helical (spiral) CT in healthy pregnant women and
compared it with reported fetal radiation doses
for ventilation–perfusion lung scanning (approximately 100–370 µGy) (15). Although the exposure
from ventilation–perfusion is relatively low, the
study found that the mean fetal doses associated
with helical CT were lower. Although exposure
varied with gestational age (3.3–20.2 µGy for
the first trimester, 7.9–76.7 µGy for the second
trimester, and 51.3–130.8 µGy for the third
trimester), 20 of 23 study patients exhibited a
mean fetal dose of less than 60 µGy for all 3
trimesters.
Radioactive iodine readily crosses the placenta
and can adversely affect the fetal thyroid, especially
if used after 10–12 weeks of gestation. Radioactive
isotopes of iodine used for treatment of hyperthyroidism are contraindicated during pregnancy, and
such therapy should be delayed until after delivery.
If a diagnostic scan of the thyroid is essential,
ACOG Committee Opinion No. 299 Guidelines for Diagnostic Imaging
During Pregnancy
649
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I or Technetium Tc 99m should be used in place
of 131I (14).
3.
Contrast Agents
A variety of oral and intravascular contrast agents
are used with X-ray and magnetic imaging procedures. Most radiopaque agents used with CT and
conventional radiography contain derivatives of
iodine and have not been studied in humans; however iohexol, iopamidol, iothalamate, ioversol,
ioxaglate, and metrizamide have been studied in animals and do not appear to be teratogenic (16).
Neonatal hypothyroidism has been associated with
some iodinated agents taken during pregnancy (17).
For this reason, these compounds generally are
avoided unless essential for correct diagnosis.
Studies requiring views before and after the administration of contrast agents will necessarily have
greater radiation exposure. Although some
radiopaque agents pass into the breast milk, they
have not been associated with problems in nursing
babies (16).
Paramagnetic contrast agents used during MRI
have not been studied in pregnant women. Animal
studies have demonstrated increased rates of spontaneous abortion, skeletal abnormalities, and visceral
abnormalities when given at 2–7 times the recommended human dose (18, 19). It is not known if these
compounds are excreted into human milk. Generally,
these agents should be used during pregnancy only if
the potential benefit justifies the potential risk to the
fetus as demonstrated in animal studies.
Guidelines
The following guidelines for X-ray examination or
exposure during pregnancy are suggested:
1. Women should be counseled that X-ray exposure from a single diagnostic procedure does not
result in harmful fetal effects. Specifically,
exposure to less than 5 rad has not been associated with an increase in fetal anomalies or pregnancy loss.
2. Concern about possible effects of high-dose ionizing radiation exposure should not prevent
medically indicated diagnostic X-ray procedures from being performed on a pregnant
woman. During pregnancy, other imaging procedures not associated with ionizing radiation
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During Pregnancy
4.
5.
6.
(eg, ultrasonography, MRI) should be considered instead of X-rays when appropriate.
Ultrasonography and MRI are not associated
with known adverse fetal effects.
Consultation with an expert in dosimetry calculation may be helpful in calculating estimated
fetal dose when multiple diagnostic X-rays are
performed on a pregnant patient.
The use of radioactive isotopes of iodine is contraindicated for therapeutic use during pregnancy.
Radiopaque and paramagnetic contrast agents
are unlikely to cause harm and may be of diagnostic benefit, but these agents should be used
during pregnancy only if the potential benefit
justifies the potential risk to the fetus.
References
1. Gray JE. Safety (risk) of diagnostic radiology exposures.
In: American College of Radiology. Radiation risk: a
primer. Reston (VA): ACR; 1996. p. 15–7.
2. Brent RL. The effect of embryonic and fetal exposure to
x-ray, microwaves, and ultrasound: counseling the pregnant and nonpregnant patient about these risks. Semin
Oncol 1989;16:347–68.
3. Hall EJ. Scientific view of low-level radiation risks.
Radiographics 1991;11:509–18.
4. Moore MM, Shearer DR. Fetal dose estimates for CT
pelvimetry. Radiology 1989;171:265–7.
5. Parry RA, Glaze SA, Archer BR. The AAPM/RSNA
physics tutorial for residents. Typical patient radiation
doses in diagnostic radiology. Radiographics 1999;19:
1289–302.
6. Cunningham FG, Gant NF, Leveno KJ, Gilstrap LC 3rd,
Hauth JC, Wenstrom KD. General considerations and
maternal evaluation. In: Williams obstetrics. 21st ed. New
York (NY): McGraw-Hill; 2001. p. 1143–58.
7. Otake M, Yoshimaru H, Schull WJ. Severe mental retardation among prenatally exposed survivors of the atomic
bombing of Hiroshima and Nagasaki: a comparison of
the T65DR and DS86 dosimetry systems. Technical
report; RERF TR 87-16. Hiroshima: Radiation Effects
Research Foundation; 1988.
8. National Research Council. Other somatic and fetal
effects. In: Health effects of exposure to low levels of ionizing radiation: BEIR V. Washington, DC: National
Academy Press; 1990:352–70.
9. Schull WJ, Otake M. Neurological deficit among survivors exposed to the atomic bombing of Hiroshima and
Nagasaki: a reassessment and new directions. In: Kriegel
H, Schmahl W, Gerber GB, Stieve FE, editors. Radiation
risks to the developing nervous system. Neuherberg, June
18-29, 1985, Munich. Stuttgart: G Fischer Verlag; 1986.
p. 399–419.
OBSTETRICS & GYNECOLOGY
10. Miller RW. Epidemiological conclusions from radiation
toxicity studies. In: Fry RJ, Grahn D, Griem ML, Rust JH,
editors. Late effects of radiation: proceedings of the colloquium held at the Center for Continuing Education, the
University of Chicago, Illinois, May 1969. New York
(NY): Van Nostrand Reinhold; 1970. p. 245–56.
11. Early diagnosis of pregnancy: a symposium. J Reprod
Med 1981;26(suppl 4):149–78.
12. Mettler FA Jr, Guiberteau MJ. Essentials of nuclear medicine imaging. 4th ed. Philadelphia (PA): WB Saunders;
1998.
13. Curry TS 3rd, Dowdey JE, Murry RC Jr, editors.
Christensen’s physics of diagnostic radiology. 4th ed.
Philadelphia (PA): Lea & Febiger; 1990.
14. Ginsberg JS, Hirsh J, Rainbow AJ, Coates G. Risks to the
fetus of radiologic procedures used in the diagnosis of
maternal venous thromboembolic disease. Thromb
Haemost 1989;61:189–96.
15. Winer-Muram HT, Boone JM, Brown HL, Jennings SG,
Mabie WC, Lombardo GT. Pulmonary embolism in
VOL. 104, NO. 3, SEPTEMBER 2004
16.
17.
18.
19.
pregnant patients: fetal radiation dose with helical CT.
Radiology 2002;224:487–92.
Radiopaque agents (diagnostic). MedlinePlus drug information. Available at: http://www.nlm.nih.gov/medlineplus/
druginfo/uspdi/202997.html. Retrieved June 17, 2004.
Mehta PS, Metha SJ, Vorherr H. Congenital iodide goiter
and hypothyroidism: a review. Obstet Gynecol Surv
1983;38:237–47.
Gadodiamide (systemic). In: USP DI: drug information
for the health care professional. 24th ed. Greenwood
Village (CO): Microdemex; 2004. Available at http://uspdi.
micromedex.com/v1/excluded/Gadodiamide(Systemic).
pdf. Retrieved June 17, 2004.
Gadoteridol (systemic). In: USP DI: drug information for
the health care professional. 24th ed. Greenwood Village
(CO): Microdemex; 2004. Available at: http://uspdi.
micromedex.com/v1/excluded/Gadoteridol(Systemic).pdf.
Retrieved June 17, 2004.
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