Pregnancy Screening Strategies for Diagnostic Nuclear Medicine: Survey Results from Australia and New Zealand

Policy and Regulations

This study revealed a low awareness of government and international regulations concerning pregnancy and medical radiation. Most participants reported that they had not read the relevant sections regarding pregnancy and diagnostic procedures in ICRP 84 (3) or ARPANSA 14.2 (4), which correlates with the findings from a previous interview study conducted by the authors (7).

ICRP publication 84, Pregnancy and Medical Radiation, is one of the primary international documents detailing recommendations for the use of ionizing radiation in pregnant and potentially pregnant women. Chapter 6 discusses radiation protection applicable to nuclear medicine. It states that for “women of childbearing age, the possibility of pregnancy and the justification for the examination should be considered.” It recommends that patients be “carefully interviewed” to determine their pregnancy status and that “discretion” is required in the case of adolescents. It also states that “advisory notices should be posted” in the nuclear medicine department.

ARPANSA 14.2, Safety Guide for Radiation Protection in Nuclear Medicine, was published by the Australian government to provide advice on radiation practice. Section 5 discusses the protection of the embryo or fetus. It states that “all female patients of child bearing age” should be questioned regarding their pregnancy status “immediately before the procedure”; the reason for asking should be explained to the patient “to avoid the patient taking offense and not answering fully”; this type of discussion “requires tact and discretion”; asking teenagers may be a “sensitive issue”; an interpreter may be required when language barriers exist; and that patient history alone “may not be reliable.” The guide lists several circumstances for when the likelihood of pregnancy is low or physically impossible. These include hysterectomy, tubal ligation, normal menstrual period within the last 10 d (if the patient has regular menstrual periods), contraceptive measures having been taken (providing they have been taken regularly), and no sexual relationship for several months. If pregnancy status is uncertain, “the nuclear medicine specialist should be consulted” to decide whether to postpone the study, perform a pregnancy test, or continue with the study. This decision may be influenced by the “level of radiation dose” from the procedure.

Current Practice

The age range to include for questioning about pregnancy has not been clearly defined. The use of the term “childbearing age” in radiation protection documents refers to any female capable of reproduction. Both the age at menarche and the age at menopause are individual and can vary greatly among women.

The age at menarche is primarily influenced by genetic factors but also by nutrition, geography, and altitude (8). In a study investigating age at menarche in 34 countries, Currie et al. (9) reported that “in 95% of individuals, age at menarche ranged between 10 y 6 mo and 14 y 11 mo.” Several studies (8,10,11) discuss whether there has been a decline in the age of menarche over the past 50 y. Declining age at menarche has been associated with obesity (11). Some studies report a decline in age from 13 to 12 y since the early 20th century, but that in the latter part of the century age of menarche appears stable (8,10). Posner (10) reports that the “reference range for onset of menarche in the Unites States is now considered 10–14 y.”

The age at natural menopause varies greatly among women. Factors believed to influence age at menopause include ethnicity, location, smoking, body mass index, physical activity, and number of children (12). A large Australian study of 5,961 twin females by Do et al. reported the median age at natural menopause as 51 y (13). Another study of 5,288 women by Dratva et al., conducted in 9 European countries, reported the median age at menopause as 54 y (12). Surgically induced menopause (hysterectomy or tubal ligation) is associated with earlier timing of menopause (12).

Participants in our study reported using age at menarche as the rationale for applying a particular minimum age to question patients from 10 y and up to 16 y of age. Age of menopause was used as the rationale for choosing a particular maximum age between 40 and 60 y. These choices imply a lack of knowledge regarding these 2 aspects of female physiology and reproduction and possible reliance on personal interpretation and experience. Because both menarche and menopause can occur at different ages in individual women, it may be prudent to first ask whether the patient has either begun menstruating (for young teenagers) or completed menstruating (for women over 50 y of age) or ask the date of the LMP, rather than beginning with a question asking if the patient might be pregnant.

Although 65% of participants indicated they had a written department policy for questioning patients, few stated this as their rationale for the minimum or maximum age to question patients. This may be due to departmental policies that use wording similar to that used in radiation protection documents, which refer to women of childbearing age but do not define the age range or how to determine who is classed as childbearing. For minimum age, many participants commented that selection of patients to question was dependent on the patient’s perceived maturity, implying that some nuclear medicine personnel make assumptions about the patient when determining pregnancy status.

The American College of Radiology recommends that “all patients of menstrual age (typically ages 12 through 50 y) should be questioned about pregnancy status using a standardized form or through direct questioning by the technologist.” In addition, it recommends the use of a standardized form to ensure uniformity in the questioning process (5). Variations in practice can lead to individual patients being treated differently and consequently not receiving the same level of care. Gabel and Shipan state that reducing practice variation is “a fundamental issue for increasing the quality of health care” (14). The development of a standardized form to determine pregnancy status may assist nuclear medicine personnel in ensuring that the appropriate patients are asked appropriate questions. Our study showed a wide variation in the methods used to determine which patients to question and which questions they were asked. Verbal questioning of the patient is still predominately used, with or without the addition of the patient’s signature, and this may be a contributing factor to inconsistencies in practice.

Pregnancy testing is not routinely used before diagnostic nuclear medicine imaging procedures. Pregnancy testing for all female patients would be unnecessary, time-consuming, and expensive (7). Urine pregnancy tests are relatively inexpensive and easy to use; however, if used before the date of missed menses they have been reported to have a high false-negative rate (15). The most commonly reported circumstance for using pregnancy testing is when the patient is unsure of her pregnancy status. The reliability of patient history and self-assessment of pregnancy status has been reported with conflicting results (16,17). Minnerop et al. (18) investigated the reliability of patient assessment to exclude pregnancy and found that women are able to exclude pregnancy. They reported a 100% negative predictive value for women stating pregnancy was impossible. They suggest that history of tubal ligation, intrauterine device, or oral contraceptive use should not be relied on to exclude pregnancy. Minnerop et al. recommended using patient history and suspicion of pregnancy and weighing these against the risk associated with an undiagnosed pregnancy to decide if a pregnancy test is warranted.

A small number of participants indicated that they used pregnancy testing if the radiation dose from a procedure was considered high. This is recommended in ARPANSA 14.2 (4); however, a definition of higher dose is not provided. Diagnostic nuclear medicine procedures are generally considered low-dose procedures, with most ^99mTc procedures giving an effective dose of less than 10 mSv to an adult patient (1). Because the dose is quite low for these procedures, it may be sufficient to rely on patient self-assessment of pregnancy status and to use pregnancy testing only where there is concern or doubt surrounding the patient’s responses. Other procedures that use longer-lived radioisotopes, positron emission, or hybrid CT imaging may provide a higher effective dose to the patient and therefore would warrant the use of pregnancy testing before administration of the radiopharmaceutical.

Radiation Risk to Fetus

Estimation of fetal dose from maternal examinations can be difficult. Calculation of fetal dose estimates must include factors such as the physical properties of the radionuclide, the administered activity, and the stage of fetal development. The chemical and biologic properties of the radiopharmaceutical must be considered to determine the amount of placental transfer and biodistribution in fetal tissues. External irradiation of the fetus from maternal organs also adds to the dose (19). The fetal doses from most diagnostic nuclear medicine procedures are “much lower than the levels where developmental and neurologic effects are known to occur” (4). However, the dose levels have been reported to be associated with “a slightly increased risk of childhood cancer or leukaemia” (4). Although the risks to the fetus are low, anxiety and distress may be caused if a woman is irradiated and subsequently finds out she is pregnant. The participants in this study ranked several commonly performed procedures according to their radiation risk to the fetus, and although only a small number of participants correctly ranked every procedure, most participants were able to identify the risks as low, medium, and high.