The use of sonography for any nonmedical purpose, such as "keepsake fetal imaging," is considered contray to responsible medical practice and is not condoned by the Food and Drug Administration (2014), the American Institute of Ultrasound in Medicine (2012, 2013b), or the American College ofObstetricians and Gynecologists (2016).
The reported prevalence of work-related musculoskeletal discomfort or injury among sonographers approximates 70 percent Ganga, 2012; Roll, 2012). The main risk factors for injury during transabdominal ultrasound examinations are awkward posture, sustained static forces, and various pinch grips used while maneuvering the transducer (Centers for Disease Control and Prevention, 2006). Maternal habitus can be contributory because more force is oten employed when imaging obese patients.
The following guidelines may help avert injury: 1. Position the patient close to you on the examination table.
As a result, your elbow is close to your body, shoulder abduction is less than 30 degrees, and your thumb is facing up.
2.
Adjust the table or chair height so that your forearm is parallel to the floor.
3.
If seated, use a chair with back support, support your feet, and keep ankles in neutral position. Do not lean toward the patient or monitor.
4.
Face the monitor squarely and position it so that it is viewed at a neutral angle, such as 15 degrees downward.
5.
Avoid reaching, bending, or twisting while scanning.
6.
Frequent breaks may prevent muscle strain. Stretching and strengthening exercises can be helpful.
The earlier that sonography is performed, the more accurate the gestational age assessment. Specific criteria for "re-dating" a pregnancy, that is, reassigning the gestational age and estimated date of delivery using initial sonogram findings, are shown in Table 1 0-1. The only exception to revising the gestational age based on early sonography is if the pregnancy resulted from assisted reproductive technology, in which case accuracy of gestational age assessment is presumed.
Sonographic measurement of the crown-rump length (CRL) is the most accurate method to establish or conirm gestational
TABLE 10-1. Sonographic Gestational Age Assessment
Gestational Age Parameter(s) to Revisea 9 to <14 wks CRL 14 to <16 wks BPO, HC AC FL 16 to <22 wks BPO, HC AC FL >10 d 22 to <28 wks BPO, HC AC FL >14d :28 weeks BPOt HC AC FL >21 d aSonographic gestational age should be used when the LMP-derived gestational age differs from that obtained with sonography by the threshold value.
abdominal circumference; BPO biparietal diameter; CRL = crown-rump length; FL = femur length; HC = head circumference; LMP = last menstrual period. Modified from American College of Obstetricians and Gynecologists,l2017b.
FIGURE 10-1 The measured crown-rump length in this 12-week 3-day fetus approximates 6 cm.
age (Appendix, p. 1263). As noted, transvaginal imaging typi cally yields higher resolution images. The CL is measured in the midsagittaleplane with the embryo or fetus in a neutral, nonlexed position so that its length can be measured in a straight line (Fig.
The measurement should include neither the yolk sac nor a limb bud. The mean of three discrete measurements is used. Until 136/7 weeks' gestation, the CL is accurate to within 5 to 7 days (American College of Obstetricians and Gynecologists, 201 7b).