Other rare causes of positive assays without pregnancy are: (1) exogenous hCG injection used for weight loss, (2) renal fail ure with impaired hCG clearance, (3) physiological pituitary hCG, and (4) hCG-producing tumors that most commonly originate from gastrointestinal sites, ovary, bladder, or lung (Montagnana, 2011).
Over-the-counter pregnancy test kits have been available since the early 1970s, and millions are sold annually in the United States. More than 60 such tests are available in this country (Grenache, 2015). Unfortunately, many of these are not as accurate as advertised Gohnson, 2015). For example, Cole and associates (201i1) found that a detection limit of 12.5 mIU/mL would be required to diagnose 95 percent of pregnancies at the time of missed menses, but they reported that only one brand had this degree of sensitivity. Two other brands gave false-positive or invalid results. In fact, with an hCG concentration of 100 mIU/mL, clearly positive results were displayed by only 44 percent of brands. Accordingly, only about 15 percent of pregnancies could be diagnosed at the time of the missed menses. Some manufacturers of even newer home urine assays claim >99-percent accuracy of tests done on the day of-and some up to 4 days before-the expected day of menses. Again, careful analysis suggests that these assays are often not as sensitive as advertised Gohnson, 2015).
• Sonographic Recognition of Pregnancy
Transvaginal sonography has revolutionized early pregnancy imaging and is commonly used to accurately establish gestational age and conirm pregnancy location. A gestational sac-a small anechoic luid collection within the endometrial cavityis the irst sonographic evidence of pregnancy. It may be seen with transvaginal sonography by 4 to 5 weeks' gestation. A luid collection, however, can also be seen within the endometrial cavity with an ectopic pregnancy and is termed a pseudogestational sac or pseudosac (Fig. 19-4, p. 375). Thus, further evaluation may be warranted if this is the only sonographic inding, particularly in a woman with pain or bleeding. A normal
FIGURE 9-3 Transvaginal sonogram of a first-trimester intrauterine pregnancy. The double decidual sign is noted surrounding the gestational sac and is defined by the decidua parietalis (white asterisk) and the decidua capsularis (yellow asterisk). The arrow notes the yolk sac, and the crown-rump length of the embryo is marked with measuring calipers. (Used with permission from Dr. Elysia Moschos.) gestational sac implants eccentrically in the endometrium, whereas a pseudosac is seen in the midline of the endometrial cavity. Other potential indicators of early intrauterine pregnancy are an anechoic center surrounded by a single echogenic rim-the intradecidual sign-or two concentric echogenic rings surrounding the gestational sac-the double decidual sin shown in Figure 9-3. If sonography yields equivocal indings, the term pregnancy of unknown location (PUL) is applied. In these cases, serial serum hCG levels and transvaginal sonograms can help diferentiate a normal intrauterine pregnancy from an extrauterine pregnancy or an early miscarriage (Chap. 19, p. 373).