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Start With US to Diagnose Ectopic Pregnancy


 

SAN FRANCISCO — Combining an ultrasound exam and quantitative beta-hCG measurements may be the most efficient and effective way to diagnose an ectopic pregnancy, said Dr. Amy “Meg” Autry.

A decision-analysis study found that performing transvaginal ultrasound, followed by measuring beta-hCG when ultrasound results were nondiagnostic, identified all ectopic pregnancies in the fastest time (1.46 days) with the fewest interrupted intrauterine pregnancies (less than 1%). Some other diagnostic strategies were faster but less sensitive or interrupted more normal pregnancies (Obstet. Gynecol. 2001;97:464–70).

“In our hospital, in reality, we're getting ultrasound and hCGs at the same time” for women with suspected ectopic pregnancy, Dr. Autry said at a conference on antepartum and intrapartum management sponsored by the University of California, San Francisco. Some ultrasounds will show evidence of intrauterine pregnancies even when the beta-hCG results are below the “discriminatory zone”—the hCG level above which a normal intrauterine pregnancy can be visualized consistently.

Combined, the ultrasound and beta-hCG results are 97%–100% sensitive and 95%–99% specific in diagnosing ectopic pregnancy. “This is predicated on a reliable and consistent ultrasonographer—whether it's an ob.gyn. or radiologist—and you have to know what your discriminatory zone is at your institution,” said Dr. Autry of the university. At her hospital, the discriminatory zone is 1,500–1,800 mIU/mL, using an endovaginal probe.

Even in patients with beta-hCG levels below the discriminatory zone, ultrasound can identify 33% of normal intrauterine pregnancies, 28% of spontaneous miscarriages, and 25% of ectopic pregnancies, a separate study found (Obstet. Gynecol. 1999;94:583–7).

In normal early pregnancies up to 41 days' gestational age, beta-hCG levels double in 48 hours. “But once you're at 6 weeks' [gestation], you should be following by ultrasound,” Dr. Autry said, because beta-hCG levels increasingly become less accurate for identifying normal pregnancies. At 41–57 days' gestation, the beta-hCG level will increase 33% in 48 hours in normal pregnancies. At 57–65 days' gestation, beta-hCG level increases only 5% in 48 hours in normal pregnancies.

Previous data have shown that 64% of women with ectopic pregnancy up to 41 days' gestation will have normal doubling of beta-hCG, emphasizing the additional value of ultrasound examination. In early pregnancy, a beta-hCG increase of less than 50% in 48 hours invariably indicates a nonviable pregnancy, but doesn't tell you where the pregnancy is.

When ultrasound results are indeterminate, the presence of echogenic material (“I call it schmutz”) in the uterus indicates a low likelihood of a normal intrauterine pregnancy, she added. Free fluid in the cul de sac suggests a moderate risk for ectopic pregnancy, a risk that increases with increased volume or echogenicity.

Other signs in indeterminate ultrasounds can be worrisome, she said. A thick endometrial stripe with a beta-hCG level below 1,000 mIU/mL predicts an increased risk for ectopic pregnancy. An empty uterus increases the risk for ectopic pregnancy fivefold. An empty uterus plus a beta-hCG rate of change of less than 66% suggests a 25-fold increased risk for ectopic pregnancy.

Other predictors of ectopic pregnancy include a history of ectopic pregnancy or miscarriage, older age, and bleeding. Dr. Autry said she has no conflicts of interest related to these topics.

Combined, ultrasound and beta-hCG were 95%–99% specific for diagnosis.

Source DR. AUTRY

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