no visible intrauterine or extrauterine gestation on ultrasound even though hCG is positive
Patients with pregnancies below the discriminatory zone often have nondiagnostic ultrasound findings (eg, small pseudosac [centrally located fluid collection], no adnexal masses) and therefore are diagnosed with a pregnancy of unknown location: the pregnancy could be intrauterine (viable or nonviable) or extrauterine (ie, ectopic).
If transabdominal ultrasonography cannot locate the pregnancy, transvaginal ultrasonography is performed because it is more sensitive and can better visualize the adnexa, particularly in obese patients or those with an early gestation.
In first trimester, this graph is for pregnancy of unknown origin not suspected ectopic only
<aside> 💡 discriminatory zone [β-hCG <3,500 mIU/mL]: the threshold at which a gestational sac should be visible on ultrasound if the pregnancy is intrauterine
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<aside> 💡 Once an intrauterine pregnancy with cardiac motion is identified, β-hCG levels do not change management and therefore are not measured.
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The most common cause of a pregnancy of unknown location is early gestation of a normal intrauterine pregnancy; however, other potential etiologies are a completed spontaneous abortion, nonviable intrauterine pregnancy (missed abortion), and ectopic pregnancy, all of which require further evaluation for definitive diagnosis.
Because each type of pregnancy follows a characteristic β-hCG pattern, quantitative β-hCG levels are repeated every 48 hours:
Early but viable intrauterine pregnancies typically have a ≥35%-50% rise in β-hCG every 48 hours.
Completed spontaneous abortions cause β-hCG levels to decrease precipitously because the pregnancy has been evacuated.
Ectopic and nonviable intrauterine pregnancies (eg, anembryonic gestations) usually cause <35% rise in β-hCG due to abnormal pregnancy development.
Anembryonic gestation (Blighted ovum)
Serial quantitative β-hCG measurements until the level reaches the discriminatory zone, at which point a repeat transvaginal ultrasound is preformed if results are still equivocal→
Anti-D immunoglobulin in spontaneous abortion, ectopic pregnancy
Higher serum progesterone levels are usually associated with normal, viable intrauterine pregnancies (and lower levels with ectopic or nonviable intrauterine pregnancies). However, levels are not diagnostic for ectopic pregnancy due to low sensitivity and specificity; therefore, measurement is not indicated.