Stop using the hCG discriminatory zone of 1,500 to 2,000 mIU/mL to guide intervention during early pregnancy

Approximately 15% of early pregnancies are complicated by pelvic or abdominal pain and uterine bleeding or spotting. In these situations, you must determine whether your patient has a viable intrauterine pregnancy, a pregnancy that will end in a miscarriage (spontaneous abortion), or an ectopic pregnancy.

To guide you to the correct diagnosis, a medical history and physical examination can be helpful. For example, a woman with a prior ectopic pregnancy who now has an early pregnancy complicated by pelvic pain and uterine bleeding is at high risk for an ectopic pregnancy. Physical examination also is important; if the pelvic examination reveals a dilated cervix with pregnancy tissue in the cervical os it is likely that a miscarriage is in progress. For most cases of early pregnancy complicated by pelvic pain and/or uterine bleeding, however, a pelvic sonogram and serial quantitative ­measurement of ­human chorionic gonadotropin (hCG) are needed to achieve the correct diagnosis.

Here I outline the clinical markers for transvaginal ultrasonography that indicate a viable or failed intrauterine pregnancy as well as an ectopic pregnancy. I also present data on single vs serial hCG measurement and discuss serial hCG levels that indicate viable or nonviable intrauterine or ectopic ­pregnancy.

Is an early gestation viable? Clinical evaluationTransvaginal pelvic ultrasoundTransvaginal and transabdominal ultrasonography play a critical role in evaluating early pregnancy problems. In a normal pregnancy, key developmental milestones that can be observed reliably on ultrasound are^1,2:

A pelvic ultrasound also may provide evidence that an intra­uterine pregnancy will fail and result in a miscarriage. Findings diagnostic of a failed intrauterine pregnancy ­include³:

Findings suspicious for a failing intrauterine pregnancy include³:

When it’s an ectopic pregnancy. ­Definitive ultrasonographic evidence of an ectopic pregnancy is identification of a fetal heartbeat outside the uterus or a gestational sac and yolk sac outside of the uterus. An adnexal mass can be identified on ultrasonography in most cases of ectopic pregnancy. In one study of 291 ectopic pregnancies, an adnexal mass was identified in 94% of cases, and a moderate to large amount of free pelvic fluid was found in 36% of cases.⁴ The adnexal masses included nonspecific (54% of all ectopic cases), a tubal ring without a yolk sac or embryo (25%), a yolk sac but no embryonic heartbeat (8%), and an embryo with cardiac activity (7%).

In clinical units with high-­quality gynecologic ultrasonography available, most ectopic pregnancies will be detected on initial scan and only 10% to 15% of ectopic pregnancies will have an ultrasound finding of no intrauterine pregnancy and no evidence for an extrauterine pregnancy.⁵

Almost all (in the range of 99%) viable intrauterine pregnancies demonstrate an increase in hCG level of 53% or more over 48 hours, whereas only 21% of ectopic pregnancies demonstrate a rise of 53% or more.⁷

Most pregnancies that will end in a miscarriage demonstrate a decrease in hCG level over 48 hours. If the initial hCG value is 2,000 mIU/mL, 90% of pregnancies that will end in miscarriage will have an approximate 30% decrease in hCG over 48 hours. If the initial hCG is 1,000 mIU/mL, 95% of spontaneous abortions will have a 28% decline in 48 hours.⁷ About 10% of ectopic pregnancies also will demonstrate a 30% decrease in hCG over 48 hours.

A minor disadvantage of serial hCG measurements is that patients may become anxious and fearful as they await the result of life-altering test results.