Reevaluation of discriminatory and threshold levels for serum β-hCG in early pregnancy.

OBJECTIVES: To reevaluate both discriminatory and threshold levels associated with visualization of gestational sacs, yolk sacs, and fetal poles in patients presenting with vaginal bleeding, pain, or vaginal bleeding and pain in the first trimester of pregnancy using current ultrasonographic technology.
METHODS: We reviewed the records of patients with first-trimester vaginal bleeding, pelvic pain, or both who were evaluated with a serum β-hCG level and a transvaginal ultrasonogram within 6 hours of each other and had a known pregnancy outcome. Discriminatory and threshold β-hCG levels for visualization of a gestational sac, yolk sac, and fetal pole were identified for all ultimately viable pregnancies. Logistic regression was used to model the predicted probability of visualizing these structures as a function of β-hCG values using fractional polynomials.
RESULTS: Six hundred fifty-one pregnancies met inclusion criteria; 366 were viable. Discriminatory β-hCG levels at which structures would be predicted to be seen 99% of the time were 3,510 milli-international units/mL, 17,716 milli-international units/mL, and 47,685 milli-international units/mL for gestational sac, yolk sac, and fetal pole, respectively. In our population, threshold values for β-hCG levels at which these structures could be seen were 390 milli-international units/mL, 1,094 milli-international units/mL, and 1,394 milli-international units/mL, respectively.
CONCLUSIONS: Improvements in ultrasonographic technology have led to lower threshold β-hCG values for ultrasonographic visualization of early intrauterine gestational structures. However, discriminatory levels for serum β-hCG levels were higher than values currently used in practice. LEVEL OF EVIDENCE: II.