Sonography of pregnancies with first-trimester bleeding and a small intrauterine gestational sac without a demonstrable embryo

Objective: This was a prospective observational cohort study to evaluate the outcome and prognostic criteria of pregnancies with first-trimester bleeding and a gestational sac <or=16 mm without a demonstrable embryo.

Methods: Criteria for admission into the study included: (1) first-trimester bleeding; (2) a transvaginal scan performed upon admission demonstrating a single intrauterine gestational sac with a mean diameter <or=16 mm and without a demonstrable embryo. The outcome variable was miscarriage, defined as pregnancy loss prior to 22 weeks. The following explanatory variables were considered: maternal age, menstrual age, size of the gestational sac, presence or absence of the yolk sac and subchorionic hematoma, and beta-human chorionic gonadotropin levels. The relationship of these variables with pregnancy failure was analyzed by stepwise logistic regression.

Results: Of 50 patients, 32 (64%) underwent miscarriage. The receiver-operating characteristics (ROC) curve of the size of the gestational sac demonstrated a high level of statistical significance (area under the ROC curve 0.9080, P < 0.000001) and stepwise logistic regression revealed that this was the only variable independently correlated with the subsequent occurrence of miscarriage.

Discussion: It is commonly accepted that in pregnant patients with first-trimester bleeding, demonstration by transvaginal ultrasound of an intrauterine gestational sac <or=16 mm without an embryo may be compatible with a viable pregnancy. Our results suggest that in general this finding is associated with a poor outcome, with miscarriage occurring in two-thirds of patients. When the sac is small for gestational age, the risk of miscarriage is greatly increased. In the present series, a gestational sac diameter less than -1.34 standard deviations of the mean was associated with pregnancy failure in over 90% of cases.