Prospective cross-validation of three methods of predicting failing pregnancies of unknown location

We compared the performance of each of three tests for predicting pregnancy failure in the pregnancy of unknown (PUL) population.

In a prospective observational study, we compared the performance of three models for the prediction of pregnancy failure in women with a PUL: (i) logistic-regression model incorporating vaginal bleeding, endometrial thickness (ET), initial serum progesterone and hCG levels; (ii) serum progesterone at 0 h; and (3) the hCG ratio.

A total of 5942 consecutive pregnant women attending the Early Pregnancy Unit were scanned and 439 (7.4%) were classified as PULs. Of these women, 420 had complete data for serum hCG at 0 and 48 h, the hCG ratio, serum progesterone at 0 h, vaginal bleeding and ET. The final outcomes were 219 (52.1%) failing PULs, 167 (39.8%) intra-uterine pregnancies and 34 (8.1%) ectopic pregnancies. For the prediction of pregnancy failure in the PUL population, the area under the receiver operating characteristic (ROC) curve (AUC) for the logistic-regression model was 0.907 (Standard error (SE) 0.015), the AUC for serum progesterone was 0.952 (SE 0.010) and the AUC for the hCG ratio was 0.980 (SE 0.004). This improved performance of the hCG ratio was significant when compared with that of initial serum progesterone (P = 0.0076) and the logistic-regression model (P < 0.0001). Using the hCG ratio cut-offs of < 0.87 and 70% for the prediction of failing PUL, sensitivities were 86.3 and 82.2% (S), 87.2% (NS) and 78.1% (S), specificities were 97.0 and 98.0% (NS), 89.6% (S) and 88.6% (S), positive-likelihood ratios were 28.91, 41.30, 8.34 and 6.82 and negative-likelihood ratios were 0.14, 0.18, 0.14 and 0.25, respectively.

The hCG ratio seems to be an optimal test for the prediction of pregnancy failure in a PUL population. The hCG ratio cut-off of 0.79 is recommended on the basis of minimizing risk to those PULs discharged at 48 h. Most importantly, when the hCG ratio is below a particular cut-off, these women can be discharged at 48 h without intervention and need for further follow-up.