Second Trimester Biochemical Markers as Possible Predictors of Pathological Placentation: A Retrospective Case-Control Study.

OBJECTIVE

We aimed to evaluate the association between second trimester biochemical markers and pathological placentation.

METHODS

This was a retrospective case-control study (2007-2014) of singleton gestations at a university-affiliated tertiary center. Women with pathologic placentation were subdivided into three groups: placenta accreta (group A), placenta previa (group B), or both (group C). We compared second trimester biochemical screening markers taken between 16 + 0 and 19 + 6 weeks of gestation between groups A, B, and C, and women with normal placentation (group D). Obstetrical and neonatal outcomes, risk factors for pathologic placentation, and second trimester biochemical marker values were compared between groups.

RESULTS

Overall, 301 deliveries were evaluated: 64 (21%) in group A, 66 (22%) in group B, 17 (6%) in group C, and 153 (51%) in group D. Each of the pathological placentation groups individually had a higher median alpha-fetoprotein (AFP) and human chorionic gonadotropin (hCG) multiples of median (MoM) than the controls, with the highest values of AFP and hCG observed among women with placenta accreta and the lowest values among the controls. When a multivariant analysis was applied, the hCG levels remained significantly correlated with pathological placentation. Receiver operation characteristic curves for AFP, hCG, or both were computed. For AFP the area under the ROC curve (AUC) was 0.573 (95% CI 0.515-0.630, p < 0.0274) and a cut-off value above 0.99 MoM demonstrated a sensitivity and specificity of 71 and 46%, respectively, for the prediction of pathological placentation. For hCG, the AUC was 0.662 (95% CI 0.605-0.715, p < 0.0001) and a cut-off value of 1.25 MoM demonstrated a sensitivity and specificity of 53 and 68%. When both markers were plotted, the AUC was 0.668 (95% CI 0.611-0.721, p < 0.0001) and sensitivity and specificity were 63 and 64%, respectively. A percentile MoM cut-off approach distinguished between two groups: a high-risk group (patients with AFP or hCG or both above the 75th percentile, odds ratio (OR) for pathological placentation 2.27, 95% CI 1.42-3.63), and a low-risk group (patients with AFP or hCG or both below the 25th percentile, OR for pathological placentation 0.38, 95% CI 0.24-0.60).

CONCLUSION

Second trimester biomarkers such as hCG and AFP can be used to raise a suspicion towards characterizing women into high-risk and low-risk groups for pathological placentation.