Pathologic basis of improving the screening utility of 2-dimensional placental morphology ultrasound

ObjectiveTo determine the utility of measuring maximum placental length in the second trimester to predict a small for gestational age placenta by weight at delivery in clinically high-risk women.Study designPlacental dimensions determined by 2-dimensional (2-D) real-time ultrasound at 19-23 weeks' gestation were compared to post-natal placental weights and pathology in 95 high-risk patients with singleton pregnancies.ResultsMaximum placental length <10.0 cm performed poorly (false positive rate 25.5%) for the detection of a small placenta by weight at delivery. Placental pathology examination revealed eccentric cord insertion to be an important explanation for poor screening test result, since this finding was significantly more common in the false negative group (length ≥10.0 cm, weight <10th percentile) compared with the true negative group (length ≥10.0 cm, weight ≥10th percentile) (15/28 vs. 9/38, Fisher's exact test, p = 0.005).ConclusionsPrediction of reduced placental weight by 2-D ultrasound determination of maximum placental length in clinically high-risk pregnancies confounded by the phenomenon of asymmetric chorion regression. Refinement of 2-D ultrasound methods to include orthogonal plane measurements, or replacement by 3-D techniques is predicted to significantly improve the effectiveness of diagnosing small placentas in-utero.