OP19.09: Spontaneous version of fetal presentation in twin pregnancies during third trimester

Abstract

Objectives: To determine accuracy of ultrasound (US) in classifying placental cord insertion (PCI) site in multiple gestations at a tertiary care center. Methods: A retrospective study of multiple gestations delivered from 2/2003 to 7/2009 was performed. Data included gestational age (GA) at PCI identification, use of in-vitro fertilization (IVF), and PCI characterization by both US and pathology. The distance from PCI to placental edge was measured. To correlate US with pathology data, PCI was classified as central/eccentric, marginal (≤ 1 cm from placental edge), or velamentous (into membranes). Statistical analysis was performed with Chi-square comparison amongst categorical variables. US images were reviewed in discordant cases to determine causality. Results: Twins and triplets were analyzed. 638 fetuses (302 pregnancies) met criteria. Mean GA at PCI evaluation was 20.9 wks, median 19.0. Using pathology results as gold standard, US correctly identified PCI as central/eccentric, marginal, or velamentous in 69.3% (P < 0.01). US was more accurate for diamniotic-dichorionic twins (73.8% of 382) than diamniotic-monochorionic (59.4% of 155, P = 0.002). US correctly classified 97.5% of central/eccentric, 8.5% of marginal, and 6.1% of velamentous PCIs (438, 118, and 82 cases). Conversely, pathology confirmed US diagnosis of central/eccentric in 71.4%, marginal in 32.3%, and velamentous in 11.1% (of 598, 31, and 9). Comparing normal (central/eccentric) to abnormal (marginal/velamentous), US was less accurate in identifying abnormal (7.5% of 200) than normal (97.5% of 438) PCIs (P < 0.01); no difference was seen for twins (71.9% of 549) vs. triplets (73.5% of 89, P > 0.05). No difference was found in occurrence of velamentous PCI in IVF vs. non-IVF cases (12.5% for both). Conclusions: US classification of PCI was often inconsistent with pathological results in multiple gestations. Discrepant cases were evaluated and suggest evolution/peripheral infarction of the placenta with apparent evolution of the PCI in many instances.