P25.03: Incidence of invasive placental disorders after Caesarean section

Abstract

The aim of this study was to ascertain the incidence and prenatal diagnosis of disorders of invasive placentation in a prospectively assembled cohort of women with previous Caesarean delivery and third trimester placenta previa. Women with anterior placenta previa (placenta covering internal os or edge within 2.0 cms ≥ 36 weeks) were identified from electronic records of fetal medicine unit. The previous obstetric history was reviewed. Women with a low posterior placenta and those referred from other hospitals were excluded from the analysis. The diagnosis of invasive placentation was confirmed at histopathology or from the operating records, and was matched with records of all women with invasive placentation to identify undiagnosed cases. Predictive accuracy of third trimester ultrasound in detecting these disorders was calculated as sensitivity, specificity, positive (PPV) and negative (NPV) predictive values, and positive (LR +ve) and negative (LR -ve) likelihood ratios were generated. In a routinely screened population, 134 women with placenta previa in the third trimester or low anterior placenta ≥ 36 weeks were identified. 53 of these had a history of at least one Caesarean section. Nine women were diagnosed with invasive placentation. None of the women where the placental edge did not overlap the internal os had invasive placentation. In the 23 women where the placental edge overlapped the internal os, invasive placentation was found in nine women (39.1%, 95% CI: 22.1 to 59.3%). Predictive accuracy of third trimester ultrasound was as follows: sensitivity: 88.9%, specificity: 80.0%, PPV: 72.7%, NPV: 92.3%, LR +ve: 4.4, LR -ve: 0.14. In women with previous Caesarean delivery, invasive placentation is unlikely to be encountered unless the placental edge completely covers the internal os. In this sub-group of women, the incidence of disorders of invasive placentation 39%, and is higher than previously reported. Prenatal dedicated ultrasound assessment of these pregnancies is warranted in order to accurately identify these conditions.