Low lying placenta: natural course, clinical data, complications and a new model for early prediction of persistency.

OBJECTIVE: To define the natural course and complications, and develop a model for predicting persistency when low-lying placenta (LLP) is detected early in pregnancy.

METHODS: This retrospective cohort study included women with LLP detected during an early anatomic scan performed at 13-16 weeks gestation. Additional transvaginal ultrasound exams were assessed for resolution at 22-24 weeks and 36-39 weeks. Patients were categorized as: Group 1-LLP resolved by the second-trimester scan, Group 2-LLP resolved by the third trimester, or Group 3-LLP persisted to delivery. Clinical and laboratory parameters, as well as maternal and neonatal complications, were compared. A linear support vector machine classification was used to define a prediction model for persistent LLP.

RESULTS: Among 236 pregnancies with LLP, 189 (80%) resolved by 22-24 weeks, 25 (10.5%) resolved by 36-39 weeks and 22 (9.5%) persisted until delivery. Second trimester hCG levels were higher the longer the LLP persisted (0.8 ± 0.7MoM vs. 1.13 + 0.4 MoM vs. 1.7 ± 1.5 MoM, adjusted p  = .03, respectively) and cervical length (mm) was shorter (first trimester: 4.3 ± 0.7 vs. 4.1 ± 0.5 vs. 3.6 ± 1; adjusted p  = .008; Second trimester: 4.4 ± 0.1 vs. 4.1 ± 1.2 vs. 3.8 ± 0.8; adjusted p  = .02). The predictive accuracy of the linear support vector machine classification model, calculated based on these parameters, was 90.3%.

CONCLUSIONS: Persistent LLP has unique clinical characteristics and more complications compared to cases that resolved. Persistency can be predicted with 90.3% accuracy, as early as the beginning of the second trimester by using a linear support vector machine classification model.