Low-lying placenta is associated with increased risk of hemorrhage and severe maternal morbidity: A nationwide analysis.

BACKGROUND: Placenta previa (PP) is a well-recognized obstetric complication with established maternal risks, particularly hemorrhage, that contribute significantly to maternal morbidity. In contrast, low-lying placenta (LLP) has historically been grouped with previa in both coding and clinical practice, limiting our ability to study its imparted associated outcomes as a distinct entity. However, in 2017, coding revisions allowed for a parsed diagnosis of LLP and PP and enabled the current study of differentiated associated outcomes.

OBJECTIVES: To describe and compare the independent rates of hemorrhage and severe maternal morbidity (SMM) associated with LLP and PP relative to normal placentation.

METHODS: We conducted a retrospective analysis using the Nationwide Readmissions Database (NRD) from 2017 through 2019, reflecting the initial 3 years of coding for LLP. Patients with multifetal gestation, ectopic/molar pregnancies, and other placental abnormalities were excluded. The primary outcome was hemorrhage, defined using international classification of diseases (ICD)-10 codes for ante-, intra-, and postpartum hemorrhage (PPH). SMM was defined using the Centers for Disease Control and Prevention's index, which includes a range of life-threatening complications such as disseminated intravascular coagulation, hysterectomy, and shock. Baseline characteristics and maternal outcomes were compared using chi-square tests for categorical variables and Kruskal-Wallis tests for continuous variables. Multivariable regression analysis was used to evaluate the risk ratios (RRs) of adverse outcomes across these groups.

RESULTS: Among 5,625,432 singleton deliveries, 11,486 were diagnosed with LLP and 21,356 with PP. Compared to normal placentation, LLP was associated with a significantly higher rate of hemorrhage (21.1% vs. 4.0%, p < 0.001), SMM (4.5% vs. 1.8%, p < 0.001), maternal blood transfusion (3.3% vs. 1.1%, p < 0.001), hysterectomy (0.2% vs. < 0.1%, p < 0.001), and hysterectomy within 30 days (0.2% vs. 0.0%, p < 0.001). LLP was also associated with longer median hospital stay (3 vs. 2 days, p < 0.001) and higher total charges ($21,410 vs. $17,024; p < 0.001). In adjusted analyses using normal placentation as the referent group, LLP remained independently associated with hemorrhage (adjusted relative risk [aRR], 4.72; 95% CI, 4.56-4.89), SMM (aRR, 2.16; 95% confidence interval [CI], 1.99-2.35), and transfusion (aRR, 2.61; 95% CI, 2.36-2.88). PP was associated with even higher risks of hemorrhage (aRR, 8.93), SMM (aRR, 4.22), and transfusion (aRR, 5.69) compared to those with normal placentation (all p < 0.001).

CONCLUSION: With the institution of distinct coding for LLP in 2017, we were able to distinguish between patients with LLP and PP. While PP remains associated with the highest risk of poor maternal outcomes, patients with an antenatal diagnosis of LLP also have an increased risk of hemorrhage and SMM relative to those with normal placentation. These findings should be considered during the prenatal counseling and management of patients with LLP.