A Cross Sectional Study of Second Trimester Sonographically Diagnosed Low-Lying Placenta and Associated Maternal and Neonatal Outcomes at Delivery

Background: The optimal management of patients diagnosed in the mid-gestation with a low-lying placenta (LLP) is controversial. We sought to determine the rate of adverse pregnancy outcomes with an initial diagnosis of LLP, and whether this was dependent on a follow up sonographic diagnosis of resolution or the initial placenta-to-internal os distance (P-IOD). Methods: A retrospective cross-sectional study of singleton pregnancies with a sonographically diagnosed LLP between 18-24 weeks' gestation (12/2010 to 7/2018) was conducted at a tertiary referral center in the U.S. Follow-up ultrasound examinations from the late second or early third trimester were reviewed. Maternal morbidity associated with blood loss, regardless of resolution of LLP was recorded and stratified by P-IOD at diagnosis. The LLP was considered resolved if the P-IOD was >= 2.0 cm by 34 weeks' gestation . Proportions of resolution, admissions for antepartum bleeding, preterm delivery, mode of delivery, neonatal morbidity and preterm delivery were obtained. Data was analyzed by comparing categorical variables via Chi-squared test, and continuous variables using Student t-test and analysis of variance (ANOVA). Results: Five hundred three pregnancies met inclusion criteria. All except two LLPs resolved by 34 weeks' gestation (99.6% resolution rate). There were 40 patients who did not have a follow up ultrasound. Overall rates of hemorrhage and blood transfusion were greater than the general population. The rate of maternal hemorrhage between resolved, unresolved, unknown groups, and initial P-IOD was not significantly different. The odds of admission for antepartum bleeding were significantly greater if the P-IOD was <0.5 cm. An increase in neonatal acidosis was found in the group with initial P-IOD <0.5 cm, despite 100% resolution at time of delivery. Conclusions: The diagnosis of an LLP at 18-24 weeks' gestation despite a high rate of resolution, is associated with an increased risk for maternal hemorrhage. LLP may be an independent risk factor for hemorrhage, regardless of the initial P-IOD or resolution. Clinicians and patients should be aware of this risk and prepared to manage adverse events.