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Ultrasound/Imaging

Poster Session 4

(1122) Revisiting low-lying placenta: internal os distance and pregnancy outcomes

Wednesday, February 14, 2024
1:00 PM – 2:30 PM  
Location: Prince George's Exhibit Hall CDE, Lower Atrium Level
Objective: Low-lying placenta is diagnosed when the internal os distance (IOD) is 2 centimeters or less without any part covering the os and has been associated with antepartum and postpartum hemorrhage, hospitalization, cesarean delivery and small for gestational age neonates. The management of a low-lying placenta remains undefined. A recent study suggested using >5 mm as a cutoff for trial of labor. We sought to report outcomes associated with this cutoff.  

Study Design:

Pregnant people diagnosed with placenta previa or low-lying placenta in the second trimester who underwent a follow-up examination in the third trimester and delivered at our institution between January 2012 and March 2023 were included. The last scan with an IOD on transvaginal imaging prior to delivery was used. Outcomes were grouped based on IOD as 0-5, 6-20, and >20 mm. Maternal and neonatal outcomes were collected from an available obstetric database and electronic chart review. Patients with placenta previa, other placental abnormalities (e.g. placenta accreta spectrum) or cord abnormalities near the cervix (e.g. vasa previa) were excluded from the analysis. Statistical analysis included χ2 for categorical measures and ANOVA for continuous measures, with P < 0.05 considered significant.

Results: A total of 344 patients met inclusion criteria for analysis. Third trimester follow-up sonography was performed at a mean gestational age of 33.5±2.0 weeks. Maternal age was significantly different between groups but not race/ethnicity, BMI, or parity (Table). Compared to normal implantation, a low-lying placenta was delivered at a lower relative gestational age; had increased rates of antepartum hemorrhage, hospitalization, and cesarean; and a decreased induction rate. No differences were observed for small for gestational age, postpartum hemorrhage, or maternal transfusion.

Conclusion: Low-lying placenta at < 5 and 6-20 mm demonstrated increased pregnancy morbidity. Patients attempting trial of labor should be counseled on these risks and shared decision making pursued.