(892) Time to Resolution of Low Lying Placentas

Most pregnant women who have a 2^nd-trimester ultrasound (US) also undergo trans-vaginal US to determine cervical length. A low-lying placenta (edge measuring ≤2cm from the cervix) is a frequent finding. Although most low-lying placentas will resolve by term, there is limited information on the time to resolution. The objective of this study was to determine the timeline to resolution of a low-lying placenta and the optimal timing of follow-up US examinations.

Study Design: IRB approved retrospective cohort study of singleton pregnancies who had a trans-vaginal US between 16-6/7 to 24-0/7 weeks gestation from 1/2019-12/2022. Potential subjects were identified by querying the US database for ICD-10 code O44.42. Patients were included if they had follow-up transvaginal scans until resolution (placental edge >2cm from the cervix) or within 4 weeks of delivery. Patients were excluded if their low lying placenta resolved before 20 weeks. The proportion of resolved low-lying placentas at weekly intervals and mean and median weeks to resolution were calculated.

Results:

626 patients were identified, of which 350 patients met inclusion criteria. Three (3) patients had an unresolved low lying placenta by time of delivery, leaving 347 patients with a resolved low lying placenta (99.14%). The mean (± SD) gestational age at diagnosis was 20-3/7 (±1-5/7) weeks. The mean (± SD) time to resolution was 6-3/7 (± 3-2/7) weeks. The median time to resolution was 5-1/7 weeks (range 1-1/7 to 19-0/7 weeks). A survival curve analysis was performed demonstrating that over 60% of low lying placentas had resolved by 26 weeks gestation and 88% had resolved by 30 weeks.

Conclusion: The vast majority of low-lying placentas diagnosed in the second trimester resolve by 30 weeks gestation. This information may help alleviate patient anxiety and direct optimal timing of follow-up US examinations.