Abstract: Background: Placenta previa and low-lying placenta are potentially fatal conditions for both mother and child. The purpose of this work was to evaluate the cut-off level distance between lower edge of placenta and internal cervical os and whether it can predict third trimester placenta previa or not.
Methods: This prospective observational work was carried out on 50 low- lying placenta cases with single living pregnancy with 18–24-week gestation. Patients were splitted into two groups: group 1 consists of 46 individuals; group 2 consists of 4 individuals. They were recruited from Obstetrics and Gynecology departments at Tanta University Hospitals and Kafr El–Sheikh General hospital.
Results: Second-trimester internal os distance (IOD) associated significantly with placental position in the third trimester also when considering those with an anteriorly and posteriorly located placenta, IOD values of at least 5 mm for posteriorly and at least 2 mm for anterior located placenta had a likelihood ratio of 0.1 and 0 respectively in the prediction of an abnormally positioned placenta in the third trimester. All women with an IOD at or above these cut-off values can be reassured without follow-up that their final placental position will be normal. Regarding IOD; AUC was 0.937, 0.850 the sensitivity was 93%, 92% & the specificity was 57%, 64% Anterior and posterior respectively.
Conclusions: IOD cut-off value of 5mm or less was highly sensitive in predicting placenta previa in third trimester.
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