Low placenta at the mid trimester anomaly scan-A cause for concern?

Area of Science:

• Obstetrics and Gynecology
• Fetal Medicine
• Diagnostic Imaging

Background:

• Accurate prediction of third-trimester placental location is crucial for managing pregnancy complications.
• Internal os distance (IOD) is a sonographic measurement evaluated in the mid-trimester.
• Understanding factors associated with abnormal placental positioning is essential for clinical practice.

Purpose of the Study:

• To evaluate the predictive accuracy of mid-trimester internal os distance (IOD) for identifying third-trimester low-positioned placentas.
• To establish specific IOD cut-off values for predicting third-trimester placental location.
• To investigate the association of placental site (anterior/posterior) and prior cesarean section history with third-trimester placental position, and to assess maternal and neonatal outcomes.

Main Methods:

• A prospective cohort study included women with low-positioned placentas (IOD < 20 mm) identified during mid-trimester anomaly scans.
• Participants were followed until birth, with third-trimester placental location assessed.
• Relative risks (RR) were calculated for posterior vs. anterior placentas, placenta previa vs. low-lying placenta, and previous cesarean section history. Receiver operating characteristic (ROC) curves and likelihood ratios were used to determine IOD cut-offs.

Main Results:

• A significantly higher risk of third-trimester low-positioned placenta was observed in women with posterior placentas (9.28% vs. 0.74%, RR 1.45) compared to anterior placentas.
• Women with placenta previa showed a substantially higher risk (68.57% vs. 1.69%, RR 6.51) than those with low-lying placentas.
• A history of cesarean section also correlated with an increased risk (9.41% vs. 5.87%, RR 1.47).

Conclusions:

• The majority of placentas identified as low-positioned in the mid-trimester (93.42%) were normally situated by the third trimester.
• Specific IOD cut-off values were identified: -40 mm for anterior placentas and 14.3 mm for posterior placentas.
• IOD measurement shows promise as a tool for predicting third-trimester placental position, aiding in risk assessment and management.