What does “left occiput posterior (LOP)” fetal position mean?

After becoming pregnant, women routinely undergo prenatal examinations at hospitals. However, some fetuses may present with abnormal fetal positioning. What, then, does “left occiput posterior (LOP) position” mean?

What Does “Left Occiput Posterior Position” Mean?

Fetal position refers to the relationship between the presenting part of the fetus and the mother’s pelvis. For example, “left occiput posterior (LOP)” indicates that the fetal occiput (the back of the fetal head) is positioned toward the posterior aspect of the maternal pelvis—i.e., the fetus is facing forward. Under typical circumstances, if the mother has a relatively spacious pelvis and the fetus is not large—for instance, weighing less than 3,500 g—enhanced uterine contractions during labor may facilitate rotation of the fetal head into the left occiput anterior (LOA) position, allowing for spontaneous vaginal delivery.

Generally, the fetal head must pass through the maternal birth canal along its smallest possible diameter, as the birth canal is a bony passage with minimal capacity for expansion. To accommodate the maternal pelvis, the fetal skull undergoes molding—i.e., temporary overlapping of the cranial bones—to reduce the head’s overall diameter and facilitate vaginal delivery. Therefore, if the fetal head is relatively large or the fetus is macrosomic (e.g., weighing over 4,000 g), vaginal delivery in persistent LOP position becomes significantly more difficult and increases the risk of obstructed labor.

Pregnant women should attend regular prenatal check-ups at hospitals. We hope this explanation proves helpful!