A 32-year-old primigravida at 36 weeks of gestation is found to have a breech presentation on routine ultrasound. Which is the most common cause of breech presentation in this patient?

Explanation

## Most Common Cause of Breech Presentation **Key Point:** In the majority of breech presentations at term, no specific cause is identified. This is termed idiopathic breech presentation and accounts for approximately 65–70% of all breech cases. ### Etiology Breakdown | Cause | Frequency | Notes | | --- | --- | --- | | Idiopathic | 65–70% | No identifiable maternal or fetal cause | | Uterine anomalies | 10–15% | Bicornuate, septate, unicornuate uterus | | Placenta previa | 5–10% | Mechanical obstruction to version | | Fetal anomalies | 5–10% | Anencephaly, hydrocephalus, skeletal dysplasia | | Multiparity | Variable | Lax uterine muscles allow abnormal lie | | Prematurity | Variable | Higher rate in preterm deliveries | **High-Yield:** The term "idiopathic breech" does not mean the cause is unknown in a pathological sense—it reflects that the fetus has simply assumed a breech lie without evidence of maternal or fetal pathology. This is the most common scenario encountered in clinical practice. **Clinical Pearl:** Even in idiopathic breech presentation, external cephalic version (ECV) should be offered at 36–37 weeks if there are no contraindications. Success rates are 50–60% in nulliparous women. ### Why Idiopathic Is Most Common - No structural uterine constraint - No placental obstruction - No fetal neurological or skeletal abnormality - Fetus simply maintains breech lie due to chance or minor uterine tone variations **Warning:** Do not assume breech presentation = fetal anomaly. Most breech fetuses are structurally and chromosomally normal.