A 28-year-old G2P1 at 34 weeks of gestation is found to have transverse lie on routine ultrasound. She has no prior history of uterine surgery or structural abnormality. Which is the most common cause of transverse lie in this clinical scenario?

Explanation

## Most Common Cause of Transverse Lie **Key Point:** Multiparity with lax uterine muscles is the most common cause of transverse lie, particularly in multiparous women. ### Etiology of Transverse Lie | Cause | Frequency | Clinical Context | |-------|-----------|------------------| | Multiparity (lax uterus) | 40–50% | Most common; occurs in multiparous women with reduced uterine tone | | Placenta previa | 15–20% | Placental implantation in lower segment restricts normal rotation | | Uterine anomalies/fibroids | 10–15% | Structural distortion of uterine cavity | | Fetal anomalies | 5–10% | Anencephaly, skeletal dysplasias | | Polyhydramnios | 5% | Excess fluid reduces fetal constraint | | Idiopathic | 10–15% | No identifiable cause | **High-Yield:** Transverse lie occurs in approximately 0.3% of term pregnancies. The incidence is significantly higher in multiparous women (up to 1–2%) due to progressive loss of uterine muscle tone with each pregnancy. ### Mechanism in Multiparity 1. Repeated pregnancies cause progressive stretching and weakening of uterine myometrium 2. Reduced uterine muscle tone fails to maintain normal fetal alignment 3. Fetus adopts transverse lie due to lack of constraint 4. Risk increases with parity: G3+ > G2 > G1 **Clinical Pearl:** A multiparous woman presenting with transverse lie in the absence of placenta previa or structural anomalies should raise suspicion for multiparity-related uterine laxity. This is the single most common scenario in clinical practice. **Mnemonic:** **FLAP** — Factors causing transverse lie: - **F**ibroids (uterine) - **L**ax uterus (multiparity) - **A**nomalies (fetal or uterine) - **P**lacenta previa **Warning:** Do not automatically assume placenta previa in every transverse lie — obtain detailed ultrasound assessment of placental location. Many multiparous women with transverse lie have normally-positioned placentas. [cite:Obstetric and Gynaecological Society of India Guidelines on Malpresentation]