During a neonatal screening program in New Delhi, 50 infants with developmental dysplasia of the hip (DDH) are identified. Which is the most common demographic characteristic among these infants?

Explanation

## Most Common Demographic Profile in DDH **Key Point:** Female infants with vaginal delivery represent the most common demographic group affected by developmental dysplasia of the hip, due to the combined effect of female sex (hormonal laxity) and vaginal delivery (intrauterine positioning). ### Sex Distribution in DDH | Sex | Prevalence | Relative Risk | | --- | --- | --- | | Female | 80–90% of all cases | 4–8× higher than males | | Male | 10–20% of all cases | Baseline | **High-Yield:** Females are affected 4–8 times more frequently than males. This is due to: - Greater ligamentous laxity in females (estrogen-mediated) - Maternal hormones (relaxin) causing increased capsular laxity - Anatomical predisposition ### Delivery Mode and DDH Risk | Delivery Mode | DDH Risk | Mechanism | | --- | --- | --- | | Vaginal (vertex) | Baseline to slightly increased | Intrauterine positioning (hip flexion, adduction) | | Breech | 10–25× increased | Prolonged hip extension and external rotation in utero | | Cesarean section | Slightly decreased | Avoidance of intrauterine compression | **Clinical Pearl:** While breech presentation is a strong risk factor (10–25× increased risk), it occurs in only ~3% of deliveries. Therefore, in absolute numbers, **most cases of DDH occur in vaginally-delivered infants** because vaginal delivery is far more common (>95% of deliveries). ### Prevalence by Demographics **Mnemonic:** **FVBF** — Females, Vaginal delivery, Breech (risk factor), Family history - **Most common:** Female + Vaginal delivery (majority of DDH cases) - **Highest risk:** Female + Breech presentation (but rarer in absolute numbers) - **Least common:** Male + any delivery mode ### Why This Matters Clinically **High-Yield:** Universal screening (clinical examination + ultrasound in high-risk groups) is recommended for all infants, but especially: - All females - All breech-presented infants - Infants with positive family history - First-born infants