Among women presenting with antepartum haemorrhage due to placenta previa, which is the most common maternal risk factor associated with its development?

Explanation

## Risk Factors for Placenta Previa **Key Point:** Multiparity and previous uterine instrumentation (curettage, dilation and evacuation) are the most common maternal risk factors for placenta previa. ### Major Risk Factors — Frequency and Mechanism | Risk Factor | Relative Risk | Mechanism | |-------------|---------------|----------| | **Multiparity + prior curettage** | **Highest** | Endometrial damage → abnormal placentation in lower segment | | Advanced maternal age (>35 y) | Moderate | Associated with multiparity; independent effect modest | | Maternal smoking | Moderate | Impaired endometrial vascularization; hypoxia-induced placental compensation | | Cocaine use | Moderate | Vasoconstrictive effect; placental ischaemia | | Prior caesarean delivery | Moderate | Uterine scar; abnormal placentation | | Intrauterine growth restriction | Weak | Consequence, not cause; poor placental function | | Assisted reproductive technology | Moderate | Endometrial factors; embryo implantation site | ### Why Multiparity + Curettage is Most Common **High-Yield:** Multiparity is the single most prevalent risk factor in the general obstetric population. Combined with a history of curettage (D&C for miscarriage, abortion, or retained products), the risk increases substantially because: 1. Repeated pregnancies expose the endometrium to placentation cycles 2. Curettage causes endometrial scarring and loss of normal decidualization 3. The lower uterine segment has thinner endometrium, making it more vulnerable to abnormal implantation after trauma **Clinical Pearl:** A multiparous woman with a history of one or more curettage procedures has a cumulative risk that exceeds that of advanced maternal age alone. This is why detailed obstetric and gynaecological history is essential in risk stratification. ### Distinction: Risk Factor vs. Consequence **Warning:** Intrauterine growth restriction (IUGR) is often *associated* with placenta previa but is a *consequence* of poor placental function, not a cause. IUGR does not increase the risk of developing previa; rather, previa may lead to IUGR if placental insufficiency develops.