A 32-year-old primigravida at 28 weeks of gestation presents with vaginal bleeding and uterine contractions. Fetal heart rate is 140 bpm and reactive. Cervical examination reveals 2 cm dilatation and 50% effacement. Which of the following is NOT a recognized risk factor for preterm labor in this patient?

Explanation

## Risk Factors for Preterm Labor: Comprehensive Review ### Maternal Age and Preterm Labor **Key Point:** Advanced maternal age (≥35 years) is NOT a recognized independent risk factor for spontaneous preterm labor. While advanced maternal age increases risks for chromosomal abnormalities and gestational diabetes, it does not directly increase the risk of preterm delivery in the absence of comorbidities. ### Established Risk Factors for Preterm Labor | Risk Factor Category | Examples | Mechanism | |---|---|---| | **Placental causes** | Placenta previa, placental abruption, placental insufficiency | Abnormal placentation, bleeding, uterine irritability | | **Infection/Inflammation** | Bacterial vaginosis, UTI, chorioamnionitis, periodontal disease | Ascending infection, inflammatory cascade, prostaglandin release | | **Uterine overdistension** | Polyhydramnios, multiple gestation | Mechanical stretch, increased uterine irritability | | **Uterine anomalies** | Bicornuate uterus, uterine septum, incompetent cervix | Structural inability to maintain pregnancy | | **Maternal factors** | Smoking, substance abuse, poor nutrition, low BMI | Placental dysfunction, immunosuppression | | **Obstetric history** | Previous preterm birth, recurrent miscarriage | Cervical insufficiency, uterine pathology | | **Maternal age** | **< 17 years or > 40 years** (extremes only) | Biological immaturity or age-related comorbidities | **High-Yield:** The relationship between maternal age and preterm labor is U-shaped — very young mothers (< 17) and very advanced age (> 40) carry increased risk, but age 35 alone is NOT an independent risk factor. ### Why the Other Options Are Correct Risk Factors **Placenta Previa:** - Presents with painless vaginal bleeding - Causes uterine irritability and contractions - Associated with preterm labor in 20–30% of cases **Bacterial Vaginosis:** - Increases preterm labor risk 1.5–3 fold - Mechanism: ascending infection, inflammatory cytokine release, prostaglandin production - Screening and treatment in symptomatic pregnant women is recommended **Polyhydramnios:** - Excessive amniotic fluid causes overdistension - Increases intrauterine pressure and uterine irritability - Associated with preterm labor, especially in severe cases (AFI > 25 cm) **Clinical Pearl:** In this case, the patient has placenta previa (vaginal bleeding at 28 weeks) and is at genuine risk for preterm labor. Maternal age 32 is not a risk factor by itself; the risk is driven by the placental pathology and uterine irritability. **Mnemonic for Preterm Labor Risk Factors — INFECTION, PLACENTA, UTERINE:** - **I** — Infection (BV, UTI, chorioamnionitis) - **N** — Nutritional deficiency, Nulliparity - **F** — Fetal anomalies, Fever - **E** — Extremes of maternal age (< 17 or > 40) - **C** — Cervical insufficiency, Cigarette smoking - **T** — Twin/multiple gestation - **I** — Intrauterine bleeding (abruption, previa) - **O** — Overdistension (polyhydramnios) - **N** — Neoplasia (uterine fibroids) **Warning:** Do not confuse advanced maternal age (≥35) with preterm labor risk. Age 35 is a threshold for Down syndrome screening, NOT for preterm labor.