Low Birth Weight: Maternal, Fetal & Environmental Risk Factors

Low birth weight (LBW), defined as <2,500 g at term, arises from a complex interplay of maternal, fetal, placental, and environmental factors.

Maternal Factors

• Age: <18 or >35 years
• Nutritional status: Low pre‑pregnancy BMI, inadequate gestational weight gain
• Medical conditions: Chronic hypertension, preeclampsia/eclampsia, diabetes (pregestational or gestational), renal/heart/thyroid disease
• Obstetric history: Short interpregnancy interval (<18 months), multiple gestation, prior LBW/preterm infant
• Substance use: Smoking (major modifiable risk), alcohol, illicit drugs
• Infections: UTI, STIs, periodontal disease, malaria, COVID‑19
• Psychosocial: High stress, depression, intimate partner violence, low socioeconomic status

Fetal & Placental Factors

• Preterm birth: Leading cause of LBW (immaturity)
• Intrauterine growth restriction (IUGR): Placental insufficiency, genetic syndromes, congenital anomalies, infections (TORCH)
• Chromosomal abnormalities: Trisomies 13, 18, 21; Turner syndrome

Environmental & Systemic Factors

• Air pollution (PM2.5), lead, mercury, pesticides
• High altitude (>2,500 m)
• Lack of prenatal care (missed screening, untreated conditions)
• Food insecurity, poor housing

Prevention & Mitigation

• Preconception care: optimize health, folic acid, smoking cessation
• Early, regular prenatal visits
• Manage chronic diseases before/during pregnancy
• Nutritional support (WIC, supplementation)
• Screen/treat infections
• Progesterone for prior preterm birth; aspirin for preeclampsia risk

Long‑Term Implications

LBW increases risk of neonatal mortality, neurodevelopmental delays, metabolic syndrome, cardiovascular disease, and obesity in adulthood (Barker hypothesis). Early intervention improves trajectories.