Maternal BMI and Diet Quality Modulate Pregnancy Oxidative and Inflammatory Homeostasis

<b>Background/Objectives:</b> Maternal nutrition and pregestational BMI are critical determinants of pregnancy outcomes. This prospective multicenter observational study investigated the interplay between prepregnancy BMI, dietary patterns, and oxidative/inflammatory status in 153 Italian healthy pregnant women with normal weight (NW), overweight (OW), or obesity (OB). <b>Methods:</b> Detailed clinical, biochemical, placental, and neonatal data were measured at third trimester and delivery. Dietary intake was assessed via a validated questionnaire, and dietary patterns were derived using principal component analysis. <b>Results:</b> OW and OB women had significantly higher levels of inflammatory (CRP, hepcidin) and oxidative stress biomarkers (DNA/RNA damage, catalase activity) than NW. Multivariate models confirmed independent associations between BMI and these biomarkers (CRP: β = 0.297, <i>p</i> = 0.000; hepcidin: β = 1.419, <i>p</i> = 0.006; DNA/RNA damage: β = 409.9, <i>p</i> = 0.000; catalase activity: β = 1.536, <i>p</i> = 0.000). Superoxide dismutase activity and total antioxidant capacity were not associated with BMI. Nutritional intake across BMI groups was largely suboptimal relative to national recommendations, with insufficient levels of polyunsaturated fats and key micronutrients. Four dietary patterns were identified, with adherence varying by BMI. A "prudent-style" pattern (high plant, low animal) was positively associated with gestational age (β = 0.243, <i>p</i> = 0.033) and inversely with neonatal head circumference (β = -0.414, <i>p</i> = 0.050). A "Western-like" pattern (high sugars, snacks, animal fats) was linked to reduced maternal ferritin (β = -2.093, <i>p</i> = 0.036) and increased neonatal head circumference (β = 0.403, <i>p</i> = 0.036). However, not all deviations from the "prudent-style" pattern were metabolically equivalent: while Pattern 3 (high-protein, carbohydrate) may offer partial protective effects, Pattern 4 (moderate protein/plant/sugar) displayed elements of nutritional imbalance with signs of placental inefficiency (β = -0.384, <i>p</i> = 0.023). <b>Conclusions:</b> These findings underscore the dual impact of maternal BMI and diet quality on oxidative-inflammatory balance and perinatal outcomes, supporting the need for early, individualized nutritional strategies in pregnancy. This is further emphasized by the variability in dietary adherence across BMI categories.