The objectives of this thesis were to understand how maternal underweight, obesity and preterm birth alter placental development and function. Placental pathology data were obtained from an archived dataset, and qPCR and immunohistochemistry were used in a current cohort, to explore the effects of maternal body mass index (BMI) and/or preterm birth on placental development and function. Increased maternal BMI associated with increased placental inflammation, maternal vascular malperfusion, and decreased placental efficiency. Preterm placentae had increased expression of multidrug resistance transporters, and altered expression of antimicrobial peptides. These findings revealed maternal underweight and obesity are not inert conditions for the developing placenta. Upregulated placental efflux transport earlier in gestation may regulate fetal exposure to increased inflammation/infection at preterm, while altered placental defences may impair placental-mediated fetal protection. Understanding placental adaptations in these common conditions helps to uncover the mechanisms linking suboptimal maternal BMI and inflammatory states with adverse pregnancy outcomes.