Leptin is a predictive marker of pre-eclampsia in obese pregnancies. Increased placental leptin levels in all trimesters of pregnancy represent risk factors for pre-eclampsia. Higher maternal leptin levels increase oxidative stress in high-altitude (HA) residents with pre-eclampsia. Lower serum leptin levels decrease placental production when pre-eclampsia is associated with HIV infection. Lower leptin levels in newborn babies from pre-eclamptic pregnancies are significantly correlated with obesity and oxidative stress. This evidence concerns the gene LEP and HIV infectious disease.