Pregnancy is a complex metabolic state involving dramatic alterations in the hormonal or cytokine environments (increases in estrogen, progesterone, prolactin, cortisol, human chorionic gonadotropin, placental growth hormone and human placental lactogen, TNF-alpha, resistin, leptin, and a decrease in adiponectin) as well as an increasing burden of fuel utilization by the conceptus. Metabolically, the first trimester is characterized by increased insulin sensitivity and lipogenesis. The second and third trimesters, in contrast, are characterized by insulin resistance and increased lipolysis.