Clinical counterpoint: the physiology of placental lactogen in human pregnancy.

In summary, current evidence strongly suggests that PL may play a pivotal role during pregnancy, acting through distinct PL receptors to regulate and coordinate growth and metabolism in the mother and fetus. In early and midgestation, PL may be secreted preferentially into the fetal circulation, exerting growth-promoting effects at a time when the rate of linear growth of the fetus is maximal. Subsequently, during the latter half of pregnancy, the metabolic actions of PL in the mother and fetus may predominate, ensuring the optimal supply of nutrients to the fetus and utilization of the nutrients by fetal tissues. It therefore appears that PL affects fetal growth both by exerting effects on the fetus and the mother. Although hPL acts as "growth hormone of pregnancy," the regulation of the synthesis and secretion of hPL appears to be markedly different than that of GH.