human placental lactogen

Human placental lactogen is the placenta's way of nudging the mother's metabolism to feed two. Picture it telling the mother's body: “use fat for your own energy, and leave the sugar in the blood for the baby.” It quietly reshapes how she handles nutrients across the second half of pregnancy.

Structurally it resembles both growth hormone and prolactin, and it rises in proportion to placental mass. Its key action is to make maternal tissues somewhat resistant to insulin, so blood glucose stays higher and is shunted toward the fetus. At the same time it promotes the breakdown of maternal fat stores, freeing fatty acids as an alternative fuel for the mother.

These same insulin-resistant effects explain why pregnancy can unmask a tendency toward high blood sugar. When the mother's pancreas cannot keep up with the extra insulin demand, gestational diabetes can result, and human placental lactogen is one of the hormones driving that physiological strain.

A caveat: despite its name, human placental lactogen plays only a minor role in actual milk production compared with prolactin. Its primary importance is metabolic, and its levels are not routinely measured clinically because they vary widely and add little to modern pregnancy monitoring.