HPL

Human placental lactogen (hPL) is a placental peptide hormone produced by the syncytiotrophoblasts of the human placenta during pregnancy. It is a member of the growth hormone/prolactin family and is also referred to as human chorionic somatomammotropin (hCS). hPL plays a key role in preparing the maternal body to support fetal development.

Biochemically, hPL is a single-chain polypeptide of about 22 kilodaltons, encoded by members of the placental gene cluster on chromosome 17, including the CSH1 and CSH2 genes. The placenta expresses multiple related transcripts, producing several variants of placental lactogen throughout gestation. Secretion of hPL increases as pregnancy progresses and placental mass expands.

The physiological role of hPL is primarily to modulate maternal metabolism to favor fetal nutrient supply. It induces changes in carbohydrate and lipid metabolism that increase maternal lipolysis and insulin resistance, thereby elevating circulating free fatty acids and ensuring greater glucose availability for the fetus. In addition to metabolic effects, hPL has growth-promoting properties and contributes to mammary gland development in preparation for lactation, though lactation is mainly regulated by other hormones after birth.

Regulation and clinical relevance: hPL production correlates with placental size and gestational age, and its expression is influenced by placental hormones and maternal nutritional status. Routine clinical measurement of hPL is not part of standard prenatal screening, but it may be assessed in research settings or in evaluations of placental function. Abnormal hPL levels have been linked to placental dysfunction and may be associated with metabolic or fetal growth disturbances in some pregnancies.