Placental lactogen, also referred to as chorionic somatomammotropin, is a polypeptide hormone, produced by the placenta during pregnancy. It influences the metabolic processes of both the mother and fetus, aiding in the growth and development of the fetus.^[1] Classified within the somatotropin family, placental lactogen shares both structural and functional similarities to growth hormone and pituitary prolactin.^[2] It has been identified in various mammals, including humans, monkeys, mice, cows, hamster, and sheep.^[3] However, it has not been found in dogs and rabbits.^[2]

The initial placental lactogen-related proteins were identified in rodents^[4] and are commonly categorized into two primary groups based on the timing of their secretion during pregnancy: those occurring during the mid-pregnancy stage, such as placental lactogen-I, and those occurring during the late-pregnancy stage, such as placental lactogen-II.^[3] Similarly, bovine placental lactogen exhibits diversity, through its molecular forms rather than secretion timing, with multiple isoforms differing in molecular weight and charge due to variations in glycosylation and truncated transcripts.^[2] While there are many shared characteristics, placental lactogen is synthesized by distinct trophoblast cell types. In sheep, for example, ovine placental lactogen is generated by binucleate cells.^[5]

• Sibiak, Rafał; Jankowski, Maurycy; Gutaj, Paweł; Mozdziak, Paul; Kempisty, Bartosz; Wender-Ożegowska, Ewa (16 April 2020). "Placental Lactogen as a Marker of Maternal Obesity, Diabetes, and Fetal Growth Abnormalities: Current Knowledge and Clinical Perspectives". Journal of Clinical Medicine. 9 (4): 1142. doi:10.3390/jcm9041142. PMC 7230810. PMID 32316284.