What Is Placental Lactogen? Definition and What Research Reports
Placental lactogen is a single-chain polypeptide hormone made by the placenta and belonging to the growth hormone/prolactin family. In humans it is often abbreviated hPL or called chorionic somatomammotropin. In the literature it appears mainly as a pregnancy biomarker and as a source of smaller cleavage fragments. Published work has reported hPL-derived vasoinhibin in placental tissue, associations between maternal hPL concentrations and pregnancy outcomes, and changes in placental lactogen in animal models. This glossary entry is definitional only.
Definition
Placental lactogen is a polypeptide hormone secreted by the placenta during pregnancy. In humans it is usually written as human placental lactogen (hPL) and is also called chorionic somatomammotropin (CSH). It is a single-chain protein hormone that belongs to the growth hormone (GH) and prolactin (PRL) family, meaning it shares substantial sequence and structural similarity with pituitary growth hormone and with prolactin and signals through related receptor systems. It is produced principally by the syncytiotrophoblast — the outer cell layer of the placenta that faces maternal blood — and is released into the maternal circulation, where its concentration generally rises as the placenta grows across gestation. Because it is made by the placenta rather than a maternal endocrine gland, placental lactogen is treated in the literature as a placenta-derived marker of placental mass and function, and is measured in maternal serum rather than administered.
What Class of Molecule It Is
Placental lactogen is a protein hormone, not a small molecule and not a steroid. Its size places it above what is usually meant by "peptide" in a research-chemical sense — it is a full-length polypeptide hormone in the somatotropin family. That family relationship is the reason the same analytical language (lactogenic activity, somatotropic activity, receptor cross-reactivity with prolactin and growth hormone receptors) recurs across papers on prolactin, placental growth hormone and placental lactogen.
Placental lactogen is also a precursor in the literature. Researchers reported that human placental tissue contains a placental lactogen-derived vasoinhibin, a smaller fragment produced by cleavage of the parent hormone (PMID 35265784). A separate group reported that plasmin cleaves both prolactin and placental lactogen to generate vasoinhibin-like peptides, identifying an enzymatic route by which the intact hormone is converted into shorter bioactive fragments (PMID 34601001). This precursor-to-fragment relationship is the main reason placental lactogen appears in peptide-focused literature at all.
Where the Term Appears in Research
Three usages dominate the published record:
- As a maternal serum biomarker. Concentrations are measured in maternal blood and correlated with pregnancy outcomes, screening results, behaviour or nutrition.
- As a fragment precursor. Work on vasoinhibins treats placental lactogen alongside prolactin as a substrate for proteolytic cleavage (PMID 34601001).
- As a comparative endocrinology term. Non-human placental lactogens — ovine, bovine, rodent, cetacean — are studied in their own right, so the term is not exclusive to humans.
Related Terms
| Term | What it refers to |
|---|---|
| Human placental lactogen (hPL) | The placenta-derived member of the GH/PRL family measured in maternal serum |
| Chorionic somatomammotropin (CSH) | Alternative name for the same hormone, reflecting its somatotropic and mammotropic similarity |
| Prolactin (PRL) | Pituitary hormone in the same family; reported as a plasmin substrate alongside placental lactogen (PMID 34601001) |
| Placental growth hormone | A separate placenta-expressed GH variant measured alongside prolactin and placental lactogen in maternal cohorts (PMID 37049394) |
| Vasoinhibin | Shorter cleavage fragment; a placental lactogen-derived form was reported in human placental tissue (PMID 35265784) |
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Fragment Biology
The 2022 report in the Journal of the Endocrine Society described the identification of a vasoinhibin derived from placental lactogen within human placental tissue, extending vasoinhibin biology beyond prolactin as the sole precursor (PMID 35265784). A 2021 paper in Molecular and Cellular Endocrinology reported that the protease plasmin generated vasoinhibin-like peptides by cleaving both prolactin and placental lactogen, characterising the cleavage chemistry rather than testing any therapeutic use (PMID 34601001).
Maternal Serum Measurement and Pregnancy Outcomes
Placental lactogen has been examined as a screening analyte: a 2007 study in Prenatal Diagnosis reported that human placental lactogen functioned as a first-trimester maternal serum marker associated with Down syndrome (PMID 17154235). Another study examined fetoplacental complex hormones in pregnant women with miscarriage and reported changes in hormone levels in that group relative to comparison pregnancies (PMID 34621371).
Researchers have also correlated maternal placental lactogen with maternal factors. A 2022 Frontiers in Endocrinology analysis examined prenatal health behaviours as predictors of human placental lactogen levels (PMID 36157466). A 2023 Nutrients paper drawing on two prospective pregnancy cohorts reported changes in maternal prolactin, placental lactogen and placental growth hormone in the context of elevated maternal folate status following folic acid food fortification (PMID 37049394). A 2020 Psychoneuroendocrinology study reported that low serum placental lactogen at term was associated with postnatal symptoms of depression and anxiety among women delivering female infants (PMID 32247203). These are observational associations reported in the cited papers, not demonstrations of cause and effect.
Tissue Expression
Expression is not limited to the placenta in the descriptive literature: a 2023 Cureus report described the pattern of human placental lactogen expression across normal, lactational and malignant mammary epithelium (PMID 36945262).
Animal and Comparative Studies
Rodent work has used placental lactogen as a readout of placental endocrine function. An Endocrinology study reported that maternal hypothyroidism in rats reduced placental lactogen, lowered insulin levels and caused glucose intolerance (PMID 34791119). A 2023 toxicology study examined the effects of melamine and cyanuric acid on placental and fetal development in rats (PMID 37247804).
In livestock and wildlife endocrinology, a longitudinal ultrasonographic study in sheep assessed placentome diameter alongside maternal ovine placental lactogen across gestation (PMID 41640854). A veterinary study localised peptide hormones in the placentas of Bryde's, sei and common minke whales, extending placental hormone description to cetaceans (PMID 38417877).
Scope and Limits of the Evidence: What Studies Report
The published work summarised above is largely observational, descriptive or preclinical. Human papers measured endogenous placental lactogen concentrations in maternal serum and related them to screening outcomes, behaviours, nutrition status or postnatal mood symptoms (PMID 17154235, PMID 32247203). Animal papers reported changes in placental lactogen as a consequence of an experimental condition such as maternal hypothyroidism, rather than as an intervention (PMID 34791119). None of the verified literature cited here evaluated administration of placental lactogen or a placental lactogen fragment to humans, and no human dosing regimen appears in these reports. Associations described in observational cohorts can be confounded by gestational age, placental mass, assay method and maternal health status, and the authors of such studies typically frame findings as correlations requiring further work.
This page is for educational purposes only and is not medical advice; consult a licensed physician about any medical question, pregnancy-related concern, or laboratory result. Placental lactogen is an endogenous hormone measured in clinical and research settings; it is not described in the cited literature as a consumer product, and nothing here describes use of any substance.
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- Human Placental Tissue Contains A Placental Lactogen-Derived Vasoinhibin (Journal of the Endocrine Society, 2022)
- Plasmin generates vasoinhibin-like peptides by cleaving prolactin and placental lactogen (Molecular and Cellular Endocrinology, 2021)
- Prenatal health behaviours as predictors of human placental lactogen levels (Frontiers in Endocrinology, 2022)
- Changes in the level of fetoplacental complex hormones in pregnant women with miscarriage (Journal of Medicine and Life, 2021)
- Maternal Hypothyroidism in Rats Reduces Placental Lactogen, Lowers Insulin Levels, and Causes Glucose Intolerance (Endocrinology, 2022)
- The Pattern of Expression of Human Placental Lactogen Across Normal, Lactational, and Malignant Mammary Epithelium (Cureus, 2023)
- Human placental lactogen is a first-trimester maternal serum marker of Down syndrome (Prenatal Diagnosis, 2007)
- Low serum placental lactogen at term is associated with postnatal symptoms of depression and anxiety in women delivering female infants (Psychoneuroendocrinology, 2020)
- Elevated Maternal Folate Status and Changes in Maternal Prolactin, Placental Lactogen and Placental Growth Hormone Following Folic Acid Food Fortification (Nutrients, 2023)
- Longitudinal ultrasonographic assessment of placentome diameter and maternal ovine placental lactogen across gestation in sheep (Frontiers in Veterinary Science, 2026)
- Localization of peptide hormones in the placentas of Bryde's, sei, and common minke whales (Journal of Veterinary Medical Science, 2024)
- Effects of melamine and cyanuric acid on placental and fetal development in rats (Food and Chemical Toxicology, 2023)
Frequently asked questions
Is placental lactogen a peptide or a protein hormone?▾
It is a single-chain polypeptide hormone in the growth hormone and prolactin family, larger than what is usually meant by a short research peptide. It enters peptide-focused discussion mainly because it can be cleaved into smaller fragments: researchers reported that plasmin generates vasoinhibin-like peptides from both prolactin and placental lactogen (PMID 34601001).
Where does placental lactogen come from?▾
It is produced by the placenta — specifically the syncytiotrophoblast — and released into the maternal circulation during pregnancy, which is why it is measured in maternal serum. Descriptive work has also reported placental lactogen expression patterns across normal, lactational and malignant mammary epithelium (PMID 36945262), and localisation of placental peptide hormones in cetacean placentas (PMID 38417877).
What is a placental lactogen-derived vasoinhibin?▾
A vasoinhibin is a shorter fragment generated by cleavage of a parent hormone. A 2022 report described a placental lactogen-derived vasoinhibin present in human placental tissue (PMID 35265784), and a separate paper reported that the protease plasmin cleaved prolactin and placental lactogen to produce vasoinhibin-like peptides (PMID 34601001). Both papers characterised the chemistry rather than any therapeutic application.
Why is placental lactogen measured in pregnancy research?▾
It is used as a serum marker reflecting placental output. A 2007 study reported human placental lactogen as a first-trimester maternal serum marker associated with Down syndrome (PMID 17154235), and another study examined fetoplacental complex hormone levels in pregnant women with miscarriage (PMID 34621371). These were measurement studies, not interventions.
Do maternal factors influence reported placental lactogen levels?▾
Published cohorts have examined that question. One analysis looked at prenatal health behaviours as predictors of human placental lactogen levels (PMID 36157466), and a 2023 study of two prospective pregnancy cohorts reported changes in maternal prolactin, placental lactogen and placental growth hormone in relation to elevated maternal folate status after folic acid food fortification (PMID 37049394). These are associations, not proven causes.
What have animal studies reported about placental lactogen?▾
An Endocrinology study reported that maternal hypothyroidism in rats reduced placental lactogen, lowered insulin levels and caused glucose intolerance (PMID 34791119). A sheep study longitudinally assessed placentome diameter alongside maternal ovine placental lactogen across gestation (PMID 41640854). A separate rat study examined the effects of melamine and cyanuric acid on placental and fetal development (PMID 37247804).
Has placental lactogen been given to people in the cited literature?▾
No. The verified papers summarised on this page measured endogenous placental lactogen in humans or animals, or characterised its cleavage fragments in tissue and in vitro; none described administering placental lactogen to humans, and none reported a human dosing regimen. Reported human findings, such as the association between low term placental lactogen and postnatal mood symptoms (PMID 32247203), are observational.
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References
This page summarises published research for education — it is not medical advice, and nothing here is a recommendation to use, purchase, or dose any substance. Study parameters described are what researchers reported, not instructions. Consult a qualified clinician before any health decision.