How Your Placenta Makes and Releases the Peptide Hormones That Keep Pregnancy on Track

What the researchers found

The placenta functions as a temporary endocrine organ producing multiple peptide hormones — including human chorionic gonadotropin (hCG), human placental lactogen (hPL), and placental growth hormone (hPGH) — that are essential for maintaining pregnancy, supporting fetal growth, and driving metabolic adaptations in the mother. Dysregulation of these hormones is linked to pregnancy complications.

The review highlights that despite decades of research, how these hormones are processed and secreted within the placenta's unique syncytiotrophoblast structure remains poorly understood. The interplay between constitutive (continuous) and regulated (on-demand) secretion pathways adds complexity. Emerging 2D and 3D placental models are beginning to provide new insights into these trafficking mechanisms.

Why it matters

Pregnancy complications like preeclampsia, gestational diabetes, and intrauterine growth restriction are often tied to disrupted placental hormone levels. Understanding exactly how the placenta produces and releases its peptide hormones could reveal new diagnostic markers for at-risk pregnancies and potential therapeutic targets. The placenta is essentially a hormone factory that we still don't fully understand at the cellular level.

The numbers in context

hCG + hPL + hPGH + other peptide hormones · constitutive and regulated secretion · syncytiotrophoblast structure

How the study worked

Review synthesizing current knowledge on intracellular trafficking and secretion pathways of placental peptide hormones, including discussion of 2D and 3D placental models and advanced protein trafficking assays as emerging research tools.

Who was studied

Not applicable — review of placental peptide hormone biology relevant to all pregnancies

What this study cannot tell us

As a review, it identifies knowledge gaps rather than filling them with new data. The unique structure of the syncytiotrophoblast makes placental hormone secretion difficult to study, and many findings come from simplified cell culture models that may not fully recapitulate in-vivo placental physiology. Human placental tissue access is limited to delivery timepoints.

How to read the evidence

This is a comprehensive review published in Frontiers in Endocrinology that synthesizes current knowledge and identifies research gaps. It provides a solid overview of the field but primarily highlights what is not yet understood about placental hormone trafficking.

When this study was published

Published in 2025 in Frontiers in Endocrinology. Very current, capturing the latest advances in placental biology including emerging 3D model technologies.

The bigger picture

Placental peptide hormones are among the most clinically important peptides in medicine — hCG is the basis of every pregnancy test, and placental hormone levels are used to screen for pregnancy complications. Yet the basic cell biology of how these hormones are made and released is still being worked out. New 3D placental organoid models may finally crack open the black box of placental secretion, potentially leading to better prediction and prevention of complications that affect millions of pregnancies each year.

Questions still open

• Can placental organoid models accurately reproduce the hormone secretion patterns seen in human pregnancy?
• Which specific secretory pathway disruptions are most strongly linked to preeclampsia and gestational diabetes?
• Could targeted interventions to restore normal placental peptide hormone secretion prevent pregnancy complications?

Common questions

Read the original research

Secretion of placental peptide hormones: functions and trafficking.

Frontiers in endocrinology, 16, 1584303

Citation

Ahmadi, Sadia M; Perez, Maira L; Guardia, Carlos M. (2025). Secretion of placental peptide hormones: functions and trafficking.. Frontiers in endocrinology, 16, 1584303. https://doi.org/10.3389/fendo.2025.1584303