How the Fetus and Mother Independently Handle Heart-Protecting Natriuretic Peptides | Research

The takeaway

The fetus and mother produce and metabolize natriuretic peptides (ANP and BNP) completely independently, with the placenta actively degrading fetal ANP while BNP survives in precursor forms.

Independent systems
No correlation between maternal and fetal natriuretic peptide levels — the placenta forms a complete barrier between the two circulatory systems

What the researchers found

The mother and fetus independently produce and metabolize natriuretic peptides (ANP and BNP) — their circulations do not share these peptide hormones. In 244 fetal samples (86 with congenital heart defects, 31 with arrhythmia, 127 controls), there was no correlation between maternal and fetal levels of either ANP or BNP.

A key difference emerged between the two peptides: fetal ANP exists exclusively in its mature form and is rapidly metabolized by the placenta and umbilical vessels (umbilical vein levels were roughly double arterial levels). Fetal BNP, however, circulates predominantly as precursor forms (proBNP, glycosylated variants), which may protect it from placental degradation — BNP levels were similar between umbilical vein and artery. This has important implications for using natriuretic peptides as biomarkers for fetal heart disease.

Why it matters

Natriuretic peptides are the gold standard biomarkers for heart failure in adults, but their behavior in the fetal-placental circulation was poorly understood. This study shows that the placenta creates a complete barrier between maternal and fetal natriuretic peptide systems and actively metabolizes fetal ANP. This matters for prenatal diagnosis: measuring BNP (which survives placental metabolism) may be more reliable than ANP for assessing fetal cardiac stress from congenital heart defects.

The numbers in context

n=244 (86 congenital heart defect, 31 arrhythmia, 127 controls) · ANP regression coefficient UV:UA ≈ 0.5 · BNP regression coefficient UV:UA ≈ 1.0 · no maternal-fetal correlation · ANP = mature form only · BNP = predominantly precursor forms

How the study worked

Prospective cross-sectional study measuring plasma ANP and BNP concentrations in maternal vein, umbilical artery (UA), and umbilical vein (UV) samples. Three fetal groups were compared: congenital heart defects, arrhythmias, and normal controls. Molecular forms of immunoreactive ANP and BNP in UA plasma were characterized by chromatographic analysis.

Who was studied

244 fetuses: 86 with congenital heart defects, 31 with arrhythmia, and 127 normal controls, with paired maternal and umbilical cord blood samples

What this study cannot tell us

Cross-sectional design captures a single time point and cannot track changes over gestational age. The study focused on metabolic patterns rather than diagnostic accuracy for specific congenital heart defects. Molecular form analysis was performed on UA plasma only. The mechanism of placental ANP degradation is inferred from concentration gradients rather than directly measured. Sample sizes within specific congenital heart defect subtypes may be small.

How to read the evidence

This is a well-designed prospective clinical study with 244 fetal samples including appropriate disease and control groups, published in a peer-reviewed placenta biology journal. The 'Moderate' grade reflects the solid clinical data with molecular characterization, appropriate for an observational study.

When this study was published

Published in 2019, this study provides current understanding of natriuretic peptide metabolism in the fetal-placental unit. The findings remain relevant for prenatal biomarker development.

The bigger picture

Prenatal diagnosis of congenital heart disease is challenging, and non-invasive biomarkers could supplement ultrasound screening. Understanding how natriuretic peptides behave in the fetal-placental circulation is essential for developing cord blood or maternal blood tests for fetal cardiac stress. This study establishes that BNP/proBNP, not ANP, is the more stable biomarker candidate for fetal heart assessment.

Questions still open

Can cord blood BNP/proBNP levels reliably predict which congenital heart defects require immediate intervention after birth?
What specific placental enzymes are responsible for the rapid metabolism of fetal ANP?
Could measuring fetal BNP via cordocentesis improve prenatal management of complex congenital heart disease?

Common questions

What are natriuretic peptides and why do they matter for the fetal heart?

ANP and BNP are hormones released when the heart is under stress — stretched or overworked. In adults, elevated BNP is the standard blood test for heart failure. In fetuses with congenital heart defects, the heart is often stressed from structural problems. Measuring these peptides in cord blood could help doctors assess how much the fetal heart is struggling and plan treatment for after birth.

Why does the placenta destroy ANP but not BNP?

The study found that fetal ANP exists only in its mature, active form, which the placenta's enzymes can easily break down. Fetal BNP, however, circulates mostly as larger precursor forms (proBNP) that are protected from enzymatic degradation. This difference in molecular form determines whether the peptide survives placental transit, making BNP the more useful biomarker for assessing fetal cardiac health.

Read the original research

Metabolism of atrial and brain natriuretic peptides in the fetoplacental circulation of fetuses with congenital heart diseases.

Placenta, 83, 26-32

View on PubMed ↗Publisher’s paper ↗

Citation

Miyoshi, Takekazu; Hosoda, Hiroshi; Miyazato, Mikiya; Kangawa, Kenji; Yoshimatsu, Jun; Minamino, Naoto. (2019). Metabolism of atrial and brain natriuretic peptides in the fetoplacental circulation of fetuses with congenital heart diseases.. Placenta, 83, 26-32. https://doi.org/10.1016/j.placenta.2019.06.382