Definition and research guide
This page combines a MeSH definition, publication statistics and selected research abstracts. It is a starting point for reading the literature, not a medical textbook or a systematic evidence review.
Content available: 4 complete abstracts (742 words), 10 references. Full article text is not stored or reproduced here; follow the PMID, DOI or PMC links to read the original sources and their access terms.
Definition
A clear, yellowish liquid that envelopes the fetus inside the sac of amnion. In the first trimester, it is likely a transudate of maternal or fetal plasma. In the second trimester, amniotic fluid derives primarily from fetal lung and kidney. Cells or substances in this fluid can be removed for prenatal diagnostic tests (amniocentesis).
Definition: NLM Medical Subject Headings (MeSH) scope note (Public domain (U.S. National Library of Medicine); attribution requested). View the MeSH record.
Also known as: Amniotic Fluids; Fluid, Amniotic; Fluids, Amniotic; Amniotic Fluid Index; Amniotic Fluid Indices; Fluid Index, Amniotic; Fluid Indices, Amniotic; Index, Amniotic Fluid.
Where it fits in the MeSH classification
- Broader topics
- Fluids and Secretions; Fetus
- See also
- Embolism, Amniotic Fluid; Fetoscopy; Polyhydramnios; Oligohydramnios
Related concepts
Research landscape
PubMed indexes 20,040 records tagged with the MeSH heading “Amniotic Fluid” (counts retrieved 2026-10-31). 1,319 of them (6.6%) were published from 2020 onward, and the busiest period so far is through 1999 with 13,864 records.
Reviews account for 1,227 records (6.1%) and meta-analyses for 53. Randomized controlled trials number 162 (0.8%) as a share of all records on the topic. Randomized trials make up only a small share of this literature, so much of what is known comes from laboratory, observational or descriptive work.
Show the data
| Period | Records |
|---|---|
| through 1999 | 13,864 |
| 2000-2009 | 2,302 |
| 2010-2019 | 2,555 |
| 2020 onward | 1,319 |
Publication-type chart data
| Type | Records | Share |
|---|---|---|
| Reviews | 1,227 | 6.1% |
| Meta-analyses | 53 | 0.3% |
| Randomized controlled trials | 162 | 0.8% |
Method: PubMed query "Amniotic Fluid"[MeSH Terms] with publication-type and date filters, retrieved 2026-10-31.
Reading the evidence in anatomy and physiology
Anatomy describes how body structures are built and physiology describes how they normally work, so most findings here are descriptive or mechanistic rather than evidence about treatment. Much of what is known comes from dissection, imaging, tissue studies and experiments in animals, and measurements in healthy volunteers can differ from those in people with disease or at different ages. Normal ranges vary between individuals and populations. Check whether a result was measured in people or in another species, the age and health of the participants, and the method used.
Evidence from open-access studies
These open-access studies come from PubMed’s best-match results for this heading (papers whose main topic it is), ranked here by citation count, with one recent addition. Each abstract is reproduced in full under its recorded open licence so that you can read the authors’ own words. They illustrate the literature; they are not a systematic summary of it. Citation counts measure attention, not reliability or clinical benefit.
| Study / authors | Year | Source label / design | Europe PMC citations | Licence / source |
|---|---|---|---|---|
| Amniotic fluid from healthy term pregnancies does not harbor a detectable microbial community | 2018 | Research article Design not recorded in structured metadata | 120 | cc by PMID 29751830 · DOI · PMC5946436 |
| Microbiome profile of the amniotic fluid as a predictive biomarker of perinatal outcome | 2017 | Research article Design not recorded in structured metadata | 75 | cc by PMID 28939908 · DOI · PMC5610236 |
| Small extracellular vesicles secreted from human amniotic fluid mesenchymal stromal cells possess cardioprotective and promigratory potential | 2020 | Research article Design not recorded in structured metadata | 73 | cc by PMID 32146560 · DOI · PMC7060967 |
| Metabolomics Highlights Reduced Glutamate and Acetylcarnitine in the Amniotic Fluid of Cytomegalovirus-Infected Pregnant Women | 2026 | Research article Design not recorded in structured metadata | 2 | cc by PMID 41841159 · DOI · PMC13054862 |
Amniotic fluid from healthy term pregnancies does not harbor a detectable microbial community [1]
Abstract reading summary — source excerpts
- Opening excerpt
- Recent studies have conflicting data regarding the presence of intra-amniotic microbiota.
- Closing excerpt
- Viral reads were sparse in the amniotic fluid, and we found no evidence of a core viral community across samples.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (115 words)
Recent studies have conflicting data regarding the presence of intra-amniotic microbiota. Viral communities are increasingly recognized as important although overlooked components of the human microbiota. It is unknown if the developing fetus is exposed to a community of viruses (virome). Given the debate over the existence of an intra-amniotic microbial community and the importance of understanding how the infant gut is populated, we characterized the virome and bacterial microbiota of amniotic fluid from 24 uncomplicated term pregnancies using next-generation sequencing methods. Contrary to expectations, the bacterial microbiota of amniotic fluid was indistinguishable from contamination controls. Viral reads were sparse in the amniotic fluid, and we found no evidence of a core viral community across samples.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 29751830 · DOI · PMC5946436
Microbiome profile of the amniotic fluid as a predictive biomarker of perinatal outcome [2]
Abstract reading summary — source excerpts
- Opening excerpt
- Chorioamnionitis (CAM), an inflammation of the foetal membranes due to infection, is associated with preterm birth and poor perinatal prognosis.
- Closing excerpt
- Our findings indicate the possibility of predicting CAM prior to delivery based on the AF microbiome profile.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (199 words)
Chorioamnionitis (CAM), an inflammation of the foetal membranes due to infection, is associated with preterm birth and poor perinatal prognosis. The present study aimed to determine whether CAM can be diagnosed prior to delivery based on the bacterial composition of the amniotic fluid (AF). AF samples from 79 patients were classified according to placental inflammation: Stage III (n = 32), CAM; Stage II (n = 27), chorionitis; Stage 0-I (n = 20), sub-chorionitis or no neutrophil infiltration; and normal AF in early pregnancy (n = 18). Absolute quantification and sequencing of 16S rDNA showed that in Stage III, the 16S rDNA copy number was significantly higher and the α-diversity index lower than those in the other groups. In principal coordinate analysis, Stage III formed a separate cluster from Stage 0-I, normal AF, and blank. Forty samples were classified as positive for microbiomic CAM (miCAM) defined by the presence of 11 bacterial species that were found to be significantly associated with CAM and some parameters of perinatal prognosis. The diagnostic accuracy for CAM according to miCAM was: sensitivity, approximately 94%, and specificity, 79-87%. Our findings indicate the possibility of predicting CAM prior to delivery based on the AF microbiome profile.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 28939908 · DOI · PMC5610236
Small extracellular vesicles secreted from human amniotic fluid mesenchymal stromal cells possess cardioprotective and promigratory potential [3]
Abstract reading summary — source excerpts
- Opening excerpt
- Mesenchymal stromal cells (MSCs) exhibit antiapoptotic and proangiogenic functions in models of myocardial infarction which may be mediated by secreted small extracellular vesicles (sEVs).
- Closing excerpt
- Together, these data indicate that SS-hAFSC sEVs have multifactorial beneficial effects in a myocardial infarction setting.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (210 words)
Mesenchymal stromal cells (MSCs) exhibit antiapoptotic and proangiogenic functions in models of myocardial infarction which may be mediated by secreted small extracellular vesicles (sEVs). However, MSCs have frequently been harvested from aged or diseased patients, while the isolated sEVs often contain high levels of impurities. Here, we studied the cardioprotective and proangiogenic activities of size-exclusion chromatography-purified sEVs secreted from human foetal amniotic fluid stem cells (SS-hAFSCs), possessing superior functional potential to that of adult MSCs. We demonstrated for the first time that highly pure (up to 1.7 × 1010 particles/µg protein) and thoroughly characterised SS-hAFSC sEVs protect rat hearts from ischaemia-reperfusion injury in vivo when administered intravenously prior to reperfusion (38 ± 9% infarct size reduction, p < 0.05). SS-hAFSC sEVs did not protect isolated primary cardiomyocytes in models of simulated ischaemia-reperfusion injury in vitro, indicative of indirect cardioprotective effects. SS-hAFSC sEVs were not proangiogenic in vitro, although they markedly stimulated endothelial cell migration. Additionally, sEVs were entirely responsible for the promigratory effects of the medium conditioned by SS-hAFSC. Mechanistically, sEV-induced chemotaxis involved phosphatidylinositol 3-kinase (PI3K) signalling, as its pharmacological inhibition in treated endothelial cells reduced migration by 54 ± 7% (p < 0.001). Together, these data indicate that SS-hAFSC sEVs have multifactorial beneficial effects in a myocardial infarction setting.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 32146560 · DOI · PMC7060967
Metabolomics Highlights Reduced Glutamate and Acetylcarnitine in the Amniotic Fluid of Cytomegalovirus-Infected Pregnant Women [4]
Abstract reading summary — source excerpts
- Opening excerpt
- Cytomegalovirus (CMV) is a major cause of morbidity in immunocompromised individuals and represents the leading infectious cause of neonatal congenital deafness.
- Closing excerpt
- These alterations may reflect early perturbations of neurobiochemical pathways with unknown effects on babies negative at birth, supporting the need for risk assessment and clinical monitoring even in the absence of congenital CMV infection.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (218 words)
Cytomegalovirus (CMV) is a major cause of morbidity in immunocompromised individuals and represents the leading infectious cause of neonatal congenital deafness. When acquired during pregnancy, CMV can be vertically transmitted to the fetus, potentially resulting in permanent sequelae characterized by intellectual and neurosensory impairments. To investigate metabolic alterations associated with primary maternal CMV infection, we conducted a metabolomics-based analysis of amniotic fluid (AF) from pregnant women who acquired CMV infection during the first trimester, as confirmed by IgG seroconversion, IgM positivity, and low-to-moderate IgG avidity indices. Our findings revealed that the AF metabolomic profiles from CMV transmitter and nontransmitter mothers were remarkably similar. In contrast, both the CMV-exposed groups showed profound metabolic dysregulation compared to uninfected controls, suggesting that CMV-related metabolic disparities may persist irrespective of vertical transmission. Specifically, we observed a significant downregulation of glutamate (p p < 0.0001) in CMV groups compared to control AF samples. Notably, the combined reduction of these two metabolites emerged as a surrogate biomarker signature of recent primary CMV infection of the mother, indicating that AF from both transmitting and nontransmitting pregnancies may share common metabolic adaptations. These alterations may reflect early perturbations of neurobiochemical pathways with unknown effects on babies negative at birth, supporting the need for risk assessment and clinical monitoring even in the absence of congenital CMV infection.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 41841159 · DOI · PMC13054862
Key reviews and meta-analyses
The most cited review-type papers among PubMed’s best-match results for this heading, listed with bibliographic details only. Follow the links for the full text and access terms.
- Research article Amniotic fluid: not just fetal urine anymore [5]
- Research article Diagnosis and surveillance of late-onset fetal growth restriction [6]
- Research article Meconium-stained amniotic fluid and the meconium aspiration syndrome. An update [7]
- Research article N-Acylethanolamines in human reproductive fluids [8]
- Research article Physiology of amniotic fluid volume regulation [9]
- Research article Role of the fetus in perinatal infection and neonatal brain damage [10]
References
- Lim ES, Rodriguez C, Holtz LR. Amniotic fluid from healthy term pregnancies does not harbor a detectable microbial community. . 2018. PMID 29751830 · DOI · PMC5946436
- Urushiyama D, Suda W, Ohnishi E, Araki R, Kiyoshima C, Kurakazu M, et al.. Microbiome profile of the amniotic fluid as a predictive biomarker of perinatal outcome. . 2017. PMID 28939908 · DOI · PMC5610236
- Takov K, He Z, Johnston HE, Timms JF, Guillot PV, Yellon DM, et al.. Small extracellular vesicles secreted from human amniotic fluid mesenchymal stromal cells possess cardioprotective and promigratory potential. . 2020. PMID 32146560 · DOI · PMC7060967
- Costanzo M, Miceli M, Campesi I, Bianco S, Mazzarelli LL, Migliorini S, et al.. Metabolomics Highlights Reduced Glutamate and Acetylcarnitine in the Amniotic Fluid of Cytomegalovirus-Infected Pregnant Women. . 2026. PMID 41841159 · DOI · PMC13054862
- Underwood MA, Gilbert WM, Sherman MP. Amniotic fluid: not just fetal urine anymore. J Perinatol. 2005. PMID 15861199 · DOI
- Figueras F, Caradeux J, Crispi F, Eixarch E, Peguero A, Gratacos E. Diagnosis and surveillance of late-onset fetal growth restriction. Am J Obstet Gynecol. 2018. PMID 29422212 · DOI
- Cleary GM, Wiswell TE. Meconium-stained amniotic fluid and the meconium aspiration syndrome. An update. Pediatr Clin North Am. 1998. PMID 9653434 · DOI
- Schuel H, Burkman LJ, Lippes J, Crickard K, Forester E, Piomelli D, et al.. N-Acylethanolamines in human reproductive fluids. Chem Phys Lipids. 2002. PMID 12505702 · DOI
- Brace RA. Physiology of amniotic fluid volume regulation. Clin Obstet Gynecol. 1997. PMID 9199840 · DOI
- Dammann O, Leviton A. Role of the fetus in perinatal infection and neonatal brain damage. Curr Opin Pediatr. 2000. PMID 10763757 · DOI
About this article
- Sources
- NLM Medical Subject Headings (definition, synonyms); NCBI PubMed (counts, identifiers); Europe PMC (open-access abstracts and citation counts).
- Verification
- Every reference was resolved against PubMed on 2026-10-31; title, year and DOI matched.
- Review state
- automated source verified; no human expert review has been recorded yet.
- Version
- 1, last updated 2026-10-31.
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Evidence strength
EvidenceHelix's computed view of the study designs behind this topic: how common meta-analyses, randomized trials and reviews are, how recent the literature is, and a plain-language reading. It describes the design mix of the literature. It is not a quality appraisal of any study, and it is not medical advice.