Table 2.
Research studies related to the two hypotheses: “sterile womb” vs. “in-utero microbial colonization”
| Reference | Region | Samples | Study subjects (n) | Methods | Major result | Support for hypothesis |
|---|---|---|---|---|---|---|
| Sterpu, et al. (2021) | Sweden | Three layers of placental tissue; amniotic fluid; vernix caseosa; and saliva, vaginal, and rectal samples | 76 | PCR, DNA sequencing techniques | No evidence to support the existence of a placental microbiome | Sterile womb |
| Leiby, et al. (2018) | USA | Placental samples | 40 (20 term and 20 preterm) | 16 S rRNA, shotgun metagenomics | No evidence to support the existence of a placental microbiome | Sterile womb |
| Li, et al. (2020) | USA | Fetal intestine | - | 16 S rRNA | Did not detect any bacterial DNA | Sterile womb |
| Stout, et al. (2013) | USA | Different regions of the placenta | 159 (127 term and 68 preterm) | Histological staining | Evidence of intracellular bacteria in the basal plate of the placenta in 27% of cases | In-utero microbial colonization |
| Younge, et al. (2019) | USA |
Human: endometrial surface (uterus), placenta, and amniotic membrane; Mice: fetal intestine |
Human: 10 (5 term and 5 preterm) | 16 S rRNA gene sequencing, fluorescence in situ hybridization, and bacterial culturing | Bacterial 16 S rDNA signatures were identified in the placentas of women; Lactobacillus and other microbes were present in murine fetal tissues | In-utero microbial colonization |
| de Goffau, et al. (2019) | UK | Placental samples | 537 (318 cases of adverse pregnancy outcome, 219 controls ) | 16 S rRNA, shotgun metagenomics | The human placenta does not have a microbiome | Sterile womb |
| Sharlandjieva, et al. (2023) | Canada | Placental villi, maternal decidua, and fetal embryonic organ tissues | 25 | 16 S rRNA gene sequencing | Failed to identify placental microbiota | Sterile womb |
| Seferovic, et al. (2019) | USA | Placental tissue | 52 (26 term and 26 preterm) | In situ hybridization, traditional histological methods, clinical culture methodologies | Placental microbes were detected by in situ hybridization | In-utero microbial colonization |
| Aagaard, et al. (2014) | USA | Placental specimens | 320 | 16 S rDNA and whole-genome shotgun sequencing and analysis | Placenta harbored a unique low-abundance microbiome | In-utero microbial colonization |
| Theis, et al. (2020a) | USA | Rhesus macaques: fetal and placental samples, uterine wall | Rhesus macaques: 4 | Culturing, qPCR, and 16 S rRNA gene sequencing | No existence of a placental microbiota | Sterile womb |
| Theis, et al. (2020b) | USA | Mice: fetal and placental samples | Mice: 11 | Culturing, qPCR, and 16 S rRNA gene sequencing | No consistent evidence for placental and fetal microbiota in mice | Sterile womb |