Opportunities for, and barriers to, uterus-preserving surgical techniques for placenta accreta spectrum.

INTRODUCTION: Placenta accreta spectrum (PAS) can lead to major peripartum morbidity. Appropriate management approaches depend on the clinical severity, each individual's preference, and the treating team's expertise. Peripartum hysterectomy is the most frequently used treatment option. However, it can impact psychological well-being and fertility. We investigated whether conservative treatment with focal resection or leaving the placenta in situ is associated with comparable or lower maternal morbidity than hysterectomy in centers of excellence within the International Society for placenta accreta spectrum (IS-PAS). Furthermore, a survey was conducted to explore potential barriers to conservative management in antenatal counseling and intraoperative decision-making. MATERIAL AND METHODS: Confirmed PAS cases in the prospective IS-PAS database from 22 registered centers between January 2020 and June 2022 were included in the analysis. A separate online survey with 21 questions was answered by the IS-PAS center experts about indications, diagnostic criteria, patient counseling, surgical practice, changes from the preoperative treatment plan, and why conservative management may not be offered. RESULTS: A total of 234 cases were included in the analysis: 186 women received hysterectomy and 38 women were treated by focal resection, and 10 by leaving the placenta in situ. Blood loss was lower in the focal resection group and in the placenta in situ group compared to the hysterectomy group (p = 0.04). 46.4% of the women initially planned for focal resection, and 35.7% of those initially planned for leaving the placenta in situ were ultimately treated by hysterectomy. Our survey showed that the IS-PAS centers preferred hysterectomy according to a woman's wishes (64%) and when they expected less blood loss and morbidity (41%). Eighteen percent of centers did not offer focal resection at all due to a lack of experience with this technique. Reasons for not offering to leave the placenta in situ were avoidance of unexpected reoperation (36%), puerperal infection (32%), or skepticism about the method (23%). CONCLUSIONS: Uterus-preserving treatment strategies such as focal resection appear to be safe alternatives to peripartum hysterectomy. However, less than half of the IS-PAS centers perform them. Acceptance of conservative treatments could be increased by standardized criteria for their implementation and by systematic training for PAS experts.

Involvement of the JAK-STAT pathway in the molecular landscape of tyrosine kinase fusion-negative hypereosinophilic syndromes: A nationwide CEREO study.

We investigated using a custom NGS panel of 149 genes the mutational landscape of 64 consecutive adult patients with tyrosine kinase fusion-negative hypereosinophilia (HE)/hypereosinophilic syndrome (HES) harboring features suggestive of myeloid neoplasm. At least one mutation was reported in 50/64 (78%) patients (compared to 8/44 (18%) patients with idiopathic HE/HES/HEUS used as controls; p < .001). Thirty-five patients (54%) had at least one mutation involving the JAK-STAT pathway, including STAT5B (n = 18, among which the hotspot N642H, n = 13), JAK1 (indels in exon 13, n = 5; V658F/L, n = 2), and JAK2 (V617F, n = 6; indels in exon 13, n = 2). Other previously undescribed somatic mutations were also found in JAK2, JAK1, STAT5B, and STAT5A, including three patients who shared the same STAT5A V707fs mutation and features consistent with primary polycythemia. Nearly all JAK-STAT mutations were preceded by (or associated with) myelodysplasia-related gene mutations, especially in RNA-splicing genes or chromatin modifiers. In multivariate analysis, neurologic involvement (hazard ratio [HR] 4.95 [1.87-13.13]; p = .001), anemia (HR 5.50 [2.24-13.49]; p < .001), and the presence of a high-risk mutation (as per the molecular international prognosis scoring system: HR 6.87 [2.39-19.72]; p < .001) were independently associated with impaired overall survival. While corticosteroids were ineffective in all treated JAK-STAT-mutated patients, ruxolitinib showed positive hematological responses including in STAT5A-mutated patients. These findings emphasize the usefulness of NGS for the workup of tyrosine kinase fusion-negative HE/HES patients and support the use of JAK inhibitors in this setting. Updated classifications could consider patients with JAK-STAT mutations and eosinophilia as a new "gene mutated-entity" that could be differentiated from CEL, NOS, and idiopathic HES.

Trends in antenatal corticosteroid administration: did our timing improve?

OBJECTIVES: We aimed to analyze trends in the rate of effective antenatal corticosteroid prophylaxis (ACS) administrations across a spectrum of typical diagnoses associated with preterm birth. METHODS: In this retrospective study we utilized delivery data after ACS from 2014 to 2020 at Charité Berlin, Germany. We evaluated the rate of effective ACS administrations defined as ≤10 days between last dose of ACS and delivery as well as the rate of post-ACS births on/after 37 + 0 weeks. We explored conditions associated with high rates of ineffective ACS administrations (>10 days before delivery). We analyzed the trend of ACS-effectiveness during the study period in the overall cohort and in placental dysfunction and cervical insufficiency diagnoses. RESULTS: The overall rate of effective ACS administrations was 42 % (709/1,672). The overall percentage of deliveries after/at 37 + 0 weeks following ACS administration was 19 % (343). Placenta previa, twin pregnancy and isthmocervical insufficiency were associated with ineffective ACS (19-34 % effective i.e. ≤10 days before delivery). The overall ratio of effective ACS applications rose over time (p=0.002). Over the course of this study ACS effectiveness increased in placental dysfunction and isthmocervical insufficiency diagnoses (p=0.028; p=0.001). CONCLUSIONS: Compared to a previous publication we found a decrease of post-ACS deliveries after/at 37 + 0 weeks (19 vs. 27 %). Ineffective ACS administrations are still frequent in patients with placenta previa, twin pregnancy and isthmocervical insufficiency. It remains to be investigated in future trials if the introduction of new diagnostic tools such as soluble Fms-like tyrosinkinase-1/placental growth factor (sFlt-1/PlGF) testing and placental alpha-microglobulin-1 (PAMG-1) testing directly led to an increased ACS effectiveness.

Sex differences in DNA methylation across gestation: a large scale, cross-cohort, multi-tissue analysis.

Biological sex is a key variable influencing many physiological systems. Disease prevalence as well as treatment success can be modified by sex. Differences emerge already early in life and include pregnancy complications and adverse birth outcomes. The placenta is a critical organ for fetal development and shows sex-based differences in the expression of hormones and cytokines. Epigenetic regulation, such as DNA methylation (DNAm), may underlie the previously reported placental sexual dimorphism. We associated placental DNAm with fetal sex in three cohorts. Individual cohort results were meta-analyzed with random-effects modelling. CpG-sites differentially methylated with sex were further investigated regarding pathway enrichment, overlap with methylation quantitative trait loci (meQTLs), and hits from phenome-wide association studies (PheWAS). We evaluated the consistency of findings across tissues (CVS, i.e. chorionic villus sampling from early placenta, and cord blood) as well as with gene expression. We identified 10,320 epigenome-wide significant sex-differentially methylated probes (DMPs) spread throughout the epigenome of the placenta at birth. Most DMPs presented with lower DNAm levels in females. DMPs mapped to genes upregulated in brain, were enriched for neurodevelopmental pathways and significantly overlapped with meQTLs and PheWAS hits. Effect sizes were moderately correlated between CVS and placenta at birth, but only weakly correlated between birth placenta and cord blood. Sex differential gene expression in birth placenta was less pronounced and implicated genetic regions only marginally overlapped with those associated with differential DNAm. Our study provides an integrative perspective on sex-differential DNAm in perinatal tissues underscoring the possible link between placenta and brain.

Uterine packing with chitosan-covered tamponade to treat postpartum hemorrhage.

Postpartum hemorrhage remains a major cause of maternal mortality and morbidity worldwide with higher rates found in resource-challenged countries. Conventional use of uterotonics such as oxytocin, prostaglandins, and medications to support coagulation, such as fibrinogen and tranexamic acid, are helpful but may not be sufficient to arrest life-threatening postpartum hemorrhage. Severe postpartum hemorrhage leads to an increased need for blood transfusions and the use of invasive techniques, such as intrauterine balloon tamponade, compression sutures, and arterial ligation, as advanced steps in the management cascade. In extreme cases where hemorrhage is resistant to these therapies, a hysterectomy may be necessary to avoid possible maternal death. Uterine packing with a chitosan-covered tamponade is an emerging tool in the armamentarium of the obstetrical team, especially when resources for advance surgical and other invasive options may be limited. Modified chitosan-impregnated gauze was originally described in the management of acute hemorrhage in the field of military medicine, combining the physiological antihemorrhaging effect of modified chitosan with a compression tamponade for the acute treatment of wound bleeding. The first described use in obstetrics was in 2012, showing that the chitosan-covered tamponade is an effective intervention to arrest ongoing therapy-resistant postpartum hemorrhage. Further studies showed a reduction in hysterectomies and blood transfusions. The method is, however, underreported and is not yet an established method used worldwide. To demonstrate the step-by-step application of the intrauterine chitosan-covered tamponade in the management of therapy-resistant postpartum hemorrhage, we have produced a teaching video to illustrate the important steps and techniques to optimize the effectiveness and safety of this novel intervention.

Apoptosis Inhibitor 5: A Multifaceted Regulator of Cell Fate.

Apoptosis, or programmed cell death, is a fundamental process that maintains tissue homeostasis, eliminates damaged or infected cells, and plays a crucial role in various biological phenomena. The deregulation of apoptosis is involved in many human diseases, including cancer. One of the emerging players in the intricate regulatory network of apoptosis is apoptosis inhibitor 5 (API5), also called AAC-11 (anti-apoptosis clone 11) or FIF (fibroblast growth factor-2 interacting factor). While it may not have yet the same level of notoriety as some other cancer-associated proteins, API5 has garnered increasing attention in the cancer field in recent years, as elevated API5 levels are often associated with aggressive tumor behavior, resistance to therapy, and poor patient prognosis. This review aims to shed light on the multifaceted functions and regulatory mechanisms of API5 in cell fate decisions as well as its interest as therapeutic target in cancer.

Venetoclax Combined with Intensive Chemotherapy: A New Hope for Refractory and/or Relapsed Acute Myeloid Leukemia?

Background. Primary resistance of acute myeloid leukemia (AML) to the conventional 3 + 7 intensive chemotherapy and relapses after first-line chemotherapy are two highly challenging clinical scenarios. In these cases, when allogeneic stem cell transplantation is feasible, patients are usually retreated with other chemotherapeutic regimens, as transplantation is still considered, nowadays, the only curative option. Methods. We discuss the mechanisms behind resistance to chemotherapy and offer a comprehensive review on current treatments of refractory/relapsed AML with a focus on novel approaches incorporating the BCL-2 inhibitor venetoclax. Results. Alas, complete remission rates after salvage chemotherapy remain relatively low, between 30 and 60% at best. More recently, the BCL-2 inhibitor venetoclax was combined either with hypomethylating agents or chemotherapy in refractory/relapsed patients. In particular, its combination with chemotherapy offered promising results by achieving higher rates of remission and bridging a substantial number of patients to transplantation. Conclusions. Venetoclax-based approaches might become, in the near future, the new standard of care for refractory/relapsed AML.

A Sustainable Translational Sheep Model for Planned Cesarean Delivery of Contraction-Free Ewes.

We evaluated whether the sheep constitutes a useful translational model to evaluate anatomical and surgical aspects of cesarean delivery (CD) from a human medical perspective with the aim of both maternal and neonatal well-being. Our hypothesis was that CD in contraction-free ewes is not associated with major complications. Primary endpoint was the transferability of anatomical conditions and surgical techniques of CD from the ewe to the human. Secondary endpoints were maternal and fetal survival, occurrence of retained fetal membranes, metritis, mastitis, or wound infections. Forty-eight Merino ewes were delivered by CD after 95% gestation (142-144 days). Both ewes and newborn lambs were cared for intensively after the delivery. Ovine uterine anatomy during CD appeared slightly different but comparable to the human uterus. Uterine incisions were mostly performed in the uterine horns, not in the uterine corpus. The ovine uterine wall is thinner than in humans. All ewes survived without any major complications. Seventy-seven (88.5%) out of 87 live-born lambs survived without any complications. The contraction-free ewe constitutes an appropriate and safe model to evaluate anatomical and surgical aspects of CD from a human medical perspective. We present a step-by-step manual for successfully planned cesarean delivery for sheep including the perioperative management illustrated with photographs and a five-minute video. With adequate planning and a reasonable number of staff, it is possible to safeguard both maternal and neonatal survival. This sustainable translational medicine model offers additional potential for the offspring to be used for further research studies (e.g., transgenerational inheritance research).

Analysis of maternal mortality in Berlin, Germany - discrepancy between reported maternal mortality and comprehensive death certificate exploration.

OBJECTIVES: The Organisation for Economic Cooperation and Development (OECD) estimates an average maternal mortality rate (MMR) of around 3.4 maternal deaths per 100,000 live births for 2019-2021, based on relevant diagnoses on death certificates. However, Germany does not currently have a registry for recording the number of maternal deaths. The aim of this study is to identify the actual number of maternal deaths in Berlin between 2019 and 2022, as well as sources of underreporting and causes of death. METHODS: Potential maternal mortality cases were identified through a search at the Berlin Central Archive for Death Certificates, inquiring women aged 15-50 years with indications of present or recent pregnancy on the death certificate. To cross match the database, an additional search at the Charité University Hospital Berlin was carried out, checking each individual file for pregnancy-association. RESULTS: The data search resulted in 2,316 women, 18 of which presented an association to pregnancy. Of these, 12 could be classified as maternal mortality cases (MMR 7.8/100,000). The additional search in a university setting revealed two further maternal mortality cases without prior indication of pregnancy on the death certificate. This results in a total MMR of 9.1/100,000 live births, which is over double the official estimate by the OECD. CONCLUSIONS: Based on our findings in Berlin, it can be estimated that there is significant underreporting regarding maternal death cases in Germany. A more comprehensive recording system is needed to more accurately portray maternal mortality.

Uterine scars after caesarean delivery: From histology to the molecular and ultrastructural level.

Uterine rupture during a trial of labor after caesarean delivery (CD) is a serious complication for mother and fetus. The lack of knowledge on histological features and molecular pathways of uterine wound healing has hindered research in this area from evolving over time. We analysed collagen content and turnover in uterine scars on a histological, molecular and ultrastructural level. Therefore, tissue samples from the lower uterine segment were obtained during CD from 16 pregnant women with at least one previous CD, from 16 pregnant women without previous CD, and from 16 non-pregnant premenopausal women after hysterectomy for a benign disease. Histomorphometrical collagen quantification showed, that the collagen content of the scar area in uterine wall specimens after previous CD was significantly higher than in the unscarred myometrium of the same women and the control groups. Quantitative real-time PCR of uterine scar tissue from FFPE samples delineated by laser microdissection yielded a significantly higher COL3A1 expression and a significantly lower COL1A2/COL3A1 ratio in scarred uteri than in samples from unscarred uteri. Histological collagen content and the expression of COL1A2 and COL3A1 were positively correlated, while COL1A2/COL3A1 ratio was negatively correlated with the histological collagen content. Transmission electron microscopy revealed a destroyed myometrial ultrastructure in uterine scars with increased collagen density. We conclude that the high collagen content in uterine scars results from an ongoing overexpression of collagen I and III. This is a proof of concept to enable further analyses of specific factors that mediate uterine wound healing.

Parity modulates impact of BMI and gestational weight gain on gut microbiota in human pregnancy.

Dysregulation of maternal adaptations to pregnancy due to high pre-pregnancy BMI (pBMI) or excess gestational weight gain (GWG) is associated with worsened health outcomes for mothers and children. Whether the gut microbiome contributes to these adaptations is unclear. We longitudinally investigated the impact of pBMI and GWG on the pregnant gut microbiome. We show that the gut microbiota of participants with higher pBMI changed less over the course of pregnancy in primiparous but not multiparous participants. This suggests that previous pregnancies may have persistent impacts on maternal adaptations to pregnancy. This ecological memory appears to be passed on to the next generation, as parity modulated the impact of maternal GWG on the infant gut microbiome. This work supports a role of the gut microbiome in maternal adaptations to pregnancy and highlights the need for longitudinal sampling and accounting for parity as key considerations for studies of the microbiome in pregnancy and infants. Understanding how these factors contribute to and shape maternal health is essential for the development of interventions impacting the microbiome, including pre/probiotics.

Alterations of materno-placento-fetal glucose homeostasis after a single course of antenatal betamethasone.

INTRODUCTION: Intrauterine growth impairment is associated with long-term metabolic changes (perinatal programming). We recently demonstrated that antenatal betamethasone (BET) decreased head circumference in term born females. Since glucose is the main energy source for fetal growth, BET-induced changes in maternal glucose homeostasis, a reduced transplacental glucose transfer or an altered fetal glucose utilization may be linked with the observed growth impairment. METHODS: 86 pregnant women exposed to BET (single course, <34 + 0 weeks of gestation (wks)) were compared to 92 gestational-age/sex-matched controls. Glucose, insulin, leptin, insulin-like growth factors (IGF-1, IGF-2) and their binding proteins (IGFBP-1, IGFBP-3) were measured in maternal and umbilical cord blood samples. Homeostasis Model Assessment (HOMA-IR) was calculated. Placental glucose transporter 1 and 3 (GLUT1, GLUT3) protein levels were determined. Statistics were performed for overall and subgroup analysis (gestational age, sex). RESULTS: After BET maternal HOMA-IR was elevated, IGFBP-1 reduced. In female pregnancies, glucose levels ≥37 + 0 wks and IGF-1 levels <37 + 0 wks were tendentially increased. Placental GLUT1 and GLUT3 protein levels were not significantly altered. Fetal umbilical venous glucose levels ≥37 + 0 wks were increased. HOMA-IR tended to be elevated in females. DISCUSSION: Growth impairment after BET appears neither caused by maternal nor fetal hypoglycemia nor changes of GLUT1 and GLUT3 total protein levels. Nonetheless, glucose homeostasis of mothers and daughters was altered even beyond the BET time frame (hyperglycemia, enhanced insulin resistance). Despite glucose supply was sufficient, an anabolic effect was apparently absent. Overall, our results highlight the relevance of adequate glucose management after BET and peripartum.

Use of tamibarotene, a potent and selective RARα agonist, in combination with azacitidine in patients with relapsed and refractory AML with RARA gene overexpression.

Tamibarotene-based therapy is a novel targeted approach for the treatment of relapsed/refractory (R/R) acute myeloid leukemia (AML) with retinoic acid receptor alpha (RARA) gene overexpression. Approximately, 50% of higher-risk myelodysplastic syndrome (MDS) patients and approximately 30% of AML patients are positive for RARA overexpression using a blood-based biomarker test that measures RARA expression in peripheral blasts. A phase 2 study investigating the activity of tamibarotene in patients with RARA overexpression was conducted in patients with AML and MDS (NCT02807558). In 28 patients with R/R AML and RARA overexpression treated with tamibarotene in combination with azacitidine, the median overall survival was 5.9 months. In 21 response-evaluable patients, the complete remission/complete remission with incomplete hematologic recovery (CR/CRi) rate was 19%, and median time to initial CR/CRi was 1.2 months. The favorable safety profile and preliminary clinical activity support the development of combination therapies with tamibarotene in myeloid malignancies with RARA overexpression.

TP53 Alterations in Myelodysplastic Syndromes and Acute Myeloid Leukemia.

TP53 mutations are less frequent in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) than in solid tumors, except in secondary and therapy-related MDS/AMLs, and in cases with complex monosomal karyotype. As in solid tumors, missense mutations predominate, with the same hotspot mutated codons (particularly codons 175, 248, 273). As TP53-mutated MDS/AMLs are generally associated with complex chromosomal abnormalities, it is not always clear when TP53 mutations occur in the pathophysiological process. It is also uncertain in these MDS/AML cases, which often have inactivation of both TP53 alleles, if the missense mutation is only deleterious through the absence of a functional p53 protein, or through a potential dominant-negative effect, or finally a gain-of-function effect of mutant p53, as demonstrated in some solid tumors. Understanding when TP53 mutations occur in the disease course and how they are deleterious would help to design new treatments for those patients who generally show poor response to all therapeutic approaches.

Olutasidenib (FT-2102) induces durable complete remissions in patients with relapsed or refractory IDH1-mutated AML.

Olutasidenib (FT-2102) is a potent, selective, oral, small-molecule inhibitor of mutant isocitrate dehydrogenase 1 (mIDH1). Overall, 153 IDH1 inhibitor-naive patients with mIDH1R132 relapsed/refractory (R/R) acute myeloid leukemia (AML) received olutasidenib monotherapy 150 mg twice daily in the pivotal cohort of this study. The median age of participants was 71 years (range, 32-87 years) and the median number of prior regimens received by patients was 2 (1-7). The rate of complete remission (CR) plus CR with partial hematologic recovery (CRh) was 35%, and the overall response rate was 48%. Response rates were similar in patients who had, and who had not, received prior venetoclax. With 55% of patients censored at the time of data cut-off, the median duration of CR/CRh was 25.9 months. The median duration of overall response was 11.7 months, and the median overall survival was 11.6 months. Of 86 patients who were transfusion dependent at baseline, a 56-day transfusion independence was achieved in 29 (34%), which included patients in all response groups. Grade 3 or 4 treatment-emergent adverse events (≥10%) were febrile neutropenia and anemia (n = 31; 20% each), thrombocytopenia (n = 25; 16%), and neutropenia (n = 20; 13%). Differentiation syndrome adverse events of special interest occurred in 22 (14%) patients, with 14 (9%) grade ≥3 and 1 fatal case reported. Overall, olutasidenib induced durable remissions and transfusion independence with a well-characterized and manageable side effect profile. The observed efficacy represents a therapeutic advance in this molecularly defined, poor-prognostic population of patients with mIDH1 R/R AML. This trial was registered at www.clinicaltrials.gov as #NCT02719574.

Aortitis PET Imaging in VEXAS Syndrome: A Case Report.

ABSTRACT: VEXAS (vacuoles, E1 enzyme, X-LINKED, autoinflammatory, somatic) syndrome is a complex inflammatory disease associated with somatic mutations of the ubiquitin-like modifier activating enzyme 1 (UBA1) gene. A 75-year-old man with a medical history of thrombophlebitis, leukocytoclastic vasculitis, chronic inflammatory arthralgia, elevated inflammatory markers, and anemia was diagnosed with VEXAS syndrome. 18F-FDG PET/CT showed thoracic aortitis, a rare involvement during VEXAS syndrome. Corticosteroid therapy monitored with 18F-FDG PET/CT led to a complete metabolic response.

European guidelines on perinatal care: corticosteroids for women at risk of preterm birth.

of recommendationsCorticosteroids should be administered to women at a gestational age between 24+0 and 33+6 weeks, when preterm birth is anticipated in the next seven days, as these have been consistently shown to reduce neonatal mortality and morbidity. (Strong-quality evidence; strong recommendation). In selected cases, extension of this period up to 34+6 weeks may be considered (Expert opinion). Optimal benefits are found in infants delivered within 7 days of corticosteroid administration. Even a single-dose administration should be given to women with imminent preterm birth, as this is likely to improve neurodevelopmental outcome (Moderate-quality evidence; conditional recommendation).Either betamethasone (12 mg administered intramuscularly twice, 24-hours apart) or dexamethasone (6 mg administered intramuscularly in four doses, 12-hours apart, or 12 mg administered intramuscularly twice, 24-hours apart), may be used (Moderate-quality evidence; Strong recommendation). Administration of two "all" doses is named a "course of corticosteroids".Administration between 22+0 and 23+6 weeks should be considered when preterm birth is anticipated in the next seven days and active newborn life-support is indicated, taking into account parental wishes. Clear survival benefit has been observed in these cases, but the impact on short-term neurological and respiratory function, as well as long-term neurodevelopmental outcome is still unclear (Low/moderate-quality evidence; Weak recommendation).Administration between 34 + 0 and 34 + 6 weeks should only be offered to a few selected cases (Expert opinion). Administration between 35+0 and 36+6 weeks should be restricted to prospective randomized trials. Current evidence suggests that although corticosteroids reduce the incidence of transient tachypnea of the newborn, they do not affect the incidence of respiratory distress syndrome, and they increase neonatal hypoglycemia. Long-term safety data are lacking (Moderate quality evidence; Conditional recommendation).Administration in pregnancies beyond 37+0 weeks is not indicated, even for scheduled cesarean delivery, as current evidence does not suggest benefit and the long-term effects remain unknown (Low-quality evidence; Conditional recommendation).Administration should be given in twin pregnancies, with the same indication and doses as for singletons. However, existing evidence suggests that it should be reserved for pregnancies at high-risk of delivering within a 7-day interval (Low-quality evidence; Conditional recommendation). Maternal diabetes mellitus is not a contraindication to the use of antenatal corticosteroids (Moderate quality evidence; Strong recommendation).A single repeat course of corticosteroids can be considered in pregnancies at less than 34+0 weeks gestation, if the previous course was completed more than seven days earlier, and there is a renewed risk of imminent delivery (Low-quality evidence; Conditional recommendation).

Questioning the fetal microbiome illustrates pitfalls of low-biomass microbial studies.

Whether the human fetus and the prenatal intrauterine environment (amniotic fluid and placenta) are stably colonized by microbial communities in a healthy pregnancy remains a subject of debate. Here we evaluate recent studies that characterized microbial populations in human fetuses from the perspectives of reproductive biology, microbial ecology, bioinformatics, immunology, clinical microbiology and gnotobiology, and assess possible mechanisms by which the fetus might interact with microorganisms. Our analysis indicates that the detected microbial signals are likely the result of contamination during the clinical procedures to obtain fetal samples or during DNA extraction and DNA sequencing. Furthermore, the existence of live and replicating microbial populations in healthy fetal tissues is not compatible with fundamental concepts of immunology, clinical microbiology and the derivation of germ-free mammals. These conclusions are important to our understanding of human immune development and illustrate common pitfalls in the microbial analyses of many other low-biomass environments. The pursuit of a fetal microbiome serves as a cautionary example of the challenges of sequence-based microbiome studies when biomass is low or absent, and emphasizes the need for a trans-disciplinary approach that goes beyond contamination controls by also incorporating biological, ecological and mechanistic concepts.