Surge of immune cell formation at birth differs by mode of delivery and infant characteristics-A population-based cohort study

Severe congenital T-lymphocytopenia may affect the outcome of neonatal intensive care

AIM

Circular DNA segments TREC (T-cell receptor excision circles) formed during T-lymphocyte maturation in the thymus, are a sensitive marker of thymic lymphocyte production in a broader manner. Quantification using qPCR is proposed as a surrogate marker of T cell malfunction in various primary and secondary conditions in a non-SCID selected risk newborn population.

METHODS

We collected 207 dry blood spot samples during the years 2015-2018, from newly admitted risk newborns. TREC values calculated per 106 cells were determined and a cut-off values of 5th percentile was set. The positive control group consisted of patients (n=13) with genetically confirmed SCID.

RESULTS

The median TREC value was 34,591.56 (18,074.08-60,228.58) for girls resp. 28,391.20 (13,835.01-51,835.93) per 106 cells for boys, P=0.046. Neonates born by C-section have been found to have higher TREC levels compared to neonates born by spontaneous delivery (P=0.018). In the group of preterm newborns (n=104), 3.8% had TREC value < 5th percentile, half of them died due to sepsis as opposed to no fatalities in preterm newborns with sepsis and TREC value > 5th percentile. In the group of term newborns (n=103) 9 children (8.7%) had TREC < 5th percentile, half of them were treated for asphyxia, with no fatal complications.

CONCLUSION

TREC levels calculated for the 5th percentile of a risk neonatal group is suggested as a surrogate marker for increased risk of fatal septic complication. Early recognition of these newborns within a risk scoring system using TREC levels could lead to potentially lifesaving interventions.

Effects on neonatal immunoglobulin concentrations by infant mode of delivery in the upstate KIDS study (2008-2010)

PROBLEM

Previous studies document an association between mode of delivery (MOD) and allergic conditions in children. Immunoglobulin (Ig) concentrations at birth may play a role. The goal of this study is to assess the impact of MOD on Ig concentrations at delivery from newborn dried blood spots (DBS).

METHOD OF STUDY

The Upstate KIDS Study (2008-2010) is a prospective cohort of mother-child pairs recruited from New York State, excluding New York City. Ig subtypes IgA, IgE, IgG1 , IgG2 , IgG3 , IgG4 , and IgM were measured in residual NDBS from the Newborn Screening Program (N = 3274 infants). MOD was categorized as vaginal delivery (VD), emergency cesarean delivery (ECD) or planned cesarean delivery (PCD). Associations between MOD and Ig levels were assessed using ANOVA and multiple regression, with models adjusted for gestational age, birth weight, maternal race, plurality, and smoking status.

RESULTS

IgA, and the IgG subtypes IgG3 and IgG4 were found to be significantly lower in PCD neonates relative to VD neonates in adjusted regression models: 3.57 mg/ml, (95% CI: 3.51, 3.63) compared to 3.64 mg/ml (95% CI: 3.59, 3.69); 8.95 ng/ml (95% CI: 8.88,9.03) compared to 9.03 ng/ml (95% CI: 8.98, 9.08) and 8.05 ng/ml (95% CI: 7.91, 8.20) compared to 8.22 ng/ml (95% CI: 7.91,8.20), respectively.

CONCLUSIONS

MOD may thus be related to neonatal immune profile. Results were found to be robust to sensitivity testing based on maternal complications and indication for CD. Clinical implications are unclear given the small levels of association found in newborns, but the result suggests greater susceptibility to infection, and further study is warranted.

Disquiet concerning cesarean birth

Cesarean birth has increased substantially in many parts of the world over recent decades and concerns have been raised about the propriety of this change in obstetric practice. Sometimes, a cesarean is necessary to preserve fetal and maternal health. But in balancing the risks of surgical intervention the implicit assumption has been that cesarean birth is an equivalent alternative to vaginal birth from the standpoint of the immediate and long-term health of the fetus and neonate. Increasingly, we realize this is not necessarily so. Delivery mode per se may influence short-term and abiding problems with homeostasis in offspring, quite independent of the indications for the delivery and other potentially confounding factors. The probability of developing various disorders, including respiratory compromise, obesity, immune dysfunction, and neurobehavioral disorders has been shown in some studies to be higher among individuals born by cesarean. Moreover, many of these adverse effects are not confined to the neonatal period and may develop over many years. Although the associations between delivery mode and long-term health are persuasive, their pathogenesis and causality remain uncertain. Full exploration and a clear understanding of these relationships is of great importance to the health of offspring.

Mode of Birth Is Not Associated With Food Allergy Risk in Infants

BACKGROUND

The association between mode of delivery and the risk of food allergy remains unclear due to the absence of studies with both challenge-proven food allergy outcomes and detailed information on the type of caesarean delivery.

OBJECTIVE

We assessed whether emergency or elective caesarean, or caesarean delivery in the presence or absence of labor initiation, is associated with the risk of food allergy.

METHODS

The HealthNuts study recruited 5276 12-month-old infants who underwent skin prick testing and oral food challenge to ascertain food allergy status, and linked the child's study data to additional birth data from the Victorian Perinatal Data Collection.

RESULTS

Parents of 3006 children consented to data linkage, and birth data were obtained on 2045. In this subgroup, 30% were born by caesarean and 13% had food allergy. Caesarean delivery, compared with vaginal birth, was not associated with the risk of food allergy (adjusted odds ratio [aOR]: 0.95, 95% confidence interval [CI]: 0.70, 1.30). Neither caesarean delivery before the onset of labor, nor after the onset of labor, was associated with the risk of food allergy (aOR: 0.83, 95% CI: 0.55-1.23 and aOR: 1.13, 95% CI: 0.75-1.72, respectively). Delivery by elective or emergency caesarean, compared with vaginal delivery, was not associated with risk of food allergy (aOR: 1.05, 95% CI: 0.71-1.55 and aOR: 0.86, 95% CI: 0.56-1.31). There was no evidence of effect modification by breastfeeding, older siblings, pet dog ownership, or maternal allergy.

CONCLUSION

Caesarean delivery, either with or without labor, or elective or emergency, was not associated with the risk of food allergy in a population-based cohort of 12-month-old infants.

Microorganisms in the reproductive system and probiotic's regulatory effects on reproductive health

The presence of microbial communities in the reproductive tract has been revealed, and this resident microbiota is involved in the maintenance of health. Intentional modulation via probiotics has been proposed as a possible strategy to enhance reproductive health and reduce the risk of diseases. The male seminal microbiota has been suggested as an important factor that influences a couple’s health, pregnancy outcomes, and offspring health. Probiotics have been reported to play a role in male fertility and to affect the health of mothers and offspring. While the female reproductive microbiota is more complicated and has been identified in both the upper and lower reproductive systems, they together contribute to health maintenance. Probiotics have shown regulatory effects on the female reproductive tract, thereby contributing to homeostasis of the tract and influencing the health of offspring. Further, through transmission of bacteria or through other indirect mechanisms, the parent’s reproductive microbiota and probiotic intervention influence infant gut colonization and immunity development, with potential health consequences. In vitro and in vivo studies have explored the mechanisms underlying the benefits of probiotic administration and intervention, and an array of positive results, such as modulation of microbiota composition, regulation of metabolism, promotion of the epithelial barrier, and improvement of immune function, have been observed. Herein, we review the state of the art in reproductive system microbiota and its role in health and reproduction, as well as the beneficial effects of probiotics on reproductive health and their contributions to the prevention of associated diseases.

Altered stress responses in adults born by Caesarean section

Birth by Caesarean-section (C-section), which increases the risk for metabolic and immune disorders, disrupts the normal initial microbial colonisation of the gut, in addition to preventing early priming of the stress and immune-systems.. Animal studies have shown there are enduring psychological processes in C-section born mice. However, the long-term impact of microbiota-gut-brain axis disruptions due to birth by C-section on psychological processes in humans is unknown. Forty age matched healthy young male university students born vaginally and 36 C-section delivered male students were recruited. Participants underwent an acute stressor, the Trier social stress test (TSST), during a term-time study visit. A subset of participants also completed a study visit during the university exam period, representing a naturalistic stressor. Participants completed a battery of cognitive tests and self-report measures assessing mood, anxiety, and perceived stress. Saliva, blood, and stool samples were collected for analysis of cortisol, peripheral immune profile, and the gut microbiota. Young adults born by C-section exhibit increased psychological vulnerability to acute stress and a prolonged period of exam-related stress. They did not exhibit an altered salivary cortisol awakening response to the TSST, but their measures of positive affect were significantly lower than controls throughout the procedure. Both C-section and vaginally-delivered participants performed equally well on cognitive assessments. Most of the initial effects of delivery mode on the gut microbiome did not persist into adulthood as the gut microbiota profile showed modest changes in composition in adult vaginally-delivered and C-sectioned delivered subjects. From an immune perspective, concentrations of IL-1β and 1L-10 were higher in C-section participants. These data confirm that there is a potential enduring effect of delivery mode on the psychological responses to acute stress during early adulthood. The mental health implications of these observations require further study regarding policies on C-section use.

Immunological Findings and Clinical Outcomes of Infants With Positive Newborn Screening for Severe Combined Immunodeficiency From a Tertiary Care Center in the U.S

The implementation of severe combined immunodeficiency (SCID) newborn screening has played a pivotal role in identifying these patients early in life as well as detecting various milder forms of T cell lymphopenia (TCL). In this study we reviewed the diagnostic and clinical outcomes, and interesting immunology findings of term infants referred to a tertiary care center with abnormal newborn SCID screens over a 6-year period. Key findings included a 33% incidence of non-SCID TCL including infants with novel variants in FOXN1, TBX1, MYSM1, POLD1, and CD3E; 57% positivity rate of newborn SCID screening among infants with DiGeorge syndrome; and earlier diagnosis and improved transplant outcomes for SCID in infants diagnosed after compared to before implementation of routine screening. Our study is unique in terms of the extensive laboratory workup of abnormal SCID screens including lymphocyte subsets, measurement of thymic output (TREC and CD4TE), and lymphocyte proliferation to mitogens in nearly all infants. These data allowed us to observe a stronger positive correlation of the absolute CD3 count with CD4RTE than with TREC copies, and a weak positive correlation between CD4RTE and TREC copies. Finally, we did not observe a correlation between risk of TCL and history of prenatal or perinatal complications or low birth weight. Our study demonstrated SCID newborn screening improves disease outcomes, particularly in typical SCID, and allows early detection and discovery of novel variants of certain TCL-associated genetic conditions.

Association of Cesarean Delivery with Childhood Hospitalization for Infections Before 13 Years of Age

OBJECTIVES

To determine the association between cesarean delivery and childhood infections up to 13 years of age.

STUDY DESIGN

We conducted a longitudinal cohort study of 731 803 children born between 2006 and 2016 at all hospitals in the province of Quebec, Canada. We followed children born by cesarean, operative vaginal, and nonoperative vaginal delivery up to 13 years of age. Outcomes included hospitalization for otitis media, respiratory, infectious enteritis, and other infections. We estimated hazard ratios with 95% CIs for the association between mode of delivery and childhood infections, adjusted for patient characteristics.

RESULTS

At age 3-4 years, cesarean delivery was associated with a 1.07-fold greater risk of otitis media (95% CI, 1.03-1.11), a 1.15-fold greater risk of respiratory infection (95% CI, 1.09-1.22), and a 1.13-fold greater risk of infectious enteritis (95% CI, 1.03-1.25) compared with nonoperative vaginal delivery. However, operative vaginal delivery was associated with these same outcomes. Both cesarean and operative vaginal delivery were more strongly associated with infection hospitalization before age 1 year, but associations disappeared after 5 years.

CONCLUSIONS

Cesarean delivery is associated with infection hospitalization before but not after age 5 years. However, associations were also present for operative vaginal delivery, which suggests that mechanisms other than exposure to maternal vaginal flora explain the relationship.

Elective Caesarean Delivery Associated with Infant Hospitalisation for Intestinal But Not Respiratory Infection

OBJECTIVES

We assessed the impact of caesarean delivery on offspring respiratory and intestinal infection.

METHODS

Data were extracted from all live births (n = 429,058) occurring in the Australian state of Queensland between January 2009 and December 2015, and followed for 12 months. Births were categorised as either non-medically indicated caesarean or vaginal delivery and each offspring had a record (present/absent) of respiratory and intestinal infection hospitalisation for each month from birth to 12 months.

RESULTS

Infants delivered by non-medically indicated caesarean were more likely to experience respiratory infection [OR = 1.51 (1.15, 1.99)] and intestinal infection [OR = 1.74 (1.19, 2.55)] than those born by vaginal delivery. In the propensity score weighted analyses the estimate for respiratory infection was similar but non-significant [OR = 1.52 (0.99, 2.31)], while the association with intestinal infection strengthened [OR = 2.21 (1.25, 3.89)].

CONCLUSIONS FOR PRATICE

Our findings provide strong evidence for a specific and clinically meaningful link between non-medically indicated caesarean delivery and infant intestinal infection.

Delivery mode and future infectious morbidity of the offspring: a sibling analysis

PURPOSE

Cesarean delivery (CD) has been recently suggested to be associated with offspring's long-term health implications. We aimed to investigate the association between delivery mode and long-term infectious morbidity of the offspring while employing sibling matched analysis to maximize confounder control.

METHODS

A retrospective population-based cohort study was performed, which included all sibling deliveries occurring between 1991 and 2014 at a regional tertiary medical center. Offsprings were followed up until the age of 18 years. The study included 13,516 individuals (6758 sibling pairs): the first born was via vaginal delivery and the second via CD. Each siblings pair was considered a matched set, with the aim to perform a within-family analysis. A Kaplan-Meier survival curve was used to compare the cumulative infectious morbidity incidence and a multivariable Cox survival hazards regression model to control for confounders.

RESULTS

Crude rates of total infectious hospitalizations were found to be significantly higher in the CD group (OR 1.25; 95% CI 1.12-1.40). Specifically, bronchiolitis (OR 2.02, 95% CI 1.56-2.63), otitis (OR 1.52, 95% CI 1.21-1.9), and gastroenteritis (OR 1.41, 95% CI 1.05-1.9) were all found to be significantly more common in the CD group. The survival curve demonstrated significantly higher cumulative infection-related hospitalization rates in the CD group (log-rank p < 0.001). The Cox model, adjusted for several confounders, confirmed the significant association between CD and offspring's infection-related morbidity (adjusted HR 1.25; 95% CI 1.02-1.53).

CONCLUSION

CD appears to be independently associated with later offspring infection-related morbidity, even while rigorously adjusting for confounders.

Adverse pregnancy outcomes and risk of later allergic rhinitis-Nationwide Swedish cohort study

BACKGROUND

Perinatal conditions may be associated with future allergic disease; however, data are conflicting and incomplete for childhood allergic rhinitis (AR). The aim of this study was to examine pregnancy outcome (cesarean delivery, preterm birth, low birthweight) and offspring AR as defined by national registers.

METHODS

Nationwide longitudinal cohort study using prospectively recorded register data from 1 059 600 singleton livebirths born in Sweden in 2001-2012. Cox regression adjusted for infant sex and maternal factors (age at delivery, country of birth, parity, smoking, body mass index, and asthma/pulmonary disease) estimated hazard ratios (HRs) for AR during childhood.

RESULTS

During the study period 2001-2013, 22 386 (2.11%) children were diagnosed with AR. AR was more common in infants born through cesarean delivery (2.34%) than in those born vaginally (2.10%) (HR = 1.12; 95% confidence interval [95% CI] = 1.08-1.16). This was equivalent to one extra case of AR in 383 children followed up in our study. AR was also associated with moderately preterm birth (≥32-36 weeks of gestation: HR = 1.12, 95% CI = 1.04-1.20), large for gestational age (HR = 1.05, 95% CI = 1.01-1.10), and low (<7) 5-minute Apgar score (HR = 1.15, 95% CI = 1.02-1.30). Similar risk estimates were obtained when we restricted the outcome to ≥2 hospital-based records of AR. No association was observed between very preterm birth, post-term birth, low birthweight, or small for gestational age and AR.

CONCLUSION

Our study indicates an association between pregnancy outcomes and childhood AR, although observed effect sizes were generally modest.

T-cell Receptor Excision Circles in Newborns with Heart Defects

In the fetus, the cardiac neural crest gives rise to both the thymus and the conotruncus of the heart. In newborn screening for severe T-cell lymphopenia neonates with congenital heart defects may be detected. In this study, we investigated the occurrence of T-cell lymphopenia in neonates with or without 22q11.2 deletion syndrome (del) suffering from heart defects. This retrospective cohort study included 125 patients with heart defects. T-cell receptor excision circles (TRECs), a measure for T-cell lymphopenia, were quantified by RT-PCR using stored newborn screening blood spots. Three patient groups were compared: non-conotruncal defects (n = 57), conotruncal defects (n = 42), and 22q11.2 del with conotruncal defects (n = 26). Significantly lower TREC values were detected in patients with 22q11.2 del and conotruncal heart defects compared to those with non-syndromic conotruncal (p < 0.001) and non-conotruncal (p < 0.001) defects. In contrast, no significant difference was found between patients with non-syndromic conotruncal and non-conotruncal heart defects (p = 0.152). Low TREC levels were obtained in neonates treated with heart surgery/intervention within 2 weeks after birth and in those with a fatal outcome (p = 0.02) independent of patient group. A correlation was found between low TREC numbers and oxygen saturation, SpO₂ below 95% (p = 0.017). The SpO₂ was significantly lower in the non-syndromic conotruncal group compared to non-conotruncal (p < 0.001) and 22q11.2 del group (p = 0.015). No correlation was found between low neonatal TRECs and infections needing hospitalization later in life (p = 0.135). Patients with 22q11.2 del and conotruncal defects have significantly lower TREC levels compared to patients with heart defects without this syndrome.

Sexual Dimorphism in Immune Development and in Response to Nutritional Intervention in Neonatal Piglets

Although sex disparity in immunological function and susceptibility to various inflammatory and infectious disease is recognized in adults, far less is known about the situation in young infants during immune development. We have used an outbred piglet model to explore potential early sex disparity underlying both mucosal immune development and systemic responses to novel antigen. Despite similarities in intestinal barrier function and therefore, presumably, antigen exposure, females had less CD172⁺ (Sirp-α) antigen presenting cells and expression of MHCIIDR at 28 days old compared to males, along with greater regulatory T-cell numbers. This suggests that, during infancy, females may have greater potential for local immune regulation than their male counterparts. However, females also presented with significantly greater systemic antibody responses to injected ovalbumin and dietary soya. Females also synthesized significantly more IgA in mesenteric lymph nodes, whereas males synthesized more in caecal mucosa, suggesting that plasma cells were retained within the MLN in females, but increased numbers of plasma cells circulated through to the mucosal tissue in males. Significant effects of inulin and Bifidobacterium lactis NCC2818 on the developing immune system were also sex-dependent. Our results may start to explain inconsistencies in outcomes of trials of functional foods in infants, as distinction between males and females is seldom made. Since later functionality of the immune system is highly dependent on appropriate development during infancy, stratifying nutritional interventions by sex may present a novel means of optimizing treatments and preventative strategies to reduce the risk of the development of immunological disorders in later life.

Influence of maternal microbiota during pregnancy on infant immunity

Microbiota from various maternal sites, including the gut, vagina and breast milk, are known to influence colonization in infants. However, emerging evidence suggests that these sites may exert their influence prior to delivery, in turn influencing fetal immune development. The dogma of a sterile womb continues to be challenged. Regardless, there is convincing evidence that the composition of the maternal gut prior to delivery influences neonatal immunity. Therefore, while the presence and function of placental microbiome is not clear, there is consensus that the gut microbiota during pregnancy is a critical determinant of offspring health. Data supporting the notion of bacterial translocation from the maternal gut to extra-intestinal sites during pregnancy are emerging, and potentially explain the presence of bacteria in breast milk. Much evidence suggests that the maternal gut microbiota during pregnancy potentially determines the development of atopy and autoimmune phenotypes in offspring. Here, we highlight the role of the maternal microbiota prior to delivery on infant immunity and predisposition to diseases. Moreover, we discuss potential mechanisms that underlie this phenomenon.

Glycan Utilisation and Function in the Microbiome of Weaning Infants

Glycans are present exogenously in the diet, expressed and secreted endogenously by host cells, and produced by microbes. All of these processes result in them being available to the gut microbiome, firmly placing glycans at the interface of diet–microbe–host interactions. The most dramatic shift in dietary sources of glycans occurs during the transition from the milk-based neonatal diet to the diverse omnivorous adult diet, and this has profound effects on the composition of the gut microbiome, gene expression by microbes and host cells, mucin composition, and immune development from innate towards adaptive responses. Understanding the glycan-mediated interactions occurring during this transitional window may inform dietary recommendations to support gut and immune development during a vulnerable age. This review aims to summarise the current state of knowledge on dietary glycan mediated changes that may occur in the infant gut microbiome and immune system during weaning.

Infant Complementary Feeding of Prebiotics for theMicrobiome and Immunity

Complementary feeding transitions infants from a milk-based diet to solid foods, providing essential nutrients to the infant and the developing gut microbiome while influencing immune development. Some of the earliest microbial colonisers readily ferment select oligosaccharides, influencing the ongoing establishment of the microbiome. Non-digestible oligosaccharides in prebiotic-supplemented formula and human milk oligosaccharides promote commensal immune-modulating bacteria such as Bifidobacterium, which decrease in abundance during weaning. Incorporating complex, bifidogenic, non-digestible carbohydrates during the transition to solid foods may present an opportunity to feed commensal bacteria and promote balanced concentrations of beneficial short chain fatty acid concentrations and vitamins that support gut barrier maturation and immunity throughout the complementary feeding window.

Mode of delivery by an ulcerative colitis mother in a case of twins: Immunological differences in cord blood and placenta

AIM

To understand the effects of delivery mode on the immune cells frequency and function in cord blood and placenta.

METHODS

We evaluated immunological differences in cord blood and placental tissues for a case of twins one of which delivered vaginally while the other delivered by caesarian section (C-section). Cord blood mononuclear cells were isolated and placenta tissues were processed for cell isolation. Immune phenotyping was performed by flow cytometry methods following staining for T cells, natural killer (NK) cells, monocytes, neutrophils and CD71⁺ erythroid cells in both cord blood and placenta tissues. In addition, fetal calprotectin of twins was measured 12 wk after birth.

RESULTS

We found lower percentages of immune cells (e.g. T cells, monocytes and neutrophils) in the cord blood of C-section delivered compared to vaginally delivered newborn. In contrast, percentages of monocytes and neutrophils were > 2 folds higher in the placental tissues of C-section delivered newborn. More importantly, we observed lower percentages of CD71⁺ erythroid cells in both cord blood and placental tissues of C-section delivered case. Lower CD71⁺ erythroid cells were associated with a more pro-inflammatory milieu at the fetomaternal interface reflected by higher expression of inhibitory receptors on CD4⁺ T cells, higher frequency of monocytes and neutrophils. Furthermore, type of delivery impacted the gene expression profile in CD71⁺ erythroid cells. Finally, we found that C-section delivered child had > 20-fold higher FCP in his fecal sample at 12 wk of age.

CONCLUSION

Mode of delivery impacted immune cells profile in cord blood/placenta. In particular frequency of immunosuppressive CD71⁺ erythroid cells was reduced in C-section delivered newborn.

Cesarean delivery, preterm birth, and risk of food allergy: Nationwide Swedish cohort study of more than 1 million children

BACKGROUND

Little is known about early-life risk factors for food allergy in children.

OBJECTIVES

We examined the association between perinatal characteristics and future risk of food allergy in offspring.

METHODS

This nationwide Swedish cohort study of 1,086,378 children born in Sweden in 2001-2012 used prospectively recorded data from health care registers. Using Cox regression, we estimated hazard ratios (HRs) with 95% CIs for the association between perinatal characteristics (eg, cesarean delivery and preterm birth) and food allergy as defined by diagnoses in the National Patient Register, adjusting for infant sex and maternal factors (age at delivery, country of birth, parity, smoking, body mass index, and asthma/pulmonary disease).

RESULTS

During the 13-year follow-up, 26,732 (2.5%) children were given a diagnosis of food allergy. Food allergy was positively associated with cesarean delivery (HR, 1.21; 95% CI, 1.18-1.25), large for gestational age (HR, 1.15; 95% CI, 1.10-1.19), and low 5-minute Apgar score (HR, 1.22; 95% CI, 1.10-1.36) but negatively associated with very preterm birth (<32 weeks of gestation: HR, 0.74; 95% CI, 0.56-0.98). No association was found between food allergy and moderately preterm birth, low birth weight, or small for gestational age. Risk estimates were similar when the outcome was restricted to 2 records of diagnosed food allergy. In 1,000 children undergoing cesarean delivery, an extra 5 developed food allergy compared with the reference group, suggesting that 17% of food allergy in children born by means of cesarean delivery can be explained by this exposure (attributable fraction).

CONCLUSIONS

Cesarean delivery was associated with increased risk of food allergy, whereas very preterm birth decreased risk.