Egg-sensitised infants have elevated CD4+ effector memory T regulatory cells from birth.

BACKGROUND: IgE-mediated sensitisation to egg is common in infants. In some cases, the processes leading to egg sensitisation are established in early life, even before introduction to solid foods. The underlying mechanisms remain poorly understood. METHODS: We performed detailed immune cell phenotyping of peripheral blood mononuclear cells and determined in vitro cytokine responses following allergen specific and non-specific immune stimulation. To determine if unique immune profiles were linked to early-life egg sensitisation, we compared 92 infants at 4-6 months of age, with (EggCAP+, n = 41) and without (EggCAP-, n = 51) early egg sensitisation. Additionally, 47 cord blood samples were analysed. For a subset of participants (n = 39), matching cord blood mononuclear cells were assessed by flow cytometry to establish the impact of IgE sensitisation on immune developmental trajectories. RESULTS: EggCAP+ infants were found to exhibit a unique immune phenotype characterised by increased levels of circulating CD4+ T regulatory cells (Treg), CD4+ effector memory (EM) Treg and increased expression of the IgE receptor, FcεR1, on basophils. The increased CD4+ EM Treg profiles were already present in cord blood samples from EggCAP+ infants. A general Th2-skewing of the immune system was observed based on increased IL-13 production following phytohemagglutinin stimulation and by comparing immune developmental trajectories, EggCAP+ infants displayed an expansion of basophils and reduced levels of CD4- T cells compared to EggCAP- infants. CONCLUSIONS: Immunological profiles associated with egg sensitisation are detectable in infant circulation at 4-6 months of age and at birth. Understanding the immune mechanisms underlying early-life sensitisation could provide important insights for future food allergy prevention strategies.

Urinary Ferritin as a Noninvasive Means of Assessing Iron Status in Young Children.

BACKGROUND: Iron deficiency (ID) is the most common nutritional deficiency affecting young children. Serum ferritin concentration is the preferred biomarker for measuring iron status because it reflects iron stores; however, blood collection can be distressing for young children and can be logistically difficult. A noninvasive means to measure iron status would be attractive to either diagnose or screen for ID in young children. OBJECTIVES: This study aimed to determine the correlation between urinary and serum ferritin concentrations in young children; to determine whether correcting urinary ferritin for creatinine and specific gravity improves the correlation; and to determine a urine ferritin cut point to predict ID. METHODS: Validation study was conducted using paired serum and urine collected from 3-y-old children (n = 142) participating in a longitudinal birth cohort study: the ORIGINS project in Perth, Western Australia. We calculated the sensitivity, specificity, positive, and negative predictive values of urinary ferritin amount in identifying those with ID at the clinical cut point used by the World Health Organization (serum ferritin concentration of <12 ng/mL). RESULTS: Urine ferritin, corrected for creatinine, correlated moderately with serum ferritin [r = 0.53 (0.40-0.64)] and performed well in predicting those with ID (area under the curve: 0.85; 95% confidence interval: 0.75, 0.94). Urine ferritin <2.28 ng/mg creatinine was sensitive (86%) and specific (77%) in predicting ID and had a high negative predictive value of 97%; however, the positive predictive value was low (40%) owing to the low prevalence of ID in the sample (16%). CONCLUSIONS: Urine ferritin shows good diagnostic performance for ID. This noninvasive biomarker maybe a useful screening tool to exclude ID in healthy young children; however, further research is needed in other populations.

Maternal serum unmetabolized folic acid concentration following multivitamin and mineral supplementation with or without folic acid after 12 weeks gestation: A randomized controlled trial.

Pregnant women are advised to take folic acid (FA) supplements before conception and during the first trimester of pregnancy. Many women continue FA supplementation throughout pregnancy, and concerns have been raised about associations between excessive FA intake and adverse maternal and child health outcomes. Unmetabolized folic acid (UMFA) is found in serum after high FA intakes and is proposed as a biomarker for excessive FA intake. We aimed to determine if removing FA from prenatal micronutrient supplements after 12 weeks of pregnancy reduces serum UMFA concentrations at 36 weeks gestation. In this double-blind, randomized controlled trial conducted in South Australia, 103 women with a singleton pregnancy were randomly assigned at 12-16 weeks gestation to take a micronutrient supplement containing no FA or 800 µg/day FA from enrollment until 36 weeks gestation. Ninety women (0 µg/day FA n = 46; 800 µg/day FA n = 44) completed the study. Mean, UMFA concentration was lower in the women randomized to the 0 µg/day group compared to the 800 µg/day FA group, 0.6 ± 0.7 and 1.4 ± 2.7 nmol/L, respectively. The adjusted mean difference (95% CI) in UMFA between the groups was [-0.85 (-1.62, -0.08) nmol/L, p = 0.03]. Maternal serum and red blood cell folate concentrations were lower in the 0 µg/day FA group than in the 800 µg/day group (median 23.2 vs. 49.3 and 1335 vs. 1914 nmol/L, respectively; p < 0.001). Removing FA at 12-16 weeks gestation from prenatal micronutrient supplements reduced the concentration of UMFA at 36 weeks gestation.

Feasibility and safety of introducing cashew nut spread in infant diets-A randomized trial.

BACKGROUND: To reduce peanut allergy prevalence, infant feeding guidelines now recommend introducing peanuts in an age-appropriate form (such as peanut butter) as part of complementary feeding. However, due to a lack of randomized trial evidence, most infant feeding and food allergy prevention guidelines do not include tree nuts. The aims of this trial were to determine safety and feasibility of dosage consumption recommendations for infant cashew nut spread introduction. METHODS: This is a parallel, three-arm (1:1:1 allocation), single-blinded (outcome assessors), randomized controlled trial. General population term infants were randomized at 6-8 months of age to either a one teaspoon (Intervention 1 n = 59) or increasing dosage regime of one teaspoon at 6-7 months, two teaspoons at 8-9 months, and three teaspoons from 10 months of age onwards (Intervention 2 n = 67) cashew nut spread, both three times per week, or no specific advice on cashew introduction (Control n = 70). At 1 year of age, food challenge proven IgE-mediated cashew nut allergy was assessed. RESULTS: Compliance in Intervention 1 (92%) was higher than Intervention 2 (79%), p = .04. Only one infant had delayed (at 5 h) facial swelling and eczema flare to cashew introduction at 6.5 months, but no cashew allergy at 1 year. Only one infant (Control) had cashew allergy at 1 year, and this infant had not been introduced to cashew prior to 12 months of age. CONCLUSION: Regular infant consumption of one teaspoon of cashew nut spread three times per week from 6 to 8 months of age was found to be feasible and safe.

Longitudinal egg-specific regulatory T- and B-cell development: Insights from primary prevention clinical trials examining the timing of egg introduction.

BACKGROUND: Egg allergy affects almost 1 in 10 Australian infants. Early egg introduction has been associated with a reduced risk in developing egg allergy; however, the immune mechanisms underlying this protection remain unclear. OBJECTIVE: To examine the role of regulatory immune cells in tolerance induction during early egg introduction. METHODS: Cryopreserved peripheral blood mononuclear cells (PBMC) were obtained from infants from 2 randomized controlled trials of early introduction of egg for the primary prevention of egg allergy; BEAT (at 12 months, n = 42) and STEP (at 5 months n = 82; 12 months n = 82) study cohorts. In vitro ovalbumin-stimulated PBMC were analyzed by flow cytometry for presence of ovalbumin-specific regulatory T cells, using activation markers, FoxP3, and IL-10 expression. Ovalbumin-specific regulatory B cells were identified by co-expression of fluorescence-conjugated ovalbumin and IL-10. RESULTS: Specific, age-dependent expansion of ovalbumin-specific regulatory T cells was only observed in infants who (a) had early egg introduction and (b) did not have egg allergy at 12 months. This expansion was blunted or impaired in children who did not undergo early egg introduction and in those with clinical egg allergy at 12 months. Infants with egg allergy at 12 months of age also had reduced frequency of ovalbumin-specific regulatory B cells compared to egg-tolerant infants. CONCLUSION: Early egg introduction and clinical tolerance to egg were associated with expansion of ovalbumin-specific T and B regulatory cells, which may be an important developmental process for tolerance acquisition to food allergens.

Maternal Late-Pregnancy Serum Unmetabolized Folic Acid Concentrations Are Not Associated with Infant Allergic Disease: A Prospective Cohort Study.

BACKGROUND: The increase in childhood allergic disease in recent decades has coincided with increased folic acid intakes during pregnancy. Circulating unmetabolized folic acid (UMFA) has been proposed as a biomarker of excessive folic acid intake. OBJECTIVE: We aimed to determine if late-pregnancy serum UMFA and total folate concentrations were associated with allergic disease risk in the offspring at 1 y of age in a population at high risk of allergy. METHODS: The cohort consisted of 561 mother-infant pairs from Western Australia. To be eligible the infant had to have a first-degree relative (mother, father, or sibling) with a history of medically diagnosed allergic disease. Maternal venous blood was collected between 36 and 40 wk of gestation. Serum UMFA was measured by LC-tandem MS. Serum total folate was determined using a microbiological method with chloramphenicol-resistant Lactobacillus rhamnosus as the test organism, and was collected between 36 and 40 wk of gestation. UMFA concentrations were measured by tandem MS using stable isotope dilution; folate concentrations were determined using the microbiological method with standardized kits. Infant allergic disease outcomes of medically diagnosed eczema, steroid-treated eczema, atopic eczema, IgE-mediated food allergy, allergen sensitization, and medically diagnosed wheeze were assessed at 1 y of age. RESULTS: Median (IQR) concentrations for UMFA and serum folate were 1.6 (0.6-4.7) and 53.2 (32.6-74.5) nmol/L, respectively. Of the infants, 34.6% had medically diagnosed eczema, 26.4% allergen sensitization, and 14.9% had an IgE-mediated food allergy. In both adjusted and unadjusted models there was little evidence of association between UMFA or serum folate and any of the infant allergy outcomes. CONCLUSIONS: In this cohort of children at high risk of allergic disease there was no association between maternal UMFA or serum folate concentrations measured in late pregnancy and allergic disease outcomes at 1 y of age.

Lower Cord Blood IL-17 and IL-25, but Not Other Epithelial Cell-Derived Cytokines Are Associated with Atopic Dermatitis in Infancy.

BACKGROUND: There is a growing need for early biomarkers that may predict the development of atopic dermatitis (AD). As alterations in skin barrier may be a primary event in disease pathogenesis, epithelial cell (EC) cytokines expression patterns may be a potential biomarker in early life to target allergy preventive strategies towards "at-risk" infants. OBJECTIVES: The aim of this longitudinal investigation was to examine from birth over the course of infancy levels of the EC cytokines: thymic stromal lymphopoietin (TSLP), interleukin (IL)-33, IL-25, and IL-17 in infants at high-risk of AD due to maternal atopy. METHOD: We collected (n = 31) cord blood samples from atopic mothers and followed up their infants at 4-6 and 12 months of age for collection of peripheral venous blood samples and diagnosis of AD. TSLP concentration was measured by ELISA after acetone precipitation of the samples. IL-33, IL-25, and IL-17 levels were measured by Luminex. RESULTS: Seven infants who developed AD had lower levels of IL-25 and IL-17 at birth compared to the 24 infants who did not develop AD by 12 months of age. CONCLUSIONS: Lower cord blood levels of IL-17 and IL-25, but not other EC cytokines, were associated with the onset of AD during infancy. Our results highlight that the in-utero period appears critical, and potential maternal influences on cord blood EC-derived cytokine concentrations requires further exploration.

A role for early oral exposure to house dust mite allergens through breast milk in IgE-mediated food allergy susceptibility.

BACKGROUND: Successful prevention of food allergy requires the identification of the factors adversely affecting the capacity to develop oral tolerance to food antigen in early life. OBJECTIVES: This study sought to determine whether oral exposure to Dermatophagoides pteronyssinus through breast milk affects gut mucosal immunity with long-term effects on IgE-mediated food allergy susceptibility. METHODS: Gut immunity was explored in 2-week-old mice breast-fed by mothers exposed to D pteronyssinus, protease-inactivated D pteronyssinus, or to PBS during lactation. We further analyzed oral tolerance to a bystander food allergen, ovalbumin (OVA). In a proof-of-concept study, Der p 1 and OVA levels were determined in 100 human breast milk samples and the association with prevalence of IgE-mediated egg allergy at 1 year was assessed. RESULTS: Increased permeability, IL-33 levels, type 2 innate lymphoid cell activation, and Th2 cell differentiation were found in gut mucosa of mice nursed by mothers exposed to D pteronyssinus compared with PBS. This pro-Th2 gut mucosal environment inhibited the induction of antigen-specific FoxP3 regulatory T cells and the prevention of food allergy by OVA exposure through breast milk. In contrast, protease-inactivated D pteronyssinus had no effect on offspring gut mucosal immunity. Based on the presence of Der p 1 and/or OVA in human breast milk, we identified groups of lactating mothers, which mirror the ones found in mice to be responsible for different egg allergy risk. CONCLUSIONS: This study highlights an unpredicted potential risk factor for the development of food allergy, that is, D pteronyssinus allergens in breast milk, which disrupt gut immune homeostasis and prevents oral tolerance induction to bystander food antigen through their protease activity.

In infants with sufficient vitamin D status at birth, vitamin D supplementation does not impact immune development.

BACKGROUND: Low vitamin D levels have been associated with allergic diseases. Vitamin D has potent immunomodulatory properties, but the mechanisms remain unclear. We have investigated the effect of oral vitamin D supplementation on circulating immune cell phenotypes in infants. METHOD: A double-blinded randomised controlled trial was conducted to investigate the effect of oral vitamin D supplementation (400 IU/d) on eczema and immune development. A subset of 78 infants was included in this analysis. Phenotypic analysis of immune cell subsets was performed using flow cytometry. RESULTS: Vitamin D supplementation resulted in median 25(OH)D levels of 80.5 vs 59.5 nmol/L in the placebo group at 3 months of age (P = .002) and 87.5 vs 77 nmol/L at 6 months of age (P = .08). We observed significant changes in immune cell composition from birth (cord blood) to 6 months of age. Vitamin D supplementation did not impact these changes, nor did immune cell composition correlate with plasma 25(OH)D levels. Through exploratory analysis, we identified possible associations with eczema development and increased abundance of naïve CD4- T cells at birth, as well as associations with basophils, iNKT and central memory CD4+ T cells, and altered expression patterns of IgE receptor (FcεR1) on monocytes and dendritic cells with eczema at 6 months. CONCLUSIONS: Vitamin D supplementation in infants who were vitamin D sufficient at birth did not affect developmental changes in immune cells during the first 6 months of life. However, immune cell profiles at birth and at 6 months of age were associated with early life eczema.

Dietary factors during pregnancy and atopic outcomes in childhood: A systematic review from the European Academy of Allergy and Clinical Immunology.

RATIONALE: Allergic diseases are an increasing public health concern, and early life environment is critical to immune development. Maternal diet during pregnancy has been linked to offspring allergy risk. In turn, maternal diet is a potentially modifiable factor, which could be targeted as an allergy prevention strategy. In this systematic review, we focused on non-allergen-specific modifying factors of the maternal diet in pregnancy on allergy outcomes in their offspring. METHODS: We undertook a systematic review of studies investigating the association between maternal diet during pregnancy and allergic outcomes (asthma/wheeze, hay fever/allergic rhinitis/seasonal allergies, eczema/atopic dermatitis (AD), food allergies, and allergic sensitization) in offspring. Studies evaluating the effect of food allergen intake were excluded. We searched three bibliographic databases (MEDLINE, EMBASE, and Web of Science) through February 26, 2019. Evidence was critically appraised using modified versions of the Cochrane Collaboration Risk of Bias tool for intervention trials and the National Institute for Clinical Excellence methodological checklist for cohort and case-control studies and meta-analysis performed from RCTs. RESULTS: We identified 95 papers: 17 RCTs and 78 observational (case-control, cross-sectional, and cohort) studies. Observational studies varied in design and dietary intakes and often had contradictory findings. Based on our meta-analysis, RCTs showed that vitamin D supplementation (OR: 0.72; 95% CI: 0.56-0.92) is associated with a reduced risk of wheeze/asthma. A positive trend for omega-3 fatty acids was observed for asthma/wheeze, but this did not reach statistical significance (OR: 0.70; 95% CI: 0.45-1.08). Omega-3 supplementation was also associated with a non-significant decreased risk of allergic rhinitis (OR: 0.76; 95% CI: 0.56-1.04). Neither vitamin D nor omega-3 fatty acids were associated with an altered risk of AD or food allergy. CONCLUSIONS: Prenatal supplementation with vitamin D may have beneficial effects for prevention of asthma. Additional nutritional factors seem to be required for modulating the risk of skin and gastrointestinal outcomes. We found no consistent evidence regarding other dietary factors, perhaps due to differences in study design and host features that were not considered. While confirmatory studies are required, there is also a need for performing RCTs beyond single nutrients/foods.

Low allergen content of commercial baby foods.

AIM: Introduction of allergenic solid foods, especially peanut and hen's egg reduces the risk of food allergy development in early childhood. Ideally, parents will offer their infants home-prepared foods; however, many rely on the availability of convenient ready to purchase infant foods. This audit aimed to assess the major food allergen content of commercial infant foods. METHODS: Infant foods available for sale in 2019 in Australia were the focus of this audit. The major food allergens investigated were peanut, tree nuts, hen's egg, cows milk, wheat, fish, shellfish, soy, sesame and lupin. Websites of infant food manufacturers and major supermarkets were used to identify ingredient lists of infant foods available for purchase. Where ingredients listings were unavailable this information was sourced directly from the product labels in the supermarket. RESULTS: Fourteen companies were identified, manufacturing over 251 foods specifically for the infants aged less than 1 year of age. Although there were many choices available containing wheat (27 products) and cows milk proteins (73 products), none contained peanut, tree nuts, sesame, shellfish or lupin. CONCLUSIONS: Despite infant feeding advice encouraging early introduction to food allergens, of 251 commercial baby foods surveyed only 1% contained egg and none contained peanut, the most common food allergies in young Australian infants. This low food allergen content may be disadvantageous for infants fed mostly commercial infant foods as they are unlikely to be exposed to sufficient amounts of the major food allergens on a regular basis during infancy.

Direct infant UV light exposure is associated with eczema and immune development.

BACKGROUND: Suboptimal vitamin D levels during critical periods of immune development have emerged as an explanation for higher rates of allergic diseases associated with industrialization and residing at higher latitudes. OBJECTIVE: We sought to determine the effects of early postnatal vitamin D supplementation on infant eczema and immune development. METHODS: By using a double-blind randomized controlled trial, newborn infants were randomized to receive vitamin D supplementation (400 IU/d) or a placebo until 6 months of age. Some infants also wore personal UV dosimeters to measure direct UV light (290-380 nm) exposure. Infant vitamin D levels were measured at 3 and 6 months of age. Eczema, wheeze, and immune function outcomes were assessed at 6 months of age. RESULTS: At 3 (P < .01) and 6 (P = .02) months of age, vitamin D levels were greater for the vitamin D-supplemented group than the placebo group, but there was no difference in eczema incidence between groups. Infants with eczema were found to have had less UV light exposure (median, 555 Joules per square meter [J/m2; interquartile range, 322-1210 J/m2]) compared with those without eczema (median, 998 J/m2 [interquartile range, 676-1577 J/m2]; P = .02). UV light exposure was also inversely correlated with IL-2, GM-CSF, and eotaxin production to Toll-like receptor ligands. CONCLUSION: This study is the first to demonstrate an association between greater direct UV light exposures in early infancy with lower incidence of eczema and proinflammatory immune markers by 6 months of age. Our findings indicate that UV light exposure appears more beneficial than vitamin D supplementation as an allergy prevention strategy in early life.

Randomized controlled trial of early regular egg intake to prevent egg allergy.

BACKGROUND: The ideal age to introduce egg into the infant diet has been debated for the past 2 decades in the context of rising rates of egg allergy. OBJECTIVE: We sought to determine whether regular consumption of egg protein from age 4 to 6 months reduces the risk of IgE-mediated egg allergy in infants with hereditary risk, but without eczema. METHODS: Infants aged 4 to 6 months were randomly allocated to receive daily pasteurized raw whole egg powder (n = 407) or a color-matched rice powder (n = 413) to age 10 months. All infants followed an egg-free diet and cooked egg was introduced to both groups at age 10 months. The primary outcome was IgE-mediated egg allergy defined by a positive pasteurized raw egg challenge and egg sensitization at age 12 months. RESULTS: There was no difference between groups in the percentage of infants with IgE-mediated egg allergy (egg 7.0% vs control 10.3%; adjusted relative risk, 0.75; 95% CI, 0.48-1.17; P = .20). A higher proportion of participants in the egg group stopped taking the study powder because of a confirmed allergic reaction (25 of 407 [6.1%] compared with 6 of 413 [1.5%]). Egg-specific IgG4 levels were substantially higher in the egg group at 12 months (median, 1.22 mgA/L vs control 0.07 mgA/L; P < .0001). CONCLUSIONS: We found no evidence that regular egg intake from age 4 to 6 months substantially alters the risk of egg allergy by age 1 year in infants who are at hereditary risk of allergic disease and had no eczema symptoms at study entry.

Maternal dietary intake in pregnancy and lactation and allergic disease outcomes in offspring.

As the prevalence of allergic disease dramatically rises worldwide, prevention strategies are increasingly being considered. Given the potential modulatory effect of nutritional factors on disease, altering maternal diet during pregnancy and/or lactation has been considered in preventing allergic disease in offspring. Although there are a number of observational studies that have examined possible associations between maternal diet and allergic outcomes in offspring, interventional trials are limited. Furthermore, there is a paucity of studies that have prospectively studied maternal dietary intake as well as measuring maternal and infant biologic samples (blood, urine, breast milk) and their relation to allergic outcomes in infants. There is also a particular need to define terminology such as 'fruit and vegetables intake', 'healthy diet', and 'diet diversity' in order to make studies comparable. In this review, we discuss current evidence of maternal dietary factors during pregnancy and/or lactation that may play a role in the offspring developing allergic disease, including factors such as overall dietary intake patterns, specific whole food consumption (fish, fruit and vegetables, and common allergic foods), and individual immunomodulatory nutrient intakes. Additionally, we discuss the limitations of previous studies and propose improvements to study design for future investigation.

Nutritional approaches for the primary prevention of allergic disease: An update.

The dramatic rise in early childhood allergic diseases indicates the specific vulnerability of the immune system to early life environmental changes. Dietary changes are at the centre of lifestyle changes that underpin many modern inflammatory and metabolic diseases, and therefore are an essential element of prevention strategies. Although modern dietary changes are complex and involve changing patterns of many nutrients, there is also an interest in the early life effects of specific nutrients including polyunsaturated fatty acids, oligosaccharides (soluble fibre), antioxidants, folate and other vitamins that have documented effects on immune function as well as metabolism. A better understanding of nutritional programming of immune health, nutritional epigenetics and the biological processes sensitive to nutritional exposures in early life may lead to dietary strategies that provide more tolerogenic conditions during early immune programming and reduce the burden of many inflammatory diseases, not just allergy.

Early regular egg exposure in infants with eczema: A randomized controlled trial.

BACKGROUND: Observational studies suggest that early regular ingestion of allergenic foods might reduce the risk of food allergy. OBJECTIVE: We sought to determine whether early regular oral egg exposure will reduce subsequent IgE-mediated egg allergy in infants with moderate-to-severe eczema. METHODS: In a double-blind, randomized controlled trial infants were allocated to 1 teaspoon of pasteurized raw whole egg powder (n = 49) or rice powder (n = 37) daily from 4 to 8 months of age. Cooked egg was introduced to both groups after an observed feed at 8 months. The primary outcome was IgE-mediated egg allergy at 12 months, as defined based on the results of an observed pasteurized raw egg challenge and skin prick tests. RESULTS: A high proportion (31% [15/49]) of infants randomized to receive egg had an allergic reaction to the egg powder and did not continue powder ingestion. At 4 months of age, before any known egg ingestion, 36% (24/67) of infants already had egg-specific IgE levels of greater than 0.35 kilounits of antibody (kUA)/L. At 12 months, a lower (but not significant) proportion of infants in the egg group (33%) were given a diagnosis of IgE-mediated egg allergy compared with the control group (51%; relative risk, 0.65; 95% CI, 0.38-1.11; P = .11). Egg-specific IgG4 levels were significantly (P < .001) greater in the egg group at both 8 and 12 months. CONCLUSION: Induction of immune tolerance pathways and reduction in egg allergy incidence can be achieved by early regular oral egg exposure in infants with eczema. Caution needs to be taken when these high-risk infants are first exposed to egg because many have sensitization already by 4 months of age.

Associations between sun exposure, skin pH, and epidermal permeability in pregnancy: A longitudinal observational study.

Little is known about how sun exposure may affect the maternal skin barrier during pregnancy when many hormonal and physiological changes occur. In this longitudinal observational study, 50 pregnant women were recruited at 18-24 weeks' gestation, 25 in summer-autumn, and 25 in winter-spring. At three time points in pregnancy at 18-24, 28-30, and 36-38 weeks' gestation, participants completed a validated sun exposure questionnaire and had skin permeability and surface pH measured on the volar forearm. We identified an association between increased sun exposure and increased skin permeability at 18-24 weeks' gestation (ß = 0.85, p = 0.01). Lower transepidermal water loss (decreased skin permeability), mean = 12.1 (SD = 5.1) at 28-30 weeks' gestation was observed, compared to mean = 12.6 (SD = 4.0) at 18-24 weeks' and mean = 13.7 (SD = 8.5) at 36-38 weeks' gestation (n = 27, ß = -1.83, p = 0.007). Higher skin pH readings, mean = 5.80 (SD = 0.58) were found at 28-30 weeks' gestation, compared to mean = 5.25 (SD = 0.62) at 18-24 weeks' and mean = 5.47 (SD = 0.57) at 36-38 weeks' gestation (n = 27, ß = 0.40, p = 0.004). These gestational fluctuations remained after adjusting for Fitzpatrick skin type, season, and sun exposure. We observed gestational fluctuations in both skin permeability and skin pH, with 28-30 weeks' gestation being a significant point of difference compared to mid- and late-pregnancy periods.