Maternal characteristics and pregnancy outcomes in the NICE birth cohort: an assessment of self-selection bias

Toxic metals and essential trace elements in placenta and their relation to placental function

INTRODUCTION

Placental function is essential for fetal development, but it may be susceptible to malnutrition and environmental stressors.

OBJECTIVE

To assess the impact of toxic and essential trace elements in placenta on placental function.

METHODS

Toxic metals (cadmium, lead, mercury, cobalt) and essential elements (copper, manganese, zinc, selenium) were measured in placenta of 406 pregnant women in northern Sweden using ICP-MS. Placental weight and birth weight were obtained from hospital records and fetoplacental weight ratio was used to estimate placental efficiency. Placental relative telomere length (TL) and mitochondrial DNA copy number (mtDNAcn) were determined by quantitative PCR (n = 285). Single exposure-outcome associations were evaluated using linear or spline regression, and joint associations and interactions with Bayesian kernel machine regression (BKMR), all adjusted for sex, maternal smoking, and age or BMI.

RESULTS

Median cadmium, mercury, lead, cobalt, copper, manganese, zinc, and selenium concentrations in placenta were 3.2, 1.8, 4.3, 2.3, 1058, 66, 10626, and 166 μg/kg, respectively. In the adjusted regression, selenium (>147 μg/kg) was inversely associated with placental weight (B: -158; 95 % CI: -246, -71, per doubling), as was lead at low selenium (B: -23.6; 95 % CI: -43.2, -4.0, per doubling). Manganese was positively associated with placental weight (B: 41; 95 % CI: 5.9, 77, per doubling) and inversely associated with placental efficiency (B: -0.01; 95 % CI: -0.019, -0.004, per doubling). Cobalt was inversely associated with mtDNAcn (B: -11; 95 % CI: -20, -0.018, per doubling), whereas all essential elements were positively associated with mtDNAcn, individually and joint.

CONCLUSION

Among the toxic metals, lead appeared to negatively impact placental weight and cobalt decreased placental mtDNAcn. Joint essential element concentrations increased placental mtDNAcn. Manganese also appeared to increase placental weight, but not birth weight. The inverse association of selenium with placental weight may reflect increased transport of selenium to the fetus in late gestation.

Short-chain fatty acids (SCFA) in infants' plasma and corresponding mother's milk and plasma in relation to subsequent sensitisation and atopic disease

BACKGROUND

Short-chain fatty acids (SCFAs) in intestinal contents may influence immune function, while less is known about SCFAs in blood plasma. The aims were to investigate the relation between infants' and maternal plasma SCFAs, as well as SCFAs in mother's milk, and relate SCFA concentrations in infant plasma to subsequent sensitisation and atopic disease.

METHODS

Infant plasma (N = 148) and corresponding mother's milk and plasma were collected four months postpartum. Nine SCFA (formic, acetic, propionic, isobutyric, butyric, succinic, valeric, isovaleric, and caproic acid) were analysed by UPLC-MS. At 12 months of age, atopic disease was diagnosed by a pediatric allergologist, and sensitisation was measured by skin prick test. All families participated in the Swedish birth cohort NICE (Nutritional impact on Immunological maturation during Childhood in relation to the Environment).

FINDINGS

Infants with sensitisation, atopic eczema, or food allergy had significantly lower concentrations of five, three, and two SCFAs, respectively, in plasma at four months. Logistic regressions models showed significant negative associations between formic, succinic, and caproic acid and sensitisation [ORadj (95% CI) per SD: 0.41 (0.19-0.91); 0.19 (0.05-0.75); 0.25 (0.09-0.66)], and between acetic acid and atopic eczema [0.42 (0.18-0.95)], after adjusting for maternal allergy. Infants' and maternal plasma SCFA concentrations correlated strongly, while milk SCFA concentrations were unrelated to both. Butyric and caproic acid concentrations were enriched around 100-fold, and iso-butyric and valeric acid around 3-5-fold in mother's milk, while other SCFAs were less prevalent in milk than in plasma.

INTERPRETATION

Butyric and caproic acid might be actively transported into breast milk to meet the needs of the infant, although mechanistic studies are needed to confirm this. The negative associations between certain SCFAs on sensitisation and atopic disease adds to prior evidence regarding their immunoregulatory potential.

FUNDING

Swedish Research Council (Nr. 2013-3145, 2019-0137 and 2023-02217 to A-S.S.), Swedish Research Council for Health, Working Life and Welfare FORTE, Nr 2018-00485 to A.W.), The Swedish Asthma and Allergy Association's Research Fund (2020-0020 to A.S.).

Associations of the placental metabolome with immune maturation up to one year of age in the Swedish NICE-cohort

INTRODUCTION

Allergies and other immune-mediated diseases are thought to result from incomplete maturation of the immune system early in life. We previously showed that infants' metabolites at birth were associated with immune cell subtypes during infancy. The placenta supplies the fetus with nutrients, but may also provide immune maturation signals.

OBJECTIVES

To examine the relationship between metabolites in placental villous tissue and immune maturation during the first year of life and infant and maternal characteristics (gestational length, birth weight, sex, parity, maternal age, and BMI).

METHODS

Untargeted metabolomics was measured using Liquid Chromatography-Mass Spectrometry. Subpopulations of T and B cells were measured using flow cytometry at birth, 48 h, one, four, and 12 months. Random forest analysis was used to link the metabolomics data with the T and B cell sub populations as well as infant and maternal characteristics.

RESULTS

Modest associations (Q2 = 0.2-0.3) were found between the placental metabolome and kappa-deleting recombination excision circles (KREC) at birth and naïve B cells and memory T cells at 12 months. Weak associations were observed between the placental metabolome and sex and parity. Still, most metabolite features of interest were of low intensity compared to associations previously found in cord blood, suggesting that underlying metabolites were not of placental origin.

CONCLUSION

Our results indicate that metabolomic measurements of the placenta may not effectively recognize metabolites important for immune maturation.

Higher free testosterone in the third trimester was associated with lower abdominal circumference at birth in boys: Odense child cohort

OBJECTIVE

To investigate associations between maternal testosterone status and offspring birth anthropometrics.

DESIGN

Population-based prospective cohort study.

SETTING

University Hospital.

POPULATION

1486 mother-child dyads from Odense Child Cohort.

METHODS

Maternal blood samples were collected at gestational weeks 27-30 and free testosterone (FT) levels were calculated using the Vermeulen equation from total testosterone (TT) analysed by mass spectrometry and sex hormone binding globulin. Associations between FT or TT levels and birth anthropometrics were analysed with multiple linear regression models according to offspring sex with adjustment for maternal age, parity, smoking and educational level. Analyses were repeated with polycystic ovary syndrome as exposure for offspring birth anthropometrics.

MAIN OUTCOME MEASURES

Offspring birth weight (BW), birth length, abdominal and head circumferences.

RESULTS

Maternal mean (SD) age was 30.2 (4.5) years and pre-pregnancy body mass index was 23.5 (5.3) kg/m2 . In boys (n = 787), higher FT was associated with lower birth weight (adjusted doubling constant = -65.53, P = 0.010), shorter birth length (adjusted doubling constant = -0.43, P < 0.001), and lower abdominal circumference (adjusted doubling constant = -0.39, P < 0.001); Higher TT was associated with lower abdominal circumference (adjusted doubling constant = -0.25, P = 0.028). In girls, no associations were found between maternal FT or TT and offspring anthropometrics.

CONCLUSIONS

Higher maternal free testosterone exposure was linked to reduced birth weight, length and abdominal circumference in boys, whereas girls were not susceptible to maternal testosterone exposure.

Associations of gestational and early-life exposure to toxic metals and fluoride with a diagnosis of food allergy or atopic eczema at 1 year of age

Studies have indicated that early-life exposure to toxic metals and fluoride affects the immune system, but evidence regarding their role in allergic disease development is scarce. We aimed to evaluate the relations of exposure to such compounds in 482 pregnant women and their infants (4 months of age) with food allergy and atopic eczema diagnosed by a paediatric allergologist at 1 year of age within the Swedish birth-cohort NICE (Nutritional impact on Immunological maturation during Childhood in relation to the Environment). Urinary cadmium and erythrocyte cadmium, lead, and mercury concentrations were measured by inductively coupled plasma mass spectrometry (ICP-MS), urinary inorganic arsenic metabolites by ICP-MS after separation by ion exchange chromatography, and urinary fluoride by an ion-selective electrode. The prevalence of food allergy and atopic eczema was 8 and 7%, respectively. Gestational urinary cadmium, reflecting chronic exposure, was associated with increased odds of infant food allergy (OR [95% CI]: 1.34 [1.09, 1.66] per IQR [0.08 μg/L]). Both gestational and infant urinary fluoride were associated, albeit at a statistically non-significant level, with increased atopic eczema odds (1.48 [0.98, 2.25], 1.36 [0.95, 1.95], per doubling, respectively). By contrast, gestational and infant erythrocyte lead was associated with decreased odds of atopic eczema (0.48 [0.26, 0.87] per IQR [6.6 μg/kg] and 0.38 [0.16, 0.91] per IQR [5.94 μg/kg], respectively), and infant lead with decreased odds of food allergy (0.39 [0.16, 0.93] per IQR [5.94 μg/kg]). Multivariable adjustment had marginal impact on the estimates above. After additional adjustment for fish intake biomarkers, the methylmercury associated atopic-eczema odds were considerably increased (1.29 [0.80, 2.06] per IQR [1.36 μg/kg]). In conclusion, our results indicate that gestational cadmium exposure might be associated with food allergy at 1 year of age and, possibly, early-life exposure to fluoride with atopic eczema. Further prospective and mechanistic studies are needed to establish causality.

Association of maternal urinary fluoride concentrations during pregnancy with size at birth and the potential mediation effect by maternal thyroid hormones: The Swedish NICE birth cohort

BACKGROUND

Observational studies have indicated that elevated maternal fluoride exposure during pregnancy may impair child neurodevelopment but a potential impact on birth outcomes is understudied.

OBJECTIVES

To evaluate the impact of gestational fluoride exposure on birth outcomes (birth size and gestational age at birth) and to assess the potential mediating role of maternal thyroid hormones.

METHODS

We studied 583 mother-child dyads in the NICE cohort in northern Sweden. Maternal fluoride exposure was assessed by measuring urinary concentrations at late pregnancy (median: 29th gestational week) using an ion selective electrode. Plasma levels of free and total thyroxine (fT4, tT4) and triiodothyronine (fT3, tT3), and thyroid stimulating hormone (TSH) were measured with electrochemiluminescence immunoassays. The infant's weight, length, head circumference, and gestational age at birth were extracted from hospital records.

RESULTS

Median urinary fluoride concentration was 0.71 mg/L (5th-95th percentile 0.31-1.9 mg/L; specific gravity adjusted). In multivariable-adjusted regression models, every 1 mg/L increase of maternal urinary fluoride was associated with a mean increase in birth weight by 84 g (95%CI: 30, 138), length by 0.41 cm (95%CI: 0.18, 0.65), head circumference by 0.3 cm (95%CI: 0.1, 0.4), and with increased odds of being born large for gestational age (OR = 1.39, 95%CI: 1.03, 1.89). Every 1 mg/L increase of maternal urinary fluoride was also associated with a mean increase of the plasma fT3:fT4 ratio (B = 0.007, 95%CI: 0.000, 0.014), but not with the hormones or TSH. In mediation analyses, the maternal fT3:fT4 ratio did not explain the urinary fluoride-birth size relationships.

DISCUSSION

Gestational urinary fluoride concentrations were associated with increased size at birth and even with increased odds of being born large for gestational age. The fluoride-related associations with increased size at birth were not explained by changes in maternal thyroid hormone levels.

Educational attainment and offspring birth weight: A bidirectional Mendelian randomization study

Background: The association between educational attainment (EA) and offspring birth weight (BW) has been reported by several traditional epidemiological studies. However, evidence for this association tends to be mixed and confounded. This study aimed to investigate the causal association between EA of parents and offspring BW. Methods: Here, we carried out a two-sample bidirectional Mendelian randomization (MR) analysis to examine the causal association between EA of males (n = 131,695) and females (n = 162,028) and offspring BW using genetic instruments. Summary statistics of EA associated single nucleotide polymorphisms (SNPs) were extracted from a GWAS incorporating 293,723 individuals of European descent performed by the Social Science Genetic Association Consortium (SSGAC), and the effects of these SNPs on offspring BW were estimated using a GWAS meta-analysis of 86,577 participants of European descent from 25 studies. Univariable MR analyses were conducted using the inverse-variance weighted (IVW) method and four other methods. Further sensitivity analyses were carried out to test the viability of the results. Multivariable MR was used to examine the confounders between the exposure and outcome. Results: The result shows evidence that the offspring BW is positively causally affected by female EA. Each one standard deviation (SD) increase in female EA was associated with 0.24 SD higher of offspring BW (95% confidence interval [CI], 0.10 to 0.37, p < 0.001 for the IVW method). Similarly, change in offspring BW was 0.21 SD (95% CI: 0.07 to 0.34, p = 2.82 × 10-3) per one SD higher in male EA. No causal effect of BW on EA was found by any of the five methods. The causal association between female EA and offspring BW maintained after adjusting for alcoholic drinks per week and BMI. The effect of male EA on offspring BW was attenuated when we adjusted for BMI and alcoholic drinks per week using multivariable MR analysis. Conclusion: Our study indicated that female EA is positively causally associated with offspring BW. The association between male EA and offspring BW may be confounded by alcoholic drinks per week and BMI.

Infant Iodine and Selenium Status in Relation to Maternal Status and Diet During Pregnancy and Lactation

Iodine and selenium are essential trace elements. Recent studies indicate that pregnant and lactating women often have insufficient intake of iodine and selenium, but the impact on fetal and infant status is unclear. Here, we assessed iodine and selenium status of infants in relation to maternal intake and status of these trace elements in the birth cohort NICE, conducted in northern Sweden (n = 604). Iodine was measured in urine (UIC) in gestational week 29, and in breast milk and infant urine 4 months postpartum, while selenium was measured in maternal plasma and erythrocytes in gestational week 29, and in breast milk and infant erythrocytes 4 months postpartum, in both cases using ICP-MS. Maternal intake was assessed with semi-quantitative food frequency questionnaires in gestational week 34 and at 4 months postpartum. The median intake of iodine and selenium during pregnancy (98 and 40 μg/d, respectively) and lactation (108 and 39 μg/d, respectively) was below recommended intakes, reflected in insufficient status (median UIC of 113 μg/L, median plasma selenium of 65 μg/L). Also, breast milk concentrations (median iodine 77 μg/L, median selenium 9 μg/L) were unlikely to meet infant requirements. Median UIC of the infants was 114 μg/L and median erythrocyte selenium 96 μg/kg, both similar to the maternal concentrations. Infant UIC correlated strongly with breast milk levels (rho = 0.64, p < 0.001). Their erythrocyte selenium correlated with maternal erythrocyte selenium in pregnancy (rho = 0.38, p < 0.001), but not with breast milk selenium, suggesting formation of prenatal reserves. Our results indicate that the transport of iodine and selenium to the fetus and infant is prioritized. Still, it is uncertain whether most infants had sufficient intakes. Further, the results might indicate an involvement of iodine in asthma development during the first year of life, which is essential to follow up. The low maternal and infant dietary intake of both iodine and selenium, especially when the mothers did not use supplements or iodized table salt, suggest a need for a general screening of women and young children.