The use of oral contraceptive before pregnancy and breastfeeding duration: A cross-sectional study with retrospective ascertainment

<p>Abstract</p> <p>Background</p> <p>Various studies have identified risk factors associated with decreased breastfeeding duration. The aim of this study was to investigate whether there is an association between oral contraceptive (OC) use before pregnancy and breastfeeding duration.</p> <p>Methods</p> <p>In 1994/95, as part of a 3-year epidemiologic follow-up study of school children, reproductive interviews were conducted with their mothers. The study population consists of 663 women residing in Hesse, Central Germany; 575 provided information on their reproductive history. The interview included retrospective ascertainment of OC use, its timing before pregnancy, and duration of breastfeeding. To estimate its effect on duration of breastfeeding, survival analysis was applied controlling for maternal age, socio-demographic characteristics, smoking during pregnancy, age at menarche, planning of the pregnancy and birth order. Hazard ratios and median breastfeeding duration were estimated.</p> <p>Results</p> <p>The mean age of the women at delivery was 27.3 years. Among participants, 34.9% had high school education or less, 10.4% had more than 2 children, and 30.1% smoked during pregnancy. In total, oral contraceptive use in the 12 months before conception was reported by 40.4% of the women, within 3 months of conception by 18.4%. 81.4% (468/575) of women initiated breastfeeding. Compared to those who did not use OC in the 12 months preceding pregnancy, mothers who used OC during the 3 months before conception had a shorter duration of breastfeeding (HR = 1.29; 95% CI: 1.03, 1.61), as did mothers who stopped OC use 4–12 months before conception (HR = 1.27, 95% CI: 1.02, 1.58). Smoking during pregnancy and lower education were also significantly associated with shorter duration of breastfeeding.</p> <p>Conclusion</p> <p>The results suggest that OC use during the 12 months prior to conception may affect breastfeeding duration. These findings may be due to the endocrine disrupting effect of OC. Alternatively, both OC use and shorter duration of breastfeeding may represent lifestyle-related conditions.</p

Cautions of Using Allele-Based Tests Under Heterosis

Abstract: In genetic studies, heterotic effects are commonly assessed as dominant, additive, or recessive effects for a given genetic marker. However, the distorting effect of heterosis on statistical tests is non-trivial. An inheritance model needs to be carefully chosen to achieve highest testing power. We assess this through simulations via allele- and genotype-based tests. Chi-square test statistics for different inheritance models are formulated as a function of relative risks and allele frequencies. The results indicate that testing power from the commonly used allele-based tests can be substantially diminished by heterosis. Assessing the existence of heterosis is thus recommended to avoid false negative findings

Body Burden of Dichlorodiphenyl Dichloroethene (DDE) and Childhood Pulmonary Function

Longitudinal studies have shown that early life exposure to dichlorodiphenyl dichloroethene (DDE) can lead to growth reduction during childhood and adolescence. In addition, DDE exposure has been linked to respiratory tract infections and an increased risk of asthma in children. Our aim was to understand the relationships between DDE exposure and pulmonary function in children, and, particularly, whether associations are mediated by the height of the children. We used data from an environmental epidemiologic study conducted in central Germany in children aged 8-10 years. The pulmonary function (forced vital capacity, FVC, and forced expiratory volume in one second, FEV1) were measured in three consecutive years. Blood DDE levels were measured at 8 and 10 years. We used linear mixed models for repeated measurements and path analyses to assess the association between blood levels of DDE and pulmonary function measurements. All models were adjusted for confounders. Linear mixed approaches and modelling concurrent effects showed no significant associations. The path analytical models demonstrated that DDE measured at eight years had significant, inverse, indirect, and total effects on FVC at ten years (n = 328; −0.18 L per μg/L of DDE) and FEV1 (n = 328; −0.17 L per μg/L of DDE), mediated through effects of DDE on height and weight. The DDE burden reduces pulmonary function through its diminishing effects on height and weight in children. Further studies are required to test these associations in other samples, preferably from a region with ongoing, high DDT application

Sex Differences in the Association of Sibship Size and Position in Sibship with Lipid Profile During Adolescence: A Cross-Sectional Study

Background. Epidemiologic studies have reported associations of sibship size and position of the child in the sibship with multiple health outcomes, including adiposity and diabetes. However, little is known about sibling effects on lipids. Hence, this study sought to evaluate associations of the number of total, older, and younger siblings with lipid profile among adolescents. Methods. In a cross-sectional study among high school students aged 14 to 19 years, lipid levels were measured in capillary blood. Parents reported the number of siblings (total, older, and younger). Geometric means of lipids were calculated, and linear regression was used to estimate the ratio of geometric means (RoGM) and 95% confidence intervals (CI). Analyses were sex stratified. Results. Of the total study sample (n = 1,584), 758 (47.9%) were boys and 826 (52.1%) were girls, with median age of 16.0 years. Total cholesterol (TC) was lower by 8% (adjusted-RoGM = 0.92, 95% CI: 0.88–0.96) among boys with ≥3 older siblings compared to those with no older siblings. Similarly, boys with ≥3 younger sibling compared to those with no younger siblings had reduced TC by 7% (adjusted-RoGM = 0.93, 0.87–0.99). Moreover, an increased number of total siblings (≥4 vs. 0/1: adjusted-RoGM = 0.80, 0.67–97) and older siblings (≥3 vs. 0: adjusted-RoGM = 0.90, 0.82–0.98) were associated with reduced low-density lipoprotein cholesterol (LDL-C) among boys. Similarly, lower levels of triglycerides (TG) were seen among boys with ≥3 older siblings compared to those with no older siblings (adjusted-RoGM = 0.87, 0.78–0.96). A higher number of younger siblings was associated with increased high-density lipoprotein cholesterol (HDL-C) among boys (≥3 vs. 0: adjusted-RoGM = 1.08, 1.01–1.17). Sibship characteristics were not associated with lipids among girls. Conclusions. Increased number of total, older, and younger siblings were associated with favorable lipid profiles among adolescent boys, but not girls. Mechanisms underlying these associations need further investigations