Seasonality of conception in human populations in Chile

Seasonality of conceptions in human populations in Chile was studied for a period of 30 years (1945–1974). Clear seasonal conception courses exist in the country, exception made of the northern and southern extremes. Seasonal flux is concentrated mainly in January, but also secondary increases in April and June were observed. Along the 30-year period a general pattern of decreasing seasonality is observed. Conception is significantly related to temperature and photoperiod in this country, the maximum rates of conceptions being observed in coincidence with the maximum temperatures and photoperiods. Nonclimatic factors which may be affecting seasonality of conceptions are also discussed.     

Seasonality of birth in nineteenth- and twentieth-century Austria

We present an analysis of birth seasonality in nine geographical regions within Austria for two time periods, 1881-1912 and 1947-1959. In the early period, geography, climate, and agricultural patterns were related to birth seasonality. By the latter time period, these factors were no longer related to birth seasonality. We propose a "resilience hypothesis," which suggests two levels of causal influences on birth seasonality. First, underlying the three significant features of birth seasonality patterns around the world are only a small number of major causes. But, second, there are a multiplicity of minor causes that result in small perturbations in these otherwise resilient and consistent patterns.     

Seasonality of birth and sex ratio in Tehran, Iran

234 218 births (1975-1983) from a hospital in Tehran have been analysed for seasonality of birth and sex ratio. The results show more births in winter and less births in fall. The sex ratio is higher in summer and lower in fall. The occurrence of multibirths shows higher twinning and triplet rates in spring and fall, respectively, whereas lower twinning and triplet rates occur in winter and summer, respectively. It could be demonstrated that geographical factors influence the rates of births and multibirths as well as the sex ratio.     

Seasonality of macroalgae and epilithic diatoms in spring-fed streams in Texas, USA

A seasonal study of two spring-fed stream systems in south-central Texas was undertaken over a 15-month period from June 1996 to September 1997. Relative abundance of the epilithic diatom flora, percent cover of macroalgae, and several physical and chemical conditions were monitored in one 20-m stretch in each of the streams at approximately two-month intervals. Six additional spring-fed stream segments were sampled in May 1996 for macroalgae and measured for the same conditions, in order to determine how representative the macroalgal floras of the study sites were of south-central and western Texas. Conditions in the two stream segments were relatively constant over the 15 months, except for maximum depth; this finding is similar those reported for other spring-fed systems worldwide. Sixty-eight diatom taxa and nine macroalgae taxa were identified from the San Marcos River, which compares to 46 diatom taxa and six macroalgae taxa from the Comal River. Several diatom and macroalgae species were significantly correlated to stream conditions (e.g. Dichotomosiphon tuberosus and Hildenbrandia angolensis with daylength, and Amphora pediculus with maximum depth). Twenty-one macroalgal taxa were identified from the six additional spring-fed steam segments. Conditions in these streams were very similar to those measured in the San Marcos River and Comal River, except that they had a higher average pH _x= 8.1 versus _x= 7.6). The epilithic diatom flora of the San Marcos River and the Comal River contains many of the diatom and some macroalgal taxa commonly reported from springs globally. This revised version was published online in July 2006 with corrections to the Cover Date.     

Annual pattern of human conception in the State of Texas

A total of 2,828,068 State of Texas singleton conceptions, estimated from the date of the first day of the last menstrual period, were assessed for annual periodicity by multiple-component (1-yr fundamental plus the 6- and 3-month harmonics) Cosinor analysis. An annual pattern (p < 0.001) of conception was detected with a December peak, end of July-beginning of August trough and modest amplitude (total peak-to-trough variation) equal to 13.3% of the yearly mean. Annual patterns (p < 0.005) of generally comparable peak and trough times were also documented for conceptions categorized by maternal marital status, age, ethnicity, years of education, birthplace, and county (Texas-Mexico border vs. non-border) of residence. The amplitude, a measure of the prominence of the annual pattern, varied by race (two-fold greater for non-Hispanic Blacks and Hispanics than non-Hispanic Whites), age (50-60% greater for the 19-year-old and younger group than the 20-29 and 30-44-year-old groups) and maternal education (two-fold greater for those with 0-8 than 13 or more years of schooling). Annual patterns (p < 0.001) in conceptions, generally with December peak and end of July-beginning of August trough, were also detected for neonatal variables categorized by birth weight, birth order, gestational age, and gender. The amplitude of the annual pattern in conceptions varied directly with gestational age and inversely with birth weight class.     

Seasonality of birth in the majors, 1880-1999

We examined two alternative explanations, one demographic, the other sociological, for the uneven distribution of birth months of Major League baseball (MLB) players active between 1880 and 1999. Beginning in 1900, players born between August and October were significantly overrepresented, and this uneven distribution was almost identical for the next five 20-year periods. During the last 20-year period (1980-1999), the disparity in birth months became even more pronounced. Ethnicity, handedness, player position, accomplishment (winning an award), and career length were not significantly related to birth month. Prior to 1980, the distribution of births for MLB players did not differ significantly from the distribution for the general population, but after 1980, it did. We concluded that up until 1980, the uneven distribution of birth months in MLB originated in the demographic seasonality-related excess number of births in August and September in the United States. Beginning in the 1980s, this seasonality pattern was institutionally reinforced by the growing influence of Little League and related junior baseball leagues and their reliance on the August 1 birth date for age grouping.     

Maternal residential proximity to nuclear facilities and low birth weight in offspring in Texas

Health effects of close residential proximity to nuclear facilities have been a concern for both the general public and health professionals. Here, a study is reported examining the association between maternal residential proximity to nuclear facilities and low birth weight (LBW) in offspring using data from 1996 through 2008 in Texas, USA. A case–control study design was used together with a proximity-based model for exposure assessment. First, the LBW case/control births were categorized into multiple proximity groups based on distances between their maternal residences and nuclear facilities. Then, a binary logistic regression model was used to examine the association between maternal residential proximity to nuclear facilities and low birth weight in offspring. The odds ratios were adjusted for birth year, public health region of maternal residence, child’s sex, gestational weeks, maternal age, education, and race/ethnicity. In addition, sensitivity analyses were conducted for the model. Compared with the reference group (more than 50 km from a nuclear facility), the exposed groups did not show a statistically significant increase in LBW risk [adjusted odds ratio (aOR) 0.91 (95% confidence interval (CI): 0.81, 1.03) for group 40–50 km; aOR 0.98 (CI 0.84, 1.13) for group 30–40 km; aOR 0.95 (CI 0.79, 1.15) for group 20–30 km; aOR 0.86 (CI 0.70, 1.04) for group 10–20 km; and aOR 0.98 (CI 0.59, 1.61) for group 0–10 km]. These results were also confirmed by results of the sensitivity analyses. The results suggest that maternal residential proximity to nuclear facilities is not a significant factor for LBW in offspring.     

Seasonality of birth: Two findings from the decennial census

Abstract

Two results on the seasonality of birth phenomenon are derived from tabulations of 1980 census data: first, that the familiar pattern of spring trough and summer peak prevailed in the decades before the establishment of a national birth registration data system; second, that the seasonal pattern is most pronounced for the lower socioeconomic group.     

Seasonality of birth: two findings from the decennial census

The enigmatic seasonality of births in the US has been analyzed extensively, but gaps in the knowledge of this phenomenon exist along dimensions not accessed by the national vital registration system. Live births in the US have for some time followed a pattern of spring trough and summer peak--at least since the initiation of the national birth registration system in 1933. The pattern is known to be more pronounced for the South than for other regions and for blacks than for whites. In this study it has been shown that this pattern existed as far back as the 1890's, and currently is more pronounced for lower than for higher socioeconomic groups. These findings come from an analysis of census population data, rather than vital registration data. In this way census data have been used in an innovative way to address 2 aspects of the phenomenon which had heretofore not been adequately treated.     

Seasonality in the incidence of cervical carcinoma in teenagers and young adults in Northern England, 1968-2005

Infection with human papillomavirus is an established risk factor for cervical carcinoma. However, the role of other environmental factors is less well established. To further investigate whether other agents may be involved, the authors have analyzed seasonal variation in cervical cancer with respect to month of birth and separately month of diagnosis. All 85 cases diagnosed in 15-24-yr-olds during the period 1968-2005 were extracted from the specialist population-based Northern Region Young Persons' Malignant Disease Registry. The chi-square heterogeneity test was used to assess overall nonuniform variation in month of birth and separately month of diagnosis. Poisson regression analysis was used to fit sinusoidal (harmonic) models to the data using month of birth and month of diagnosis in separate models. Based on month of birth, there was statistically significant heterogeneity (p=.03) and a significant sinusoidal pattern, with an incidence peak involving births in the autumn months (p=.03). Based on month of diagnosis, there was marginally significant heterogeneity (p=.06). The evidence of seasonal variation around time of birth for cervical carcinoma is highly novel and suggests possible early etiological involvement of environmental factors.