Two trends in middle-class birth in the United States

This discussion focuses on two important trends in American childbirth that have emerged in the past 30 years, the demand for a perfect baby and the desire for a perfect birth. These two trends are particularly important in the subgroup of middle-class women who have decided on delayed childbearing. Tremendous technological innovations, such as ultra-sound, prenatal genetic analysis, and fetal monitoring, have promoted the perception that physicians can control the prenatal environment and predict the pregnancy outcome. This expectation may lead to bitterness and anger in the event of an adverse pregnancy outcome. In contrast, women and their families have also come to desire more control over the birth experience. If the parents’ birth plan is not achieved and their expectations not fulfilled, many parents feel they have not performed well. When the physician acts as a guide in the birth process, parents and physicians together may transcend the conflict to achieve a more satisfactory birth experience.     

A review of recent activity in the United States.

Either an overabundance or a deficiency of trace metals in the food chain can ultimately affect adversely the health of livestock and man. Increasing interest in the United States in the distribution of metals in the environment and in metal pollutants has led to widespread interdisciplinary research sponsored by governmental, private and academic groups concerning the availability of trace elements for absorption by plants and animals, and the effects of trace elements throughout the food chain. The state of the art and the needs for research are reviewed by interdisciplinary committees in the National Academy of Sciences and in many government agencies. Research is encouraged through contracts and grants awarded by federal and state agencies and the National Science Foundation to universities for studies of specific metals, specific diseases and correlations between metals and health in specific geographic areas. Effects on the environment of coal-fired power plants, the mining and processing of metals, asbestos, and phosphate, and the disposal of industrial and nuclear wastes have also received much attention in the past few years.     

Seasonality of first coitus in the United States.

Recent attention to causes of seasonality of births leads to an interest in seasonality patterns in the antecedents to birth, including gestational length, conception, and coital activity. In this paper we study the beginning of the process: first intercourse among adolescents and young adults. Analysis of a small and local dataset is suggestive that loss of virginity is particularly likely during the summer. A test of this "Summer Vacation Theory" using a large national dataset supports the generality of the phenomenon. Further, a prediction that seasonality patterns will change during the transition from high school to work and college is tested and supported. The existence of both biological and psycho-social mechanisms is suggested. Policy implications are reviewed.     

Environmental influences on the productivity of three desert succulents in the south-western United States

Abstract Net CO₂ uptake over 24 h periods for shoots of Agave deserti, Ferocactus acanthodes, and Opuntia ficus-indica was measured under the ranges of water status, air temperature, and photo-synthetically active radiation (PAR) that occur in the south-western U.S.A. An environmental productivity index (EPI) was constructed indicating the overall influence of these three factors on net CO₂ uptake. Using growth chambers whose conditions were changed monthly to simulate the environmental conditions at a field site, the observed shoot dry weight increases per unit surface area changed in concert with monthly changes in EPI. The observed dry weight gain of the shoot was 17–19% lower than the predicted shoot net CO₂ uptake, which could be accounted for by carbon diversion to the roots. Mean monthly EPI was also predicted for 21 sites in the south-western U.S.A. All three species had low EPIs in the Colorado River basin, which has low annual rainfall and high summer temperatures, and in the north-central part of the region, which has low temperatures and low PAR during winter when water is available. The two native species, A. deserti and F. acanthodes, had high EPIs beyond their range in coastal southern California, where competition by other vegetation for PAR may limit net CO₂ uptake. Such regions as well as south-central California and south-central Arizona had high EPIs for all three species, indicating that these areas would be appropriate for the cultivation of O. ficus-indica.     

Determinants of the sex ratio at birth: review of recent literature

The fact that more boys are born than girls (104-107 boys for every 100 girls) has been known since 1662. Factors determining the sex ratio at birth rate are of 2 kinds: factors determining the primary sex ratio, i.e., sex ratio at conception, and factors determining the survival of the embryo in utero. Y-bearing and X-bearing sperm may have different motility or different survival time. The age of the ovum at fertilization and the chemical balance of the female genital tract have an effect on sex ratio at conception. High levels of circulating gonadotropins may imply a lower sex ratio at birth as well as a higher rate of dizygotic twinning. Male conception also appears to be higher early and late in the menstrual cycle. The fact that women exposed to higher coital rates conceive earlier in the menstrual cycle may account for the greater number of boys born during wars. Prenatal male mortality is reportedly highest between gestational months 3-5, lower between months 6-8, and higher again st term. Also, immunological interaction between mother and embryo may account for some sex selective spontaneous abortions. 3 sociodemographic determinants of sex ratio at birth are thought to be maternal age, paternal age, and birth order. Higher prenatal male mortality may be correlated with socioeconomic conditions, since higher socioeconomic status lowers prenatal mortality in general. The effects of parental age, birth order, and parity are less clear. Race is also a factor, since the sex ratio at birth for blacks is lower (102-104) than for whites (106). 14 univariate and 19 multivariate studies of effects of maternal age, paternal age, parity, birth order, race, and socioeconomic status on sex ratio at birth, with sample sizes in the millions from various countries have been analyzed. More boys are born to younger parents, and lower order births have a higher proportion of males than do higher order births. In the multivariate analyses, when the effects of paternal and and birth order are controlled for, the effect of maternal age weakens, and the effect of paternal age appears to be stronger. The effect of birth order remains but is very small, and the effect of race persists independent of any effect of other variables. Maternal age, parity, and birth order are positively correlated with proportion of male stillbirths. The results of the multivariate analyses show all of the effects to be very small, but that maternal age has no effect on sex ratio at birth; paternal age and birth order have a negative effect, and the racial effect persists independent of any other effect. The racial effect is clearly biologically determined at conception because blacks have higher levels of circulating gonadotropin and therefore a higher probability of conceiving girls. Parents in higher socioeconomic classes are more likely to have sons, but the effect is largely due to the excess male mortality during most of the gestational period.     

Determinants of the sex ratio at birth: Review of recent literature

Abstract

Use of contraception by rural Egyptian women who desire no more children is examined within a modified microeconomic framework. Four sets of factors are hypothesized to influence current use of contraception: (1) costs of contraception, ‘(2) factors influencing the slope of the desired family size function, (3) anticipated costs of child rearing and (4) strength of motivation for fertility regulation. Women's education and two measures of psychic costs were found to be important predictors of contraceptive use. Factors affecting the demand for children and thus indirectly influencing the motivation for fertility regulation were also important. Land ownership, cultivating status of the household, and educational expectations for children were significantly related to current use. Strength of motivation, although significant, was less strongly related to use of contraception. The findings suggest women who want no more children, but who are not practicing contraception, are affected by factors influencing both the costs of contraception and the costs of an unwanted child.     

The influences of weather and topography on water bird migration in the southwestern United States

Summary Radar and visual observations were made on water bird migration throuh the Southwest at six stations from February 1973 through November 1974. The influence of weather on nocturnal non-passerine migration in the Southwest is less significant than reported for passerine migration elsewhere. Both seasonality and weather factors influence water bird migration, but the relative contribution of each is strongly dependent on the specific migration season. Spring migration, which has more extreme weather conditions, shows a stronger correlation to meteorological factors. Autumn migration in the Southwest rarely experiences severe weather, and consequently shows a stronger correlation to seasonality than to weather.The intensity of spring non-passerine migration was highly correlated with height of freezing level, temperature at sunset and midnight, humidity at sunset, cloud height at sunset and midnight, following winds aloft, and inversely related to change in temperature and day of the year. The most important variables listed by the stepwise linear multiple regression analysis were freezing level, following winds aloft, day of the year, and surface wind speed. When the height of the lowest cloud layer was allowed to enter the regression analysis, freezing level and cloud height were the most significant variables, with the intensity of migration higher with higher freezing level and higher cloud base. The most important variables predicting the occurrence or absence of migration were freezing level, barometric pressure and dew point.Autumn water bird migration was most highly correlated with cloud height and day of the year, and inversely correlated with humidity. The most important variables from the stepwise regression analysis and discriminant function analysis were day of the year, 670 m following-wind speed, and temperature. When cloud height was allowed to enter the model, it was the only significant factor influencing migration. As in spring, higher rates of autumn migration occurred with higher freezing levels.More migration occurred on the Great Plains than in the Rocky Mountains; but within the mountains, geography had little influence on the intensity of migration. Indirect evidence indicates that waterfowl and shorebirds move over the mountains (up to 2000 m above the surrounding terrain and 3500 m above sea level), rather than around them.     

Eugenist politics in the United States of America in the first xxth half-century

The United-States were the first country which had devised eugenist politics. The applications of theories had taken place as far as the end of the 1960's. They were placed one's reliance on two points: on the one hand, immigration's limitation and on the other hand an obligatory sterilisation of criminels and feebleminde people.