1,720,976 research outputs found
Natural selection in industrialized countries: a study of three generations of Italian borns.
No full textWe have studied the impact of natural selection on the Italian population, analysing the relationship between stillbirth and three related variables: birth weight, birth order and maternal age. A progressive relaxation of selection with time has been demonstrated by the reduction of the Haldane index calculated with respect to the three variables
Heterogeneous effects of natural selection on the Italian newborns.
No full textWe have studied the impact of natural selection through stillbirth on the Italian population, taking into account the socio-economic heterogeneity of the country. The results suggest that older age at delivery and lower cultural level of the mothers, indicators of critical biological and socio-economic conditions, even at present increase stillbirth risk. Moreover, in the less favourable environment of the southern regions, selection is still sex-specific
Changes in twinning rate: Italy 1950-1996
No full textBACKGROUND: In the wide-ranging debate about the potential monitors of population fertility, twinning rate has been considered a candidate. In the developed countries, a decline in spontaneous twinning rate began around 1950 and continued until the late 1970s. The decrease in mean maternal age at delivery and the number of children per family have been considered as possible reasons for the decrease. The rise in twinning rates, which began in the 1980s, is probably due to the spread of assisted reproduction, at least for older mothers. METHODS: The temporal trend in twinning rate and the relationship with maternal age at delivery and birth order in the Italian population were analysed. RESULTS: The recent increase in twinning rate can be mainly attributed to the recourse to assisted reproduction techniques, as demonstrated by the twinning frequency among older primiparae. The twinning rate recently observed in young mothers approximates to the value of the 1950s, which is assumed to represent a 'natural' fertility condition. CONCLUSIONS: On the assumption that twinning is an indicator of fertility, and hence of population fitness, the present data seem to suggest that natural fertility has been slightly increasing in the Italian population
Sex ratio at reproductive age:changes over the last century in the Italian population.
No full textThe radical improvement in living conditions experienced in Italy during the last century caused a reduction in male extra-mortality during the prereproductive years. As a consequence, a progressive increase in the sex ratio at the beginning of the reproductive age (15-19 years) occurred, so that in recent times the sex ratio in the young adult population has approached the almost constant value of 1.06 observed at birth. We calculated that the sex composition would be the same in newborns and in young adults in about one generation: obviously, we have to assume that the sex differentials in mortality and migration are constant over time. The 1:1 equilibrium between sexes, which maximizes reproductive success, occurred in the 15-19 age group at the beginning of the century and shifted to the 30-35 age group in the 1990s. We compared the 1993-1995 sex ratios in different age groups in European Union countries and observed that in Italy as well as in other Mediterranean countries the numerical equality between sexes is reached at 30-35 years of age, while in north-central Europe it is reached later, approximately at the end of reproductive life
Early selection and sex composition in Italy: a study at regional level.
No full textWe have chosen four Italian regions with different degrees of industrialization and socioeconomic levels to study environmental differences in the sex ratio. The improvement in living and sanitary conditions during the last century has led to a progressive reduction in early male extramortality, and the sex ratio at birth has been almost unchanged at least to the first year of life and probably up to reproductive age. To investigate whether socioeconomic, cultural, or biological factors still influence the sex ratio at birth, we studied the stillbirth rate and the relations between newborn viability and sex composition as a function of maternal age and educational level. Our results suggest that in less favorable environments early selection against male newborns is almost twice that against female newborns when the mothers are the least favored for socioeconomic status, cultural level, and biological conditions (older than 39 years)
Trends in childbearing and stilbirth risk: heterogeneity among Italian regions.
No full textIn Italy, as in all Western countries, the almost monotonic decline in fertility observed since the 1960s has been paralleled until the beginning of the 1980s by a decrease in maternal age at delivery. Since then, age at marriage and at childbearing has been increasing and marital fertility has continued to decrease. By 1994 Italy showed extreme values of low total fertility rate (1.22) and of high mean maternal age at delivery (29.7). For the period between 1960 and 1994 we identified five U-shaped patterns in maternal age at delivery corresponding to five geographical areas, which differ socioeconomically and culturally. Since it is well known that an increase in the maternal age is accompanied by an increase in the risk of unfavorable pregnancy outcome, we estimated the stillbirth risk run by older (> or =35 years) mothers who delivered in 1994, with respect to their younger counterparts. The differences between the areas are reflected in the higher risk in southern compared to northern Italy: the maximum value occurred in Sicily (odds ratio 2.02, 95% confidence interval, 1.51-2.70) and the minimum value, even lower than in the north but not statistically significant, was found in Sardinia (odds ratio 1.25, 95% confidence interval, 0.81-1.91), known to be characterized by peculiar cultural and biological features
Natural selection and reproductive behavior.
No full textWe studied the relaxation of natural selection affecting the newborn population in Italy between 1930 and 1993 due to the decrease in the stillbirth (mortality) rate and the simultaneous changes in women's reproductive behavior (strategies). Results show that, apart from a drastic overall reduction, the stillbirth rate has varied among different groups of neonates. The present stillbirth rate of less than 5 per thousand, observed in 8 of the 20 phenotypic classes defined on the basis of maternal age at delivery and neonate birth order, most likely represents an unavoidable biological or genetic cost. A 9 per thousand stillbirth rate, about twice the potential minimum, exists among neonates born to women delivering at advanced age (> or = 35): the risk they face at the first or, in adverse living conditions, the fourth pregnancy could, however, be decreased by a policy aimed at countering the tendency to delay maternity and improving antenatal care in economically disadvantaged areas of the country
An electrophoretic polymorphism that mimics a true genetic polymorphism in Triturus cristatus carnifex (Amiphibia, Urodela).
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