Showing papers on "Fertility published in 2002"

The Emergence of Lowest‐Low Fertility in Europe During the 1990s

Abstract: Lowest-low fertility, defined as a period total fertility rate at or below 1.3, has rapidly spread in Europe during the 1990s. This article traces the emergence of this new phenomenon to the interaction of five factors. First, tempo and compositional distortions reduce the total fertility rate below the associated level of cohort fertility. Second, socioeconomic changes—including increased returns to human capital and high economic uncertainty in early adulthood—have made late childbearing a rational response for individuals and couples. Third, social interaction effects reinforce this behavioral adjustment and contribute to large and persistent postponement in the mean age at birth. Fourth, institutional settings favor an overall low quantum of fertility. Fifth, postponement–quantum interactions amplify the consequences of this institutional setting when combined with ongoing delays of child-bearing. The article concludes with speculations about future trends in current and prospective lowest-low-fertility countries.

The variability of female reproductive ageing

Abstract: The delay in childbearing is an important societal change contributing to an increasing incidence of subfertility. The prevailing concept of female reproductive ageing assumes that the decline of both quantity and quality of the oocyte/follicle pool determines an age-dependent loss of female fertility. There is an apparent discrepancy between the ability to maintain a regular ovulatory cycle pattern and the several years earlier cessation of female fertility. This latter is largely explained by an age-related increase of meiotic non-disjunction leading to chromosomal aneuploidy and early pregnancy loss, such that most embryos from women > or =40 years old are chromosomally abnormal and rarely develop further. The final stage of reproductive ageing-the occurrence of menopause-shows a huge variation between women. Age at last birth in natural fertility populations, which marks the end of female fertility, shows an identically wide variation as age at menopause, but occurs on average 10 years earlier. Given the high heritability for age at menopause, the variation in both age of menopause and last birth are probably under genetic control by the same set of genes. Some of those genes must carry heritable variants which modulate the rate of ovarian ageing and give rise to the wide age variations for the various phases of reproductive ageing.

Genetic dissection of mammalian fertility pathways.

Abstract: The world's population is increasing at an alarming rate and is projected to reach nine billion by 2050. Despite this, 15% of couples world-wide remain childless because of infertility. Few genetic causes of infertility have been identified in humans; nevertheless, genetic aetiologies are thought to underlie many cases of idiopathic infertility. Mouse models with reproductive defects as a major phenotype are being rapidly created and discovered and now total over 200. These models are helping to define mechanisms of reproductive function, as well as identify potential new contraceptive targets and genes involved in the pathophysiology of reproductive disorders. With this new information, men and women will continue to be confronted with difficult decisions on whether or not to use state-of-the-art technology and hormonal treatments to propagate their germline, despite the risks of transmitting mutant genes to their offspring.

Inequality and Growth: Why Differential Fertility Matters

Abstract: We develop a new theoretical link between inequality and growth. In our model, fertility and education decisions are interdependent. Poor parents decide to have many children and invest little in education. A mean-preserving spread in the income distribution increases the fertility differential between the rich and the poor, which implies thatmore weight gets placed on families who provide little education. Consequently, an increase in inequality lowers average education and, therefore, growth. We find that this fertility-differential effect accounts for most of the empirical relationship between inequality and growth.

A note on the changing relationship between fertility and female employment rates in developed countries

Abstract: In this paper we look at a panel of OECD aggregate fertility and labor market data between 1970 and 1995 and we report some striking recent developments Total Fertility Rates (TFR) were falling and Female Participation Rates (FPR) were increasing, conforming to a well known long-run trend Along the cross-sectional dimension, the correlation between TFR and FPR was negative and significant during the 1970's and up to the early 1980's This seemed consistent with secular comovements However, by the late 1980's the correlation had become positive and equally significant We discuss our findings within the framework of standard neoclassical models of fertility and labor supply adapted to macro data, as in Butz and Ward (1979)

Births: final data for 2000.

Abstract: Objectives—This report presents 2000 data on U.S. births according to a wide variety of characteristics. Data are presented for maternal demographic characteristics including age, live-birth order, race, Hispanic origin, marital status, and educational attainment; maternal characteristics (medical risk factors, weight gain, tobacco and alcohol use); medical care utilization by pregnant women (prenatal care, obstetric procedures, complications of labor and/or delivery, attendant at birth, and method of delivery); and infant characteristics (period of gestation, birthweight, Apgar score, abnormal conditions, congenital anomalies, and multiple births). Also presented are birth and fertility rates by age, live-birth order, race, Hispanic origin, and marital status. Selected data by mother’s State of residence are shown, as well as data on month and day of birth, sex ratio, and age of father. Trends in fertility patterns and maternal and infant characteristics are described and interpreted. Methods—Descriptive tabulations of data reported on the birth certificates of the 4.059 million births that occurred in 2000 are presented. Results—The number of births rose 3 percent in 2000; birth and fertility rates rose 1 to 2 percent. The total fertility rate was above ‘‘replacement’’ for the first time in almost 30 years. Teenage birth rates continued to fall while birth rates for women aged 20–24 years rose slightly, and rates for women in their late twenties and thirties rose 3 to 5 percent. Births to women in their forties and early fifties were also up for 2000. The number of births to unmarried women, the birth rate, and the percent of births that were to unmarried women rose 1 to 3 percent, but birth rates for unmarried teenagers declined. Smoking by pregnant women was down again. The cesarean delivery rate rose 4 percent to 22.9, the fourth consecutive increase; the primary cesarean rate was up and the rate of vaginal births after a previous cesarean was down. The number and rate of twin births continued to rise, but the triplet/+ birth rate declined for the second year in a row. For the first year in almost a decade the preterm birth rate declined (to 11.6 percent); the low birthweight rate, however, was unchanged at 7.6 percent.

Changes with age in the level and duration of fertility in the menstrual cycle

Abstract: BACKGROUND: Most analyses of age-related changes in fertility cannot separate effects due to reduced frequency of sexual intercourse from effects directly related to ageing. Information on intercourse collected daily through each menstrual cycle provides the data for estimating day-specific probabilities of pregnancy for specific days relative to ovulation, and these estimates allow unconfounded analysis of ageing effects. METHODS: A total of 782 healthy couples using natural family planning methods contributed prospective data on 5860 menstrual cycles. Day of ovulation was based on basal body temperature measurements. Estimates of day-specific probabilities of pregnancy and the length of the fertile window were compared across age groups. RESULTS: Nearly all pregnancies occurred within a 6 day fertile window. There was no evidence for a shorter fertile window in older men or women. On average, the day-specific probabilities of pregnancy declined with age for women from the late 20s onward, with probabilities of pregnancy twice as high for women aged 19–26 years compared with women aged 35–39 years. Controlling for age of the woman, fertility was significantly reduced for men aged >35 years. CONCLUSIONS: Women’s fertility begins to decline in the late 20s with substantial decreases by the late 30s. Fertility for men is less affected by age, but shows significant decline by the late 30s.

The Effect of Child Care and Part Time Opportunities on Participation and Fertility Decisions in Italy

Abstract: Economic models of household behavior typically yield the prediction that increases in schooling levels and wage rates of married women lead to increases in their labor supply and reductions in fertility. In Italy, as well as in other Southern European countries, low labor market participation rates of married women are observed together with low birth rates. Our proposed explanation for this apparent anomaly involves the Italian institutional structure, particularly as reflected in rigidities and imperfections in the labor market and characteristics of the publicly-funded child care system. These rigidities tend to simultaneously increase the costs of having children and to discourage the labor market participation of married women. We analyze a model of labor supply and fertility, using panel data from the Bank of Italy which have been merged with regional data describing the available opportunities in each sample household's environment. The empirical results show that the availability of child care and part time work increase both the probability of working and having a child. Policies which would provide more flexible working hours choices and greater child care availability would aid in reducing the financial burden of children.

The effect of child care and part time opportunities on participation and fertility decisions in Italy

Abstract: Economic models of household behavior typically yield the prediction that increases in schooling levels and wage rates of married women lead to increases in their labor supply and reductions in fertility. In Italy, low labor market participation rates of married women are observed together with low birth rates. Our explanation involves the Italian institutional structure, particularly as reflected in rigidities and imperfections in the labor market and characteristics of the publicly-funded child care system. These rigidities tend to simultaneously increase the costs of having children and to discourage the labor market participation of married women. We analyze a model of labor supply and fertility, using panel data. The empirical results show that the availability of child care and part time work increase both the probability of working and having a child.

Infertility, Fertility Drugs, and Ovarian Cancer: A Pooled Analysis of Case-Control Studies

Abstract: Controversy surrounds the relations among infertility, fertility drug use, and the risk of ovarian cancer. The authors pooled interview data on infertility and fertility drug use from eight case-control studies conducted between 1989 and 1999 in the United States, Denmark, Canada, and Australia. Odds ratios and 95% confidence intervals were calculated, adjusting for age, race, family history of ovarian cancer, duration of oral contraception use, tubal ligation, gravidity, education, and site. Included in the analysis were 5,207 cases and 7,705 controls. Among nulligravid women, attempts for more than 5 years to become pregnant compared with attempts for less than 1 year increased the risk of ovarian cancer 2.67-fold (95% confidence interval (CI): 1.91, 3.74). Among nulliparous, subfertile women, neither any fertility drug use (odds ratio (OR) = 1.60, 95% CI: 0.90, 2.87) nor more than 12 months of use (OR = 1.54, 95% CI: 0.45, 5.27) was associated with ovarian cancer. Fertility drug use in nulligravid women was associated with borderline serous tumors (OR = 2.43, 95% CI: 1.01, 5.88) but not with any invasive histologic subtypes. Endometriosis (OR = 1.73, 95% CI: 1.10, 2.71) and unknown cause of infertility (OR = 1.19, 95% CI: 1.00, 1.40) increased cancer risk. These data suggest a role for specific biologic causes of infertility, but not for fertility drugs in overall risk for ovarian cancer.

The End of the Fertility Transition in the Developed World

Abstract: By the late 1990s the average period total fertility rate in the developed world had declined to 16, a level substantially lower than projected in the 1970s and 1980s This article examines recent trends and patterns in fertility in the developed world with particular emphasis on the effects and implications of changes in the timing of childbearing The main objective is to demonstrate that while fertility in these countries is indeed low, women's childbearing levels are not as low as period measures such as the total fertility rate suggest To obtain a full understanding of the various dimensions of fertility change several indicators are examined, including period and cohort fertility by birth order and childbearing preferences An analysis of these indicators demonstrates that period fertility measures in many developed countries are temporarily depressed by a rise in the mean age at childbearing The distortion of the TFR is as great as 04 births per woman in Italy and Spain These effects have been present in many developed countries since the 1970s and could continue for years into the future But tempo effects are temporary, and once the postponement of childbearing ends—as it eventually must—the corresponding fertility-depressing effect stops, thus putting upward pressure on period fertility Countries with very low fertility and substantial tempo effects may well experience rises in fertility in the near future if the timing of childbearing stabilizes Even if this happens, however, it seems unlikely that fertility will rebound to the replacement level

Births: final data for 2001.

Abstract: Objectives This report presents 2001 data on U.S. births according to a wide variety of characteristics. Data are presented for maternal demographic characteristics including age, live-birth order, race, Hispanic origin, marital status, and educational attainment; maternal characteristics (medical risk factors, weight gain, tobacco, and alcohol use); medical care utilization by pregnant women (prenatal care, obstetric procedures, complications of labor and/or delivery, attendant at birth, and method of delivery); and infant characteristics (period of gestation, birthweight, Apgar score, abnormal conditions, congenital anomalies, and multiple births). Also presented are birth and fertility rates by age, live-birth order, race, Hispanic origin, and marital status. Selected data by mother's State of residence are shown, as well as data on month and day of birth, sex ratio, and age of father. Trends in fertility patterns and maternal and infant characteristics are described and interpreted. Methods Descriptive tabulations of data reported on the birth certificates of the 4.026 million births that occurred in 2001 are presented. Denominators for population-based rates are derived from the 1990 U.S. census. As a result, rates are generally larger than would be the case if 2000-based estimates were used. The magnitude of the overestimate will vary by population subgroup; overestimates are likely greatest for those of Hispanic origin. Results The number of births, the birth rate, fertility rate, and total fertility rates all declined 1 percent in 2001. The teenage birth rate reached another historic low. Birth rates for women in their twenties declined slightly, whereas rates for women aged 30 to 44 years continued to rise. Births to unmarried women changed very little. Smoking by pregnant women was down again. Women were more likely to begin care in the first trimester of pregnancy (83.4 percent). The cesarean delivery rate rose for the fifth consecutive year to 24.4 percent; the primary cesarean rate was up 5 percent and the rate of vaginal births after a previous cesarean fell 20 percent. Preterm and low birthweight levels both rose for 2001. The twin birth rate continued to climb, and following 2 years of decline, the rate of triplet/+ births also increased.

What are the implications of myomas on fertility? A need for a debate?

Abstract: In order to evaluate the relationship between leiomyomas and infertility, which remains a subject of debate, we have tried to evaluate the impact of myomas on fertility and pregnancy outcome in different conditions where myomas are implicated. Medline research was conducted of publications appearing between January 1988 and August 2001 on the subjects of myomas and myomectomy and their impact on fertility and pregnancy outcome in infertile women. A total of 106 manuscripts were consulted. The incidence of myomas in infertile women without any obvious cause of infertility is estimated to be 1-2.4%. The relationship between leiomyomas and infertility remains a subject of debate. The question is: do myomas influence fertility? We are obliged to conclude that the question remains. The absence of an answer to this crucial question is probably due to the fact that we have not yet conducted the appropriate prospective studies required to obtain any clear results.

East–West gradient in semen quality in the Nordic–Baltic area: a study of men from the general population in Denmark, Norway, Estonia and Finland

Abstract: BACKGROUND Denmark and Norway have a three-fold higher incidence of testicular cancer than Estonia and Finland. Groups of young men from Denmark, Norway, Finland and Estonia were investigated to elucidate whether semen parameters and other related parameters follow a gradient between these countries, as does the gradient in incidence of testicular cancer. METHODS In total, 968 young men from the general population in these four countries were investigated according to the same protocol. Possible confounders were evaluated, and included in the statistical analysis when appropriate. Inter-laboratory differences in assessment of sperm concentrations were controlled by an external quality control programme and morphology assessment was centralized to one person. RESULTS The Finnish and Estonian men had an adjusted median sperm concentration of 54 and 57 x 10(6)/ml, respectively and the Norwegian and Danish men 41 x 10(6)/ml. The corresponding total sperm counts were 185, 174, 133 and 144 x 10(6). The frequency of normal sperm in men from Finland was 8.9%, Estonia 9.2%, Norway 6.9% and Denmark 6.4%. Within all four groups of men, a relationship between increasing levels of inhibin-B and increasing sperm counts was observed. However, inhibin-B levels were not predictive of sperm count differences between countries. CONCLUSIONS It is believed that the men examined were representative of the normal population of young men in all four countries as they were recruited from groups attending a compulsory medical examination, and not selected for known fertility or semen quality. Moreover, the majority of participants had no prior knowledge of their fertility potential. It appears that an east-west gradient exists in the Nordic-Baltic area with regard to semen parameters, this being in parallel with the incidences of testicular cancer. Further investigations are required to determine whether these findings are due to genetic differences, to different environments, or perhaps to a combination of both factors.

Time to pregnancy and semen parameters: a cross-sectional study among fertile couples from four European cities

Abstract: BACKGROUND: In fertile populations, little is known about the association between semen parameters and time to pregnancy (TTP) METHODS: Pregnant women from Copenhagen, Edinburgh, Paris and Turku who conceived without medical intervention were asked for their TTP (942 couples), and their partners provided a semen sample The proportion of morphologically normal sperm and the multiple anomalies index (MAI, ratio of the total number of anomalies to the number of abnormal sperm) were centrally estimated We estimated rate ratios for the occurrence of a pregnancy by a discrete survival model, adjusted for sexual activity and female factors affecting fecundity RESULTS: Increasing sperm concentration influenced TTP up to 5510 6 /ml The proportion of morphologically normal sperm influenced TTP up to 39% according to David’s criteria, and this association held among the subjects with a sperm concentration >5510 6 /ml For strict criteria, the threshold value was 19% normal sperm An increase of 05 in MAI was associated with an adjusted rate ratio for the occurrence of a pregnancy of 068 (95% confidence interval: 054–085) CONCLUSIONS: These results highlight the importance of sperm morphology parameters and indicate that the effect of proportion of normal sperm on TTP may be independent of sperm concentration

Education and fertility in sub-Saharan Africa: individual and community effects.

Abstract: Using data from Demographic and Health Surveys for 22 countries in sub-Saharan Africa, I show that the average educational level in a village or a community of a similar size has a significant depressing effect on a woman’s birth rates, net of urbanization and her own education. According to simulations, average fertility for these countries would be 1.00 lower if education were expanded from the current level in the region to the relatively high level in Kenya. The exclusion of aggregate education from the model leaves a response of only 0.52. A considerable aggregate contribution is estimated even when several potential determinants of education are included. This finding illustrates the need to consider aggregate education in future assessments of the total impact of education.

Child Labour, Fertility, and Economic Growth*

Abstract: This paper explores the evolution of child labour, fertility and human capital in the process of development. In early stages of development, the economy is in a development trap where child labour is abundant, fertility is high and output per capita is low. Technological progress, however, gradually increases the wage differential between parental and child labour, thereby inducing parents to substitute child education for child labour and reduce fertility. The economy takes off to a sustained growth steady-state equilibrium where child labour is abolished and fertility is low. Prohibition of child labour expedites the transition process and generates a Pareto dominating outcome.

On the Changing Correlation Between Fertility and Female Employment over Space and Time

Abstract: Various authors find that in OECD countries the cross-country correlation between the total fertility rate and the female labour force participation rate turned from a negative value before the 1980s to a positive value thereafter. Based on pooled cross-sectional data, Kogel (2004) shows that (a) unmeasured country-specific factors and (b) country-heterogeneity in the magnitude of the negative time-series association accounts for the reversal in the sign of the cross-country correlation coefficient. Our paper aims to identify those variables that may explain country heterogeneity in the negative association between fertility and female labour force participation. The selection of variables is based on existing macro-demographic theories. We apply aggregate descriptive representations of the time series and cross-country evolution of fertility, female employment and a set of labour market,educational and demographic variables and indicators of social policy.

Muslim and Non-Muslim Differences in Female Autonomy and Fertility: Evidence from Four Asian Countries

Abstract: The hypothesis that greater female power and autonomy produce lower fertility appears in many explanations of fertility differences and change (Dyson and Moore 1983; Cain Khanam and Nahar 1979; Basu 1992; Jeejeeboy 1995). This article examines the specific claim that the higher fertility of Muslims (compared to non-Muslims) can be traced to the lower level of power and autonomy (hereafter autonomy) afforded Muslim women. This lower autonomy reflects more rigid forms of patriarchy that characterize Muslim communities. Key elements of this argument "in here at the systemic institutional aggregate level" and thus require analysis at the community level (Smith 1989: 173-174; see also Balk 1994; Jeejeeboy and Sathar 2001). From a set of surveys of more than 50 communities in four Asian countries we identify 14 Muslim/non-Muslim pairwise community comparisons--that is pairs of communities that share many characteristics but differ in that one is predominately Muslim and the other predominately non-Muslim. Although not representative of any country or region these pairs of communities reflect substantial diversity of social and economic setting. Across most pairs of settings we show that Muslims have more children are more likely to want another child and if they want no more children are consistently less likely to be using contraception. We test whether these differences parallel differences in married womens autonomy. We use data collected for the purpose of investigating womens power autonomy and fertility: the Survey on the Status of Women and Fertility (SWAF). These data collected in 1993 and 1994 include a number of potentially relevant dimensions of womens autonomy: freedom of movement economic autonomy and exposure to intimidation/coercion. Direct measurement of multiple dimensions of autonomy avoids many of the criticisms of prior research on "womens status" and fertility (as discussed in Mason 1984 1996 1987). (excerpt)

The Idea of a Second Demographic Transition in Industrialized Countries

Abstract: 1. The basic idea At the end of the 19 th century several French scholars noted that a remarkable change was taking place in the population of their country. The number of children per family declined, clearly as the result of deliberate efforts to reduce fertility within marriage. It was soon understood that the voluntary limitation of marital fertility was a revolutionary novelty and the term 'demographic revolution' was, in fact, the original term used to describe it. Efforts to explain what was happening began almost immediately. Interestingly enough these first explanations assumed the phenomenon reflected what people wanted out of life. Dumont (1890:130) argued that the desire to be upwardly mobile was the root cause. When climbing the social ladder having a large family would be, no doubt, a hindrance. Dumont concluded that, as a result, the birth rate would decline as social mobility increased. Other French authors, such as Leroy-Beaulieu (1896) and Landry (1909) attributed it to changes in the moral order. Towards the end of the Second World War, and also after it, American scholars took de lead in the discussions about the demographic changes that were taking place. As a result the explanations preferred became more economic in nature and the term 'transition' replaced the term revolution. The changes in demographic behaviour were considered to be mainly a function of progress in society (Kirk, 1944:28). Notestein (1945), who played a crucial part in the formulation of the demographic transition theory, stressed the overriding importance of mortality decline and the impact of the modernization process in people's lives and in society as a whole. He concluded that the demographic transition was likely to be a universal phenomenon; all countries were bound to pass through it once they had achieved the level of development required. It was understood by all knowledgeable people that the decline in fertility was an adjustment made necessary by the decline in mortality. The latter had resulted in unsustainably high levels of natural population growth. The long-term demographic balance had been upset; consequently a new balance had to be established at low levels of both mortality and fertility. The very appealing assumption was that we would move from one long-term quasi- equilibrium to another. As Bongaarts recently stated in a paper (2001:260): 'If fertility in contemporary post-transitional societies had indeed levelled off at or near the replacement level, there would have been limited interest in the subject because this would have been expected.' He then continues as follows: 'However, fertility has dropped below the replacement level -sometimes by a substantial margin- in virtually every population that has moved through the demographic transition. If future fertility remains at these low levels, population will decline in size and age rapidly.' The basic idea behind the concept of the Second Demographic Transition as launched in 1986 is that industrialized countries have indeed reached a new stage in their demographic

Nonmarital childbearing: influences of education, marriage, and fertility.

Abstract: We examined the determinants of nonmarital fertility, focusing on the effects of other life-course events: education, marriage, marital dissolution, and marital fertility. Since these determinants are potentially endogenous, we modeled the processes that generate them jointly with nonmarital fertility and accounted for the sequencing of events and the unobserved correlations across processes. The results showed that the risk of nonmarital conception increases immediately after leaving school and that the educational effects are less pronounced for black women than for other women. The risk is lower for previously married women than for never-married women, even controlling for age, but this reduction is significant only for black women. The more children a woman already has, the lower her risk of nonmarital childbearing, particularly if the earlier children were born during a previous marriage. Ignoring endogeneity issues seriously biases the estimates of several substantively important effects.

Monitoring Contraceptive Continuation: Links to Fertility Outcomes and Quality of Care

Abstract: This study examines the fertility consequences of contraceptive discontinuation, describes cross-national variation in continuation rates, and assesses the usefulness of the contraceptive discontinuation rate as a summary outcome indicator of quality of care. In the 15 countries included in this analysis, the total fertility rate would be between 28 and 64 percent lower if the births following discontinuations that were not the result of a desire to become pregnant had not occurred. The all-method discontinuation rate for quality-related reasons emerges as the most likely candidate for a summary measure of quality of care. Within a year of starting use of a method, between 7 and 27 percent of women cease to practice contraception for reasons related to the quality of the service environment. The results imply that as fertility declines, family planning programs would profit from a shift in emphasis from providing methods to new clients toward providing services to reduce discontinuation rates.

Fertility after ileal pouch-anal anastomosis in women with ulcerative colitis.

Abstract: Background: Women with ulcerative colitis are believed to have normal fertility but colectomy and ileal pouch–anal anastomosis (IPAA) may impair fertility. The aim was to compare fertility in patients with ulcerative colitis before and after IPAA with that in the national population. Methods: Some 258 consecutive women who had undergone IPAA for ulcerative colitis were identified. Data were collected by questionnaire and from medical records. The observed number of births was compared with the number expected by indirect standardization by age and calendar year. Fertility from the age of 15 years to colectomy, from the onset of ulcerative colitis to colectomy, and from the 12 months after stoma closure to the time of data collection was investigated. Results: A total of 237 women (92 per cent) responded. From the age of 15 years to colectomy there were 251 deliveries compared with an expected number of 286 (P 0·3). From the 12 months after ileostomy closure until data collection there were 34 deliveries, compared with an expected 69 (P < 0·001). Conclusion: There is a considerable reduction in postoperative fertility after restorative surgery for ulcerative colitis. © 1999 British Journal of Surgery Society Ltd

Sperm mobility: mechanisms of fertilizing efficiency, genetic variation and phenotypic relationship with male status in the domestic fowl, Gallus gallus domesticus

Abstract: When females are sexually promiscuous, sexual selection continues after insemination through sperm competition and cryptic female choice, and male traits conveying an advantage in competitive fertilization are selected for. Although individual male and ejaculate traits are known to influence paternity in a competitive scenario, multiple mechanisms co-occur and interact to determine paternity. The way in which different traits interact with each other and the mechanisms through which their heritability is maintained despite selection remain unresolved. In the promiscuous fowl, paternity is determined by the number of sperm inseminated into a female, which is mediated by male social dominance, and by the quality of the sperm inseminated, measured as sperm mobility. Here we show that: (i) the number of sperm inseminated determines how many sperm reach the female sperm-storage sites, and that sperm mobility mediates the fertilizing efficiency of inseminated sperm, mainly by determining the rate at which sperm are released from the female storage sites, (ii) like social status, sperm mobility is heritable, and (iii) subdominant males are significantly more likely to have higher sperm mobility than dominant males. This study indicates that although the functions of social status and sperm mobility are highly interdependent, the lack of phenotypic integration of these traits may maintain the variability of male fitness and heritability of fertilizing efficiency.

The impact of the Navrongo Project on contraceptive knowledge and use, reproductive preferences, and fertility.

Abstract: The Navrongo Community Health and Family Planning Project is a quasi-experimental study designed to test the hypothesis that introducing health and family planning services in a traditional African societal setting will introduce reproductive change. This article presents the impact of the initial three years of project exposure on contraceptive knowledge, awareness of supply sources, reproductive preferences, contraceptive use, and fertility. Findings show that knowledge of methods and supply sources increased as a result of exposure to project activities and that deployment of nurses to communities was associated with the emergence of preferences to limit childbearing. Fertility impact is evident in all treatment cells, most prominently in areas where nurse-outreach activities are combined with strategies for involving traditional leaders and male volunteers in promoting the program. In this combined cell, the initial three years of project exposure reduced the total fertility rate by one birth, comprising a 15 percent fertility decline relative to fertility levels in comparison communities.