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At least 19 recordsLinked to original sources
PubMed1991

[Estimates of natural fertility in rural Tokugawa Japan].

"This paper estimates the value of [natural fertility] and [the degree of parity-specific fertility control] in rural Tokugawa Japan mainly using [the Coale-Trussell model]. What we gained through this analysis is 1) the level of natural fertility in rural Tokugawa Japan was very low compared to the pre-transition level of England, [and] 2) in spite of this low level fertility, parity-specific fertility control was not practiced.... We can say that rural Tokugawa Japan since the second half of [the] seventeenth-century was in a 'natural fertility regime'...." (SUMMARY IN ENG)

Asia↗
PubMed1990

What is natural fertility? The remodeling of a concept.

This paper applies three log-linear models to Louis Henry's original 1961 natural fertility data in order to test various assumptions leading to ways of obtaining a standard natural fertility schedule through explicit modeling. "The models specify that births follow an independent Poisson distribution for each age interval of each population. All parameters are estimated through an iterative maximum-likelihood procedure." The author suggests that the model selected provides better estimates of the standard natural fertility function than previous models.

Demography↗
PubMed1980

Natural fertility and associated intermediate variables in some Arab countries.

"This paper will discuss the factors which affect natural fertility in the Middle East and North Africa based on data collected recently in selected countries of the region. First, however, it will consider conceptual approaches to the study of the intermediate fertility variables and problems in applying the concept of natural fertility to contemporary populations."

Africa↗
PubMed1999

Haptoglobin genotype and natural fertility in humans.

OBJECTIVE: To study the possible relation between human natural fertility and haptoglobin (Hp) genotype. DESIGN: Prospective study. SETTING: Maternity departments of local hospitals in two Italian localities. PATIENT(S): Healthy women who had just given birth in the maternity departments of two local hospitals (n = 679). INTERVENTION(S): Venous blood collection for determination of Hp genotype with the use of starch gel electrophoresis of hemoglobin-supplemented serum. MAIN OUTCOME MEASURE(S): Distribution of Hp genotypes in relation to age of puerperae. RESULT(S): In both populations, the proportion of young mothers was much higher among women who were homozygous for the Hp*1 allele (the Hp*1/*1 genotype) than among women who had other Hp genotypes. In addition, the proportion of multiparous women among the older mothers was higher among those with the Hp*1/*1 genotype than among those with other Hp genotypes. CONCLUSION(S): The data suggest that women with the Hp*1/*1 genotype reproduce at an earlier age and have higher natural fertility potential than women with other Hp genotypes.

Adult↗
PubMed1982

A macrosimulation approach to the investigation of natural fertility.

This paper is part of a long-term investigation known as the Mormon Historical Demography Project. It examines the capability of a simulation model, originally proposed by John Bongaarts (1976), to fit the natural fertility pattern which characterized the mid-nineteenth century Mormon population. Application of this model permits estimates to be made of the historical timing and age-incidence of fertility limitation. A sensitivity analysis of the model's parameters demonstrates that simple changes in the model's proximate determinants of fertility, excluding contraceptive practices, would be insufficient to account for later transition effects. Thus the results successfully capture the dynamics underlying the Mormon natural fertility pattern as well as offer a framework for future modeling of the transition away from natural fertility.

Adolescent↗
PubMed1998

The ecology of low natural fertility in Ladakh.

The existence of very low rates of fertility among non-contracepting human populations has intrigued researchers in demography and reproductive ecology. Long inter-birth intervals, driven primarily by the lactational amenorrhoea associated with breast-feeding, have been shown to be important determinants of low natural fertility in several populations. Other reports have suggested that sterility brought about by sexually transmitted diseases (STDs) might also explain low fertility in some populations, especially in Africa. This report presents an analysis of 1981 Indian census data that documents low natural fertility in Ladakh, a high-altitude region of the Himalaya in north India. In Ladakh, there is evidence for low rates of marriage among women that may be attributable to the practice of polyandry, but also high rates of primary and secondary sterility within marriage, resulting in low completed parities for post-reproductive age married women. Age-specific fertility rates derived from the number of current births are also unexpectedly low. Hypotheses to explain very low fertility in Ladakh are considered from among the likely proximate determinants and evaluated using two supplementary sources of information derived from fieldwork in Ladakh in the early 1990s. The most likely explanations for low marital fertility include sterility from STDs, high rates of fetal loss, and possibly nutritional contraints on ovarian hormone status.

Adolescent↗
PubMed1981

Increase in natural fertility during the early stages of modernization: Canadian Indians case study.

It has been hypothesized that populations may experience an increase in their natural fertility during the early stages of modernization as a result of the relaxation of various fertility-inhibiting practices and customs prevalent in traditional societies. This article offers evidence of such an increase in natural fertility among Canadian Indians. The main underlying cause is found to be in the massive, almost abrupt, shift from prolonged breastfeeding to bottlefeeding ;which took place prior to the onset of large-scale birth control practices among Canadian Indians.

Adolescent↗
PubMedDate not supplied

Antral follicle counts are related to age at natural fertility loss and age at menopause.

OBJECTIVE: The variability in ultrasound-based antral follicle counts sized 2-10 mm after allowing for age-related decline is considerable. This may represent differences in actual reproductive age among women. This hypothesis was tested by cohort comparison for distribution of age at occurrence of reproductive events. DESIGN: A model with a nonlinear mean decline with age was fitted to antral follicle counts (AFC) obtained in 163 regularly cycling fertile volunteers. Ages at last child birth and menopause were predicted from the individual AFC by using thresholds to represent these events and the model for decline with age. Distributions of the observed ages at last childbirth (proxy variable for loss of natural fertility) and ages at menopause were obtained from the BALSAC demographic database and the Prospect-EPIC study, respectively. The observed distributions were compared with the predicted distributions by using visual comparison and quantile-quantile plots. Predictions of age at last child and age at menopause were done using percentiles of the modeled AFC distribution for given age, and corresponding percentiles of the predicted distributions of age at these reproductive events, with predictions following from the position of a woman's AFC relative to these percentiles. RESULTS: The predicted distributions of age at last child and age at menopause showed good agreement with the observed distributions in the BALSAC and EPIC cohort. Compared with age alone, antral follicle counts gave some additional information for individual prediction of age at last child and menopause. CONCLUSIONS: The link between declining antral follicle counts and reproductively significant events like loss of natural fertility and menopause is strengthened by the high degree of similarity among the predicted and observed age distributions. Predictive usefulness of this relationship in a clinical setting may be more marginal, except in the case of women who have low AFCs for their age.

Adult↗
PubMed2004

Recovery of natural fertility after grafting of cryopreserved germinative tissue in ewes subjected to radiotherapy.

OBJECTIVE: To recover natural fertility of ewes that were subjected to ovarian failure induced by radiotherapy with an autologous orthotopic graft of cryopreserved germinative tissue. DESIGN: Experimental surgery study. SETTING: University hospital unit. ANIMAL(S): Adult ewes. INTERVENTION(S): Four ewes were submitted to right oophorectomy and posterior dissecting and freezing of the germinative tissue. Afterward, they were administered radiotherapy to induce infertility on the remaining left ovary. Later, two of the ewes had the thawed fragments of the right ovary injected inside the cortex of the irradiated left ovary in a "sowing" procedure that eliminated the need for sutures. MAIN OUTCOME MEASURE(S): Recovery of fertility in ewes after transplantation of germinative tissue into the ovary destroyed by radiotherapy. RESULT(S): The ewes were housed with fertile rams. Six months following the grafting, the rams impregnated the transplanted ewes. More than 2 years after radiotherapy, the nongrafted (control) ewes have not become pregnant. CONCLUSION(S): Intracortical grafting of the germinative tissue circumvents the obstacle of vascular anastomosis with autologous ovarian implants. Patients could benefit from the subcortical grafting of germinative tissue in one of the ovaries, recovering fertility after radiotherapy treatment for malignancy.

Animals↗
PubMed1998

Declining fecundity and ovarian ageing in natural fertility populations.

Worldwide, human fertility declines with increasing maternal age, after contraceptive-use patterns and behavioral factors are taken into consideration. Here, we summarize some of our theoretical and empirical work examining the biological factors contributing to this age pattern of fertility. We undertook an 11 month prospective endocrinological study in a natural fertility (non-contracepting) population (rural Bangladesh) to estimate the contributions of fetal loss and fecundability (the probability of conception) to declining fecundity with age. Prospective interviews and urine samples for pregnancy tests were collected twice weekly from up to 700 women. These data were used to test mathematical models of the underlying biological processes contributing to changing fecundability and fetal loss risk with maternal age. The results indicate that much of the decline in fecundity can be attributed to an increasing risk of fetal loss with maternal age. Much of this fetal loss is due to chromosomal abnormalities--a result of ageing oocytes. Fecundability, on the other hand, does not begin to decline until the early 40s. We hypothesize that this is also a result of ageing at the ovarian level, namely follicular atresia, in the years just prior to menopause. The irregularity of menstrual cycles--longer cycles and increasingly variable hormonal patterns--at these ages may be a direct result of the small and rapidly dwindling remaining pool of follicles. We present a simple mathematical model of this process, and some preliminary laboratory results that support the model.

Adult↗
PubMed2004

Ineffective contraceptive use and its causes in a natural fertility population in southern Jordan.

Based on our interview survey of 574 randomly selected married women from a rural population in the South Ghor district, Jordan, where traditional Arab customs have been persistently maintained, in this paper we analyze the age-specific marital fertility rates (ASMFRs) and contraceptive practices, especially the prevalence and duration of contraceptive use. The ASMFRs fitted the natural fertility pattern proposed by Coale and Trussell's model, and the total fertility rate was estimated to be 7.2. Even though the prevalence rate of modern contraceptive methods has reached 14.3%, because of the recent increase among young women in particular, the users had larger numbers of children than the nonusers and the duration of contraceptive use was short, especially at young ages (e.g., about 90% 24-month discontinuation probabilities in 15-19- and 20-24-year-olds). These ineffective contraceptive uses were related to traditional Arab norms, represented by the pooled proportion of "as many as possible" and "up to God" answers to the ideal number of children (70% of men and 30% of women).

Adolescent↗
PubMedDate not supplied

Natural fertility in northeastern Mexico: genetic structure by year of birth and birthplace.

BACKGROUND: The aims of this population genetics study were 1) to ascertain whether 417 Mexican women with natural fertility (45 years of age, married, not using any family planning methods, residing in the state of Nuevo León) were genetically homogeneous, and 2) to compare the genetic structure of this selected population with the previously reported data of random populations of northeastern Mexico. METHODS: A sample of 417 women was interviewed and selected in seven medical units of the Mexican Social Security Institute. They were grouped by their year of birth (1896-1925 and 1926-1955) and birthplace [persons whose four grandparents were born in the northeastern states (NE) and outside the northeastern states (Not-NE) of Mexico]. Eight genetic marker systems were analyzed. RESULTS: Gene diversity analysis suggests that more than 99.1% of the total gene diversity can be attributed to variation between individuals within the population. Genetic admixture analysis suggests that this selected population, stratified by year of birth and birthplace, have received a predominantly Spanish contribution followed by a lesser Mexican Indian contribution. CONCLUSIONS: The genetic structure of this selected population was homogeneous and similar to the random populations of northeastern Mexico. This finding corroborates the utility of this selected population for genetic and epidemiological studies.

Alleles↗
PubMed1998

Marriage season, promptness of successful pregnancy and first-born sex ratio in a historical natural fertility population--evidence for sex-dependent early pregnancy loss?

We investigated population-based vital records of the seventeenth and eighteenth century French Canadian population to assess the effects of marriage season on the outcome of the first births under natural fertility conditions (n = 21,698 marriages). Promptness of the first successful conception after marriage differed according to marriage season; the proportion of marriages with a marriage-first birth interval of 8.0-10.0 months was lowest (34%) for marriages in August-October (P = 0.001). Although the male/female sex ratio of the babies born with an interval of 8.0-10.0 months was generally higher (1.10) than those with an interval of 10.0-24.0 months (1.05), the marriages in August-October resulted in a significantly reduced sex ratio (0.96) among only the prompt conceptions (P = 0.026). We discuss whether this seasonal reduction of the sex ratio could be partly explained by a clustered pregnancy loss of male zygotes in early pregnancy.

Adult↗
PubMed1995

Slow twin conception at first birth and subsequent maternal twin proneness in a natural fertility population.

To study whether apparently more fecund women having delivered twins at first birth have traits of higher twin-proneness, we performed a retrospective cohort study on population-based historical vital records of the 17-18th century French Canadian immigrants and their descendants under natural fertility conditions. Among 24896 mothers who had at least one child, 248 had twin maternities at their first birth (twinning rate = 1.0%). Among 21508 mothers with a valid marriage-first birth interval, twinning rate was 0.97% among prompt conceptions (7.0-11.0 months), with a particularly high rate at the interval of 7.0-8.0 months (2.2%). Marriages in August-October resulted in a higher twinning rate particularly for the slow conceptions than those in the other seasons. Promptly-conceived mothers of twins at the first delivery may seem to have higher fecundity, but subsequent births from these mothers (n = 88) show a lower twinning rate (1.7%) particularly at younger maternal age than from the other mothers who had slowly conceived twins at their first birth (n = 112). The latter show a 4.5% twinning rate as a whole among their second or later births. So-called twin-proneness of a mother, whether genetic or acquired, was not connected to higher conception rate of twin's mothers immediately after marriage. Reduced fecundity, which may have been imposed by some environmental factors, could raise the chance of twinning.

Adult↗
PubMed1979

From natural fertility to family limitation: the onset of fertility transition in a sample of German villages.

Utilizing data from a sample of German village genealogies, it is possible to document the changes in reproductive patterns on the family level that started to take place in Germany during the nineteenth century and formed the basis for the secular decline in fertility which eventually encompassed the entire country. One striking finding from this study was the substantial diversity among the small sample of villages in terms of the timing of the emergence of family limitation. While couples in all villages who married during the last half of the eighteenth century appeared to be characterized predominantly by natural fertility the emergence of family limitation began as early as the turn of the nineteenth century in some places and as late as the end of the nineteenth century in others. Occupational differentials with respect to family limitation were also examined. There is little evidence that changes in birth spacing played an important part in the initial phase of the fertility trnsition. Rather, the underlying process appears to involve a change from fertility patterns that were characterized by the absence of parity-dependent control to one in which attempts to terminate childbearing in response to the number of children already born becomes widespread.

Age Factors↗