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Results for “Fertility Rate--changes”

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PubMed1996

A model conforming the decline in follicle numbers to the age of menopause in women.

The store of primordial follicles in the ovary is fixed before birth and dwindles with age until it is unable to provide enough Graafian stages to sustain menstrual cyclicity. According to a simple bi-exponential model of ageing, the rate of follicle disappearance increases at age 37.5 years (or when 25 000 follicles remain) so that the numbers fall to approximately 1000 at 51 years, the median age of menopause in the population. This study attempts to produce a biologically more realistic model of follicle disappearance and harmonizes follicle dynamics with the distribution of menopausal ages from an American survey. The step-change in the rate of follicle attrition was replaced by a model which assumed that this rate changes more gradually with the size of the follicle store. This produced a distribution of predicted menopausal ages (based on an assumed threshold of 1000 follicles) which was closer to observed data. The fit further improved when the model was modified by having a threshold that varied across the population. Using such a stochastic threshold model for menopause, the number of fertile years remaining could be forecast with an acceptable margin of uncertainty if it ever becomes possible to estimate the size of the follicle store in vivo.

Adult↗
PubMed2002

Delayed childbearing and its impact on population rate changes in lower birth weight, multiple birth, and preterm delivery.

OBJECTIVE: This study quantified the impact of delayed childbearing (maternal age greater-than-or-equal to 35 years) on population rate changes in low birth weight (LBW; < 2500 g), preterm delivery (< 37 weeks), multiple births, and small for gestational age (SGA; < 10th percentile) in Alberta, Canada, between 1990 (N = 42 930) and 1996 (N = 37 710). METHODS: Data were obtained from the provincial notification of a live or stillbirth. Analyses included relative risk estimates and chi(2) tests for trend. Potential confounding attributable to in vitro fertilization was investigated. RESULTS: The proportion of births to women greater-than-or-equal to 35 years of age was 8.4% in 1990 and 12.6% in 1996, a 51.2% increase. Among these women, LBW delivery increased 11%, and preterm delivery increased 14%. Delayed childbearing accounted for 78% of the change in LBW rate in the population and 36% of the change in preterm delivery rate in the population. Provincial multiple birth rates increased by 15% for twins and 14% for triplets. Delayed childbearing accounted for 15% of the twin increase and 69% of the triplet increase. When in vitro fertilization pregnancies were excluded, the change was 43% for preterm rates, 100% for LBW, 14% for twins, and 9% for triplets. Delayed childbearing did not contribute to changes in singleton SGA deliveries. CONCLUSIONS: The findings suggest that the recent increase in LBW and preterm delivery is partly related to the population phenomenon of delayed childbearing. Maternal age was not related to changes in SGA, suggesting that the age effect is through pregnancy complications that lead to preterm delivery and LBW. Prospective parents should be informed about the higher risk for neonatal morbidity associated with delayed childbearing. Health care providers should be aware of the impact of delayed childbearing on health care resources.

Adult↗
PubMed1998

Probabilities for singleton and multiple pregnancies after in vitro fertilization.

OBJECTIVE: To help physicians provide risk estimates for specific pregnancy outcomes. DESIGN: Computation of exact binomial probabilities for singleton and multiple pregnancies as a function of two inputs: the number of embryos transferred and the implantation rate. Inputs were varied over the range of values reported in the literature. MAIN OUTCOME MEASURE(S): Probabilities for a singleton pregnancy (none), a multiple pregnancy (Pmult), and no pregnancy (Pnone) after one IVF cycle. RESULT(S): Given a 30% implantation rate and three embryos transferred, Pone=.44, Pmult=.22, and Pnone=.34. Although further increasing the number of embryos transferred increases the chance of pregnancy, it also raises the probability of a multiple pregnancy and lowers the chance of a singleton pregnancy. Although varying the implantation rate changes the specific probability estimates, the same trade-off persists. CONCLUSION(S): Those who consider an IVF "success" to be a singleton pregnancy should be attentive to the number of embryos transferred. Infertility therapy may be one area in medicine where more is not necessarily better.

Adult↗
PubMed1980

Breast cancer in Greenland--selected epidemiological, clinical, and histological features.

Fifty-seven breast cancers were diagnosed among indigenous Greenlandic women from 1950 to 1974. An additional 22 cases registered between 1975 and 1979 represent a minimum number and were only used as basis for minimum incidence rates. Changes in age-adjusted rate, age-specific incidence pattern, and relative risk were consistent with an upward shift from a population of low risk between 1950 and 1969 to one of intermediate risk from 1970 onward, a finding that relates well to increased urbanization and westernization. The risk of breast cancer in Greenland may be associated with consumption of saturated fats but is seemingly not correlated to total fat intake which has always been on a par with high-risk Danish levels. An association with diet may in reality have been stronger than suggested but weakened by a counterbalancing effect of high fertility, especially in the youngest age groups. Evaluation of histological features and survival did not suggest differences which could favorably compare with findings in white population groups contrary to reported results from the population of Japan, also one of low risk and of mongoloid origin. Further studies should consider dietary intakes, endocrine variations, and breast fluid secretion with special attention to girls at the age of menarche.

Adult↗
PubMed2000

Seven-year trends in HIV-1 infection rates, and changes in sexual behaviour, among adults in rural Uganda.

OBJECTIVE: To assess trends in HIV-1 infection rates and changes in sexual behaviour over 7 years in rural Uganda. METHODS: An adult cohort followed through eight medical-serological annual surveys since 1989-1990. All consenting participants gave a blood sample and were interviewed on sexual behaviour. RESULTS: On average, 65% of residents gave a blood sample at each round. Overall HIV-1 prevalence declined from 8.2% at round 1 to 6.9% at round 8 (P = 0.008). Decline was most evident among men aged 20-24 years (11.7 to 3.6%; P < 0.001) and women aged 13-19 (4.4% to 1.4%; P = 0.003) and 20-24 (20.9% to 13.8%; P = 0.003). However, prevalence increased significantly among women aged 25-34 (13.1% to 16.6%; P = 0.04). Although overall incidence declined from 7.7/1000 person-years (PY) in 1990 to 4.6/1000 PY in 1996, neither this nor the age-sex specific rates changed significantly (P > 0.2). Age-standardized death rates for HIV-negative individuals were 6.5/1000 PY in 1990 and 8.2/1000 PY in 1996; corresponding rates for HIV-positive individuals were 129.7 and 102.7/1000 PY, respectively. There were no significant trends in age-adjusted death rates during follow-up for either group. There was evidence of behaviour change towards increase in condom use in males and females, marriage at later age for girls, later sexual debut for boys and a fall in fertility especially among unmarried teenagers. CONCLUSIONS: This is the first general population cohort study showing overall long-term significant reduction in HIV prevalence and parallel evidence of sexual behaviour change. There are however no significant reductions in either HIV incidence or mortality.

Adolescent↗
PubMed1983

The family and the reproduction of the population.

"The causes for the lowering of the birthrate below the necessary level for a simple reproduction of society [in the USSR are] sought within the family itself and in the conditions surrounding its existence....The present demographic situation requires the elaboration of a whole program for the development of marital and family relationships and the optimization of population reproduction processes....[Such a program] must encompass the issues of preparing youth for family life, the prestige of the family and its economic status, the optimal distribution of functions among individuals in the family and in society,....[and] the equalization of per capita income levels between one-child and large families...."

Birth Rate↗
PubMed1991

Abortion in South Australia, 1971-86: an update.

Official statistics on abortion in South Australia for the period 1971-86 are analysed in terms of incidence, age of patients and nuptiality, reasons for abortion, method of termination, period of gestation, previous abortions and concurrent sterilisation. Demographic implications are discussed and recommendations are made for more education and counselling, especially for younger and unmarried women for whom the incidence of abortion seems to be rising.

Abortion, Induced↗
PubMed1991

Trends in the contraceptive practices of women seeking abortions in the 1980s.

The demographic features and contraceptive practices of 1000 women attending Parkview clinic of Wellington Hospital for termination of pregnancy were studied over an eight month period in 1988-9. Comparisons were made with a previous study at the same clinic in 1980-1. The overall abortion rate has increased from 6.8/1000 women in the Wellington statistical area in 1981 to 9.8 in 1989. The proportion of Pacific Island and Asian women presenting for abortions is high and has increased disproportionately between 1981 and 1989. The abortion rate has also increased in lower socioeconomic groups in 1989. The proportion of women using contraception at the time of conception increased from 50% in 1981 to 68.5% in 1989. The methods used by women presenting for abortion have changed significantly. There has been an increase in the proportion of women using condoms (from 13.3% to 36.2%) and the oral contraceptive pill from (14% to 21.4%).

Abortion Applicants↗
PubMedDate not supplied

Contraceptive paths toward the reduction of unintended pregnancy and abortion.

Based on data from the 1982 National Survey of Family Growth, exposure to the risk of unintended pregnancy is classified by use of specific contraceptive methods and by nonuse, and average rates of unintended pregnancy are estimated for each type of exposure. Three hypothetical models of improved contraceptive practice are then applied to the data for all women and for age, race and marital-status subgroups. The first two models assume increases in the use of some existing contraceptive methods, but only the second model additionally assumes the introduction of new methods. The third model assumes the complete elimination of nonuse of contraception. These models yield different estimates of the reduction in unintended pregnancy rates which are illustrated for various age-groups, for whites and blacks and for married and unmarried women. Among all women aged 15-44, the changes assumed by Model I imply a 32 percent reduction in unintended pregnancy; Model II implies a 56 percent reduction; and Model III implies a 57 percent reduction. The implied reductions in abortion are in a similar range.

Abortion, Induced↗