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We investigate the use of control theory in population planning and show how the use of age at first birth, birth interval, and sex ratio as control variables leads to a practical, fault tolerant approach to population planning and control.
In this experiment, 98 multiparous Yorkshire sows blocked on farrowing date were randomly assigned to four treatments in a 2 x 2 factorial arrangement. Oxygen inhalation (6 L/min) by the sow was tested in an effort to reduce stillbirth rate and improve pig viability. This study also tested the effect of increasing uterine contractions using neostigmine (5 mg) to determine whether simultaneous administration of oxygen to the sow could improve the inconsistent response of stillbirth rate to neostigmine. Pig viability was assessed using viability scoring and blood gas analysis of samples obtained from the suborbital sinus immediately after birth. The farrowings averaged 12.2 pigs/litter, 7.8% stillbirths, and 3.5% low viability (viability score < or = 6) pigs. Treatment had no effect on stillbirth rate or pig viability. Oxygen treatment increased pO2 (P = .0002), increased pCO2 (P = .02), and decreased pH (P = .02) in sow venous blood sampled after the birth of the last pig, but it had no effect on pig venous blood gases. Neostigmine treatment had no effect on either sow or pig venous blood gases. Oxygen treatment doubled the length of the first birth interval after the start of treatment (P = .003) but had no effect on remaining birth intervals. Neostigmine had no effect on birth interval. It is suggested that the effect of oxygen on birth interval is the reason for the lack of improvement in stillbirth rate.
The impact of female employment on fertility preferences and behavior is examined with data from a 1980 national sample of Taiwanese women. The guiding hypothesis is that the greater the involvement of women in the impersonal market sector, the lower the fertility preferences, the longer the first birth interval, and the lower the actual fertility. Findings reveal that female employment in Taiwan is only weakly related to reproductive behavior. Even with increased participation of women in the modern market sector, female employment apparently has little impact on fertility preferences or behavior. Implications are drawn for policies aimed at lowering fertility.
This paper develops a multistate hazards model for estimating fecundability and sterility from data on waiting times to conception. Important features of the model include separate sterile and nonsterile states, a distinction between preexisting sterility and sterility that begins after initiation of exposure, and log-normally distributed fecundability among nonsterile couples. Application of the model to data on first birth intervals from Taiwan, Sri Lanka, and the Amish shows that heterogeneity in fecundability is statistically significant at most ages, but that preexisting sterility and new sterility are unimportant before age 40. These results suggest that sterility may not be an important determinant of natural fertility until later reproductive ages.
In this article, we introduce an alternative technique to the single-sentence question for measuring preferences for number of children, age at marriage, length of first birth interval, length of employment, and years of schooling. This new measurement procedure utilizes a graphic scale rather than verbal responses, and it places family size decisions within the context of several other major life cycle decisions. One month reliability data for the measurement technique were obtained from a sample of 107 school children. Reliability results are compared to data from a previous study of teenagers.
We investigated the impact of a long interval between the birth of the first and the second twin on second twin perinatal mortality (PNM). National data in the Swedish Medical Birth Registry were used on 7533 second twins born in Sweden between 1973 and 1985. PNM as a function of the time interval between the births of the twins was studied in data from two time periods: during 1973-78 (n = 4008) and 1979-85 (n = 3525). During the first period, PNM was significantly higher at intervals of 30 min or more between the births of the twins than at shorter intervals (chi 2 = 11.1, p less than 0.001). When studied within broad birth weight classes, a significant trend was seen for twins weighing 1500-2499 g with an increasing interval (chi 2 = 8.1: p less than 0.01). A non-significant trend was also found for twins weighing less than 1500 g but none for twins weighing greater than or equal to 2500 g. During the second period, abdominal delivery of the second twin after vaginal delivery of the first twin was significantly more common than during the first period (2.0% vs 0.3%, chi 2 = 52.7, p less than 0.001). During the second period, the interdelivery interval had little impact on second twin PNM. The results of this study seem to indicate that with modern management of labor and delivery, as seen in Sweden since 1979, the interdelivery interval has little impact on second twin PNM.
We studied the time interval to the first birth and to the twin birth using statistical and mathematical models in two groups of mothers, those with twins and those with singletons, from the same population. We made use of a pair-matched case-control design. We treated the maternal birth cohort and parity as confounders and thus as controlled. We also investigated the sex of twin pairs as an interactive variable, employing such methods as survival curve testing and using geometric, gamma, and exponential distributions where appropriate. The expectations derived from the mathematical models yield numerical estimates of fertility components. The results suggest that unlike-sex twin-prone mothers have higher fecundity than controls when they conceive singletons. Further, fecundity appears high and unimpaired before the birth of twins. Mothers of like-sex twins experience somewhat shorter and but more variable birth intervals than corresponding controls before the birth of twins, suggesting within-group heterogeneity. Specifically, the birth of like-sex twins is preceded by low fecundity and a short period of postpartum amenorrhea. Biologically, like-sex (presumably monozygotic) twin-prone mothers have a hormonal defect related eventually to menopausal status that interferes with ovulation and perhaps with lactation. As for unlike-sex twin-bearing mothers, they probably experience a displacement of their maximum fertility potential toward early reproductive life and an extension of their menstrual life. From a methodologic standpoint, the study of the fertility of twin-prone mothers cannot proceed without estimates of the fertility components of birth intervals, as these intervals do not lend themselves to straightforward analytical interpretations by statistical analyses.
In Canadian society the influence of first birth timing on the subsequent birth interval has been eroded over time, as shown by the Canadian Fertility Survey of 1984. The influence of first birth timing is significant for second births among women married during the baby boom period, but not for those married thereafter. Religiosity, marital status, and place of residence are significant factors in second birth timing in Canada.
"Based on some simple assumptions regarding [the] human reproduction process, a continuous time stochastic model for describing the variation in any closed birth interval of a woman of marital duration (t) has been developed. The model incorporates the possibility of the variation of the amenorrhea period among the women under observation. For illustration, the model is applied to an observed closed birth interval between first and second births of the women with marital duration of seven years."
Based on long-term, although intermittent, observations (2 years 4 months of 14 years), we present data on birth seasonality, age at first birth, interbirth intervals, mortality rates, age at first emigration, and population change of a wild population of West African patas monkeys ( Etythrocebus patas patas) in northern Cameroon. Birth season was from the end of December until the middle of February, corresponding to the mid-dry season. In spite of large body size, the patas females had the earliest age at first birth (36.5 monthsold) and the shortest interbirth intervals (12 months) compared to the closely related wild forest guenons. Age at first emigration of the males was considered to occur between 2.5 and 4.5 years. The group size of the focal group drastically decreased between 1984 and 1987, and steadily increased until 1994, then decreased again in 1997. The neighboring group also showed a similar trend in group size. The population decreases were likely to be caused by drought over 3 years. Annual crude adult mortality rate was 4% during population increase periods (PIP) between 1987 and 1994. It rose to 22% during all the periods (AP), including drought over 3 years. Despite their smaller body size, the rate of the wild forest guenons ( Cercopithecus mitis) (4%) was the same and much lower than those of the patas during PIP and AP, respectively. The annual average juvenile mortality rate was 13% during PIP and it also rose to 37% during AP. That of wild forest guenons ( C. ascanius) (10-12%) was a little lower and much lower than those of the patas during PIP and AP, respectively. These findings were consistent with Charnov's theoretical model of mammalian life-history evolution in that patas with high adult and juvenile mortality showed early and frequent reproduction in spite of large body size. Charnov also considered high adult mortality as a selective force and high juvenile mortality as a density-dependent consequence of high fecundity. Our results support the former but not the latter research findings.
The Utah (United States) Population Database was used to evaluate the associations between reproductive factors and colon cancer risk and the impact that family history, age at diagnosis, and tumor site have on these associations. From the cohort of (White) women in the database, all first-primary cases of colon cancer (n = 819) and controls who had complete fertility information (n = 3,202) were examined. The majority of tumors (68.6 percent) among women diagnosed at age 64 years or less were in the distal segment of the colon, while among women 65 or older, the majority of tumors (55.7 percent) were proximal. Women diagnosed before age 65 had a lower risk of colon cancer with increasing numbers of liveborn children (odds ratio [OR] = 0.6, 95 percent confidence interval [CI] = 0.3-0.9 for women with five or more children compared with women with one or two children). A long interval between first and second births (first birth-interval) was associated with increased risk of tumors in the distal segment of the colon (OR = 1.4, CI = 1.0-2.0) and among women diagnosed before age 65 (OR = 1.6, CI = 1.0-2.5); a longer, average birth-interval was associated with increased risk of proximal tumors (OR = 1.5, CI = 1.1-2.1).(ABSTRACT TRUNCATED AT 250 WORDS)
OBJECTIVES: Parity is known to induce protective effects on ovarian cancer. This study aimed to evaluate how far upon births the protection reaches, the effect of age at first birth, the interval between births in the whole population and the length of time from the first to the last birth and from the last birth to cancer among postmenopausal women. METHOD: The population-based cohort consisted of 87,929 grand multiparous (GM) women, i.e. women with at least 5 deliveries. Standardised incidence ratios (SIRs) were calculated by dividing the number of observed cancer cases by the expected number based on the national incidence rates, both extracted from the population-based Finnish Cancer Registry. Conditional logistic regression for the case-control design nested in the GM cohort was used to estimate proportional hazards by different factors. RESULTS: The SIR for ovarian cancer among GM women was low (418 cases; SIR 0.64, 95% confidence interval 0.58-0.69). Further births over five did not give additional protection. The relative risk did not vary significantly by age at first birth or interval between the births in any histological subtype. CONCLUSION: The risk of ovarian cancer was low in all GM women no matter how many children and at which ages they had delivered or contracted cancer.
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Reproductive patterns were studied from data collected in 1,450 Berber households in the province of Marrakesh, Morocco in 1984. Women aged 45-49 years had a mean of 8.9 pregnancies to achieve 5.7 living children. Social influences on fertility rates show the importance of tradition, particularly through time-dependent variables such as age at marriage, waiting time to first birth, interbirth intervals, and duration of breastfeeding. Birth control does not appear to affect the tempo of fertility; rather, its main use is to bring the reproductive period to a close. The comparison of two subsamples of women separated by a 25-year interval indicates an actual acceleration of the tempo of fertility by the reduction of waiting time to first birth and of interbirth intervals. The supposed ongoing process of demographic transition is not clearly observed in this population.
PURPOSE: To examine factors associated with the number of prenatal care visits during second pregnancy for adolescents having a short interval between pregnancies. METHODS: The sample includes all adolescents aged 13 to 17 years whose first pregnancy resulted in a birth at a regional medical center in southeastern North Carolina from January 1983 to December 1989 and who had a repeat pregnancy within 24 months which resulted in a birth. We abstracted data from medical records and birth certificates. We fit a negative binomial regression model to determine the effects of various factors on the number of prenatal care visits during second pregnancy. RESULTS: The number of prenatal care visits during the first pregnancy, poor first birth outcome, interval between first and second pregnancy, and care provided by health department staff during first pregnancy were all positively associated with number of prenatal care visits during second pregnancy when controlling for gestation age of second birth. Other independent variables in the model included maternal age, education, black race, and being unmarried at the time of second birth. CONCLUSIONS: Because prenatal care is important for healthy mothers and babies, adolescents should be encouraged to seek prenatal care early in the first pregnancy. This could be an important time to implement interventions aimed at increasing prenatal care utilization in this and subsequent pregnancies.
OBJECTIVE: To assess the influence of parity on the clinical and biological features of systemic sclerosis (SSc). METHODS: We recorded the following clinical and biological data of 100 consecutive women with SSc: age, disease duration before diagnosis, cutaneous extension of sclerosis according to LeRoy's classification, pulmonary involvement, and antinuclear antibodies. We compared these features to the number and sex of children who were born before SSc onset. Date of birth of the first children was systematically recorded. RESULTS: Patients with limited SSc had more children before SSc onset than patients with diffuse SSc (2.4 +/- 1.8 vs 1.7 +/- 1.5; p < 0.05). The interval between first birth and SSc onset was shorter for patients with limited SSc than for patients with diffuse SSc (11.0 +/- 9.9 vs 23.5 +/- 14.5 yrs; p < 0.01). Patients with pulmonary fibrosis had more children than patients without pulmonary fibrosis (2.5 +/- 1.9 vs 2.0 +/- 1.6; p < 0.05). Age at first birth was significantly higher when the child was a girl than a boy (26.8 +/- 7.5 vs 22.9 +/- 5.3 yrs; p < 0.05). The interval between the first birth and SSc onset was shorter when the child was a girl than a boy (16.2 +/- 9.6 vs 25.4 +/- 13.4 yrs; p < 0.05). CONCLUSION: Pregnancy related microchimerism could be preferentially associated with limited SSc and pulmonary fibrosis. Microchimerism may be facilitated in cases in which the fetus is female.
The paper describes methodology for doing nutrition surveys among deprived population groups of grossly homogeneous socioeconomic status so as to identify those families in which a child between age six months and five years falls in the upper 25 per cent in height and weight measurements. These families are labeled as being "Positive Deviants" from the undernutrition that prevails in the population. They are then studied anthropologically to uncover any practices related to food sources, storage, preparation, consumption, and content. The information would be used in designing food supplementation or other nutritional promotion in the population at large on the assumption that the observed "favorable" practices, although atypical, are feasible and culturally acceptable because they are indigenously rather than extraneously derived. In addition, the survey collected data on fertility because of findings concerning the close interrelatedness among a woman's nutritional state, her age when first giving birth, intervals between births, and the growth and development of her young children. Severe undernutrition raised a woman's safe age threshold for first birth above 20 years and a reasonably safe birth interval to more than three years.
Biological fertility is poorly measured by the number of children born in industrially advanced societies. The time elapsing from when a couple decides to have a child to clinically recognizable pregnancy is a useful alternative. Time to pregnancy can be collected in broad categories in large samples. A model for condensing important information from such data is presented, which fits several large samples of reported waiting times. It is shown that multiparous women conceive more quickly than primiparous women.