Birth interval, mortality and growth of children in a rural area in Kenya

The impact of the length of birth intervals on mortality and growth of children from the perinatal period to 2 years in the Northern Division of Machakos District, Eastern Province, Kenya, were analyzed. There are 2 types of birth intervals: 1) the prospective birth interval--between the birth concerned (the 1st birth of the interval pair) and the subsequent birth; and 2) the retrospective birth interval--between the birth considered (the 2nd of the interval pair) and the preceeding birth. This study includes 3019 women who had at least 1 live birth between April, 1974 and April, 1981. They gave birth to 6778 children (including stillbirths). Births occurring in 1974 are excluded in the analysis because of considerable underregistration. 102 stillbirths and 213 deaths in the 1st 2 years are analyzed. They have been grouped into deaths during the perimatal period; the 1st year after the 1st week of life (infant period); and the 2nd year of life. The most convient method of analysis of the relation between retrospective birth interval and mortality is multivariate analysis, as the intermedicate biological and behavioral factors through which birth intervals can affect health are simultaneously influenced by other variables like maternal age and birth order; the log linear model is applied here. The probability of dying is the dependent variable. The impact of short prospective intervals are closely associated. Only infant and child deaths occurring after the conception of the next child are included. The size of cohorts in which these deaths occur can be calculated with a life table approach. The mortality probability between 5 and 12 months for children with short prospective intervals is .034. This is higher than the corresponding rate for all children in the area (P0.05). It is shown that children with short retrospective or prospective birth intervals do not run a greater risk of mortality or growth retardation than children with longer intervals, neither during the perinatal period nor during the 1st 2 years of life.     

Birth spacing in Pakistan

Life table analysis was applied to data from the 1975 Pakistan Fertility Survey to identify child spacing differentials between population subgroups. Women in urban areas had shorter birth intervals than their rural counterparts from parities 1-6; only after parity 7 was this differential reversed. Similarly, women with some education had shorter birth intervals at the earlier parities than uneducated women. While overall family size is relatively homogeneous in Pakistan, women of more modern backgrounds seem to space their children more closely than traditional women. Age at marriage appears to play an important role not only in determining the length of the 1st interval, but also that of subsequent intervals. An unexpected finding was that ever users of contraception had distinctly more rapid spacing of their births than never users. The median interval to 1st birth was shortest in North West Frontier Province, but similar in Punjab and Sind. Multiple classification analysis revealed that some differentials in child spacing by education, residence, and province persisted even after other variables were controlled. Cohort of mother had an independent effect, with younger cohorts having shorter birth intervals. However, the variable that had the strongest effect on length of interval (aside from the 1st interval) was breastfeeding duration. It is likely that increasing urbanization and improved levels of education among women will lead to high levels of marital fertility associated with shorter birth intervals. Even though these trends tend to increase the age at marriage, they are associated with shorter durations of breastfeeding. In the longer term, greater use of contraception among women in the modern sector may partially counteract the fertility increasing effect of reduced birth intervals.     

Determinants of intrauterine growth retardation: evidence against maternal depletion

This analysis examines the relationship between length of preceding birth interval and risk of intrauterine growth retardation using data on Swedish infants from the 1973 World Health Organization study of perinatal mortality. Results of a multivariate logit analysis demonstrate that the lower than average mean birth weight of infants born after short birth intervals cannot be completely attributed to their shorter mean gestation length. Infants born after birth intervals of 12 months or less are 30% more likely to be small for gestational age (SGA) than infants born 18-59 months after the previous birth, even when the effects of maternal age and parity are controlled. The results obtained here do not support maternal depletion as an explanation for the association between short birth intervals and elevated risk of SGA, since there is no evidence of an attenuation of the risk of SGA with increasing length of interval in the under 18 month birth interval range.     

Reduced birth intervals following the birth of children with long-term illness: evidence supporting a conditional evolved response

Human birth interval length is indicative of the level of parental investment that a child will receive: a short interval following birth means that parental resources must be split with a younger sibling during a period when the older sibling remains highly dependent on their parents. From a life-history theoretical perspective, it is likely that there are evolved mechanisms that serve to maximize fitness depending on context. One context that would be expected to result in short birth intervals, and lowered parental investment, is after a child with low expected fitness is born. Here, data drawn from a longitudinal British birth cohort study were used to test whether birth intervals were shorter following the birth of a child with a long-term health problem. Data on the timing of 4543 births were analysed using discrete-time event history analysis. The results were consistent with the hypothesis: birth intervals were shorter following the birth of a child diagnosed by a medical professional with a severe but non-fatal medical condition. Covariates in the analysis were also significantly associated with birth interval length: births of twins or multiple births, and relationship break-up were associated with significantly longer birth intervals.     

Birth spacing in langur monkeys (Presbytis entellus)

This paper presents 10 years of reproductive data on birth interval length and 5 years of data on reproductive behavior postpartum from a captive colony of gray langur monkeys (Presbytis entellus)housed in Berkeley, California. Birth intervals of females following different pregnancy and nursing schedules are compared. Females whose infants survive to the age of 9 months have a median birth interval of 15.4 months. The experimental separation of mothers from infants for a period of 2 weeks, 6 to 9 months postpartum, had no significant effect on the median birth interval length. Females experiencing a pregnancy failure or the loss of a neonate had median birth intervals of 9.6 and 10.7 months, respectively. These intervals were significantly shorter than the birth intervals of females whose infants survived to 9 months, showing that the presence of a nursing infant delays the female’s time to next conception by approximately 5 to 6 months. Females experienced a median of three estrous periods (two estrous cycles) before conceiving postpartum, regardless of pregnancy outcome or length of infant survival, and females rarely conceived during their first estrous period postpartum. Weaning did not occur until after the mother’s next conception. These data indicate that, in populations of langurs characterized by average birth intervals of 15 to 16 months, the loss of an infant after the age of 5 to 6 months will not accelerate a female’s ability to conceive or shorten the birth interval length. The available data on birth spacing from populations of free-ranging langurs are reviewed. It could not be demonstrated that non-Himalayan populations are characterized by birth intervals which are as long as 20 to 24 months. Rather, it is suggested that female langurs inhabiting seasonally arid sites, such as Jodhpur, Abu, and Dharwar, may be capable of producing infants on the average of every 15 to 16 months. Flexibility in the timing of births and the lack of well-defined birth seasons at these sites may be explained by this species’ dietary and digestive adaptations. Additionally, data on birth spacing and the age of missing infants from the above field sites, where it has been suggested that infanticide following changes in male leadership occurs habitually, do not lend support to the sexual selection hypothesis of infanticide as proposed by S. Hrdy (1974, 1977).     

Age at return marriage and timing of first birth in India's Uttar Pradesh and Kerala states

Abstract

The study investigates the relationship between age at marriage and the length of first birth interval in two states of India: Uttar Pradesh and Kerala. Life tables of first‐birth intervals and median first‐birth intervals are computed for several subgroups of the study population. Multivariate hazards modelling technique is used to study the net effect of age at marriage, controlling for a multiple of socioeconomic factors. The result shows that the average first‐birth interval varies by age at marriage and is much longer in Uttar Pradesh than in Kerala.     

Dependency plots suggest the kinetic structure of ion channels.

Ion channels are integral membrane proteins that regulate ionic flux through cell membranes by opening and closing (gating) their pores. The gating can be monitored by observing step changes in the current flowing through single channels, and analysis of the observed open and closed interval durations has provided a window to develop kinetic models for the gating process. One difficulty in developing such models has been to determine the connections (transition pathways) among the various kinetic states involved in the gating. To help overcome this difficulty we present a transform (dependency plot) of the single-channel data that can give immediate insight into the connections. A dependency plot is derived by calculating a contingency table from a two-dimensional (joint density) dwell-time distribution of adjacent open and closed intervals by assuming that the two classified criteria are the open and closed durations of each pair of adjacent intervals. A three-dimensional surface plot of the fractional difference between the numbers of observed interval pairs and the numbers expected if the durations of adjacent intervals are independent then gives the dependency plot. An excess of interval pairs in the dependency plot suggests that the open and closed states (or compound states) that give rise to the interval pairs in excess are directly connected. A deficit of interval pairs suggests that the open and closed states (or compound states) that give rise to the interval pairs in deficit are either not directly connected or that there are additional open-closed transition pathways arising from the directly connected states.     

Analysis of birth intervals in a non-contracepting Indian population: an evolutionary ecological approach

Reproductive strategies are related to ecological constraints. This paper examines data on early birth spacing in a scheduled caste, Bengali-speaking, non-contracepting population of the Karimganj district of southern Assam, India, taking an evolutionary ecological perspective. It is found that on average birth intervals closed by boy-boy are longer than those closed by girl-girl. Birth spacing tends to be longer among upper-income and Craftsman sub-caste mothers. The presence of a 'grandmother' in the household shortens spacing. These findings are compatible with an evolutionary-based reproductive decision-making process.     

The impact of labor-saving technology on first birth intervals in rural Ethiopia

Across the developing world labor-saving technologies introduce considerable savings in the time and energy that women allocate to work. Hormonal studies on natural fertility populations indicate that such a reduction in energetic expenditure (rather than improved nutritional status alone) can lead to increased ovarian function. Other qualitative studies have highlighted a link between labor-saving technology and behavioral changes affecting subsequent age at marriage, which may affect fertility. This biodemographic study was designed to investigate whether these physiological and behavioral changes affect fertility at a population level by focusing on a recent water development scheme in Southern Ethiopia. The demographic consequences of a reduction in women's workload following the installation of water points, specifically the variation in length of first birth interval (time lapsed between marriage and first birth), are investigated. First birth interval length is closely associated with lifetime fertility in populations that do not practice contraception, longer intervals being associated with lower fertility. Using life tables and multivariate hazard modeling techniques a number of significant predictors of first birth interval length are identified. Covariates such as age at marriage, season of marriage, village ecology, and access to improved water supply have significant effects on variation in first birth intervals. When entered into models as a time-varying covariate, access to a water tap stand is associated with an immediate reduction in length of first birth intervals.     

Age at return marriage and timing of first birth in India's Uttar Pradesh and Kerala states.

The study investigates the relationship between age at marriage and the length of first birth interval in two states of India: Uttar Pradesh and Kerala. Life tables of first-birth intervals and median first-birth intervals are computed for several subgroups of the study population. Multivariate hazards modelling technique is used to study the net effect of age at marriage, controlling for a multiple of socioeconomic factors. The result shows that the average first-birth interval varies by age at marriage and is much longer in Uttar Pradesh than in Kerala.     

Time and space distribution of coincident impulses in closed neural circuits in the sensorimotor cortex of the rabbit (the rhythmical defensive dominanta)

In the course of analysis of the conjugate unit activity of simultaneously recorded neurons in the sensorimotor cortex of rabbits, 22 closed neural circuits consisting of 3 or 4 neurons were considered. In the model of the defensive dominanta, 1-3 weeks after imposing rhythmic (2 s) activity to a rabbit, the distribution of coincident impulses was analyzed in real time. It was found out that the events when the coincident impulses of neural pairs were generated with two-second intervals could be shifted in time and space over a closed circuit of neurons in one direction. Two-second intervals between the coincident impulses of the neighboring pairs could be conjugate, i.e. the end of one interval in one pair coincided with the beginning of a two-second interval in the next pair. Conjugate intervals of the neighboring neural pairs could promote a pass-through of the information on the stimulus properties over the closed neuronal circuit, thus completing a full cycle. The longest passes-through lasted from 10 and 12 s. Also, more intricate variants of the information transfer were revealed. Thus, not only passes-through of the two- second intervals between the neuronal pairs were observed, but also, coincident impulses repeatedly occurred with this interval in some of the pairs of the circuits. The longest transitions lasted 16 and 22 s.     

Association between Birth Interval and Cardiovascular Outcomes at 30 Years of Age: A Prospective Cohort Study from Brazil

Background

Birth interval is an important and potentially modifiable factor that is associated with child health. Whether an association exists with longer-term outcomes in adults is less well known.

Methods

Using the 1982 Pelotas (Brazil) Birth Cohort Study, the association of birth interval with markers of cardiovascular health at 30 years of age was examined. Multivariable linear regression was used with birth interval as a continuous variable and categorical variable, and effect modification by gender was explored.

Results

Birth interval and cardiovascular data were present for 2,239 individuals. With birth interval as a continuous variable, no association was found but stratification by gender tended to show stronger associations for girls. When compared to birth intervals of <18 months, as binary variable, longer intervals were associated with increases in height (1.6 cm; 95% CI: 0.5, 2.8) and lean mass (1.7 kg; 95% CI: 0.2, 3.2). No difference was seen with other cardiovascular outcomes.

Conclusions

An association was generally not found between birth interval and cardiovascular outcomes at 30 years of age, though some evidence existed for differences between males and females and for an association with height and lean mass for birth intervals of 18 months and longer.     

Lactation and interbirth interval in the Senegal galago (Galago senegalensis moholi)

Five years of reproductive data on Galago senegalensis moholi at the Duke University Primate Center were examined to determine the effect of lactation on interbirth interval and its component phases, postpartum anovulatory interval and interval from onset of estrous cycles to conception. Females whose infants died within 3 weeks of birth had significantly shorter interbirth intervals and postpartum anovulatory intervals than did females who raised their infants until weaning.     

Parturition in gilts: duration of farrowing, birth intervals and placenta expulsion in relation to maternal, piglet and placental traits

Large White x Meishan F2 crossbred gilts (n = 57) were observed continuously during farrowing while the placentae of their offspring were labeled in order to examine the duration of farrowing and placenta expulsion in relation to maternal-, piglet- and placental traits and the duration of birth interval in relation to birth weight, birth order and placental traits. Independently from each other, litter size, gestation length and offspring directed aggression significantly (P 0.05) affected duration of farrowing. An increase in litter size was associated with an increase of duration of farrowing and an increase in gestation length was associated with a decrease of duration of farrowing. Aggressive gilts took longer to farrow, compared to non-aggressive ones. After taking into account litter size, gestation length and offspring directed aggression, placental thickness (i.e., placental weight corrected for placental surface area) was significantly (P < 0.05) related to duration of farrowing, i.e., litters with on average thicker placentae took longer to farrow. The latter effect is the result of the fact that individual placental thickness significantly (P < 0.01) affected individual birth interval, independent of birth weight. The piglet has to break its own membranes to be able to start its journey through the uterus towards the birth channel. Apparently, a thicker placenta offers more resistance and thus prolongs the process of birth. Independent of placental thickness, birth interval significantly (P < 0.01) decreased with an increase in birth order (first born to last born). The high variation of birth intervals for the last born piglets, caused a slight increase in average birth interval for the latter piglets. Litters with on average more areolae per placenta took significantly (P < 0.001) less time to be born than litters with on average less areolae per placenta (independent of total number of piglets born and other placental traits), while birth intervals within litters were not affected by this trait. Thus, these results are probably due to a gilt trait rather than a piglet trait. Since the number of areolae represent the number of uterine glands present, the gilt trait might be uterine development. Duration of placenta expulsion significantly (P < 0.01) increased with an increase of duration of farrowing. Furthermore, the first placenta was expelled significantly (P < 0.01) earlier relative to last piglet when duration of farrowing was protracted, while there was no relation of the time interval between first placenta and last piglet and the duration of placenta expulsion. In conclusion, the most important finding of this study is that placental thickness rather than birth weight appears to play an important role in the duration of birth intervals and as a result, of duration of parturition in gilts.     

Birth Intervals inM. sylvanus of Gibraltar

The length of the birth interval inMacaca sylvanus of Gibraltar was defined and one-year intervals were found to be normative. The effect of infant loss on the interbirth interval was assessed and found to have no influence. Variability in the birth interval in comparable species is noted.     

Effect of delivery season on subsequent birth interval in early 20th century in Japan

Questionnaires of birth dates of family members (13 404 families in total) were analyzed in order to examine the effects of delivery season of a baby on the subsequent birth interval. Deliveries at maternal age of 20–34 years were used. In 1921–1935, the mothers who had been delivered of a baby in August–October showed the shortest (30.62 months geometric mean) and those in February–April the longest (34.05 months) non-last intervals, with a highly significant difference among the four delivery seasons (P<0.001, Kruskal-Wallis test,n=5678). Although the intervals were abruptly prolonged just before the last birth, the above difference was also consistent in the last intervals. When seasonal distributions of last and non-last births were compared, last births tended to be concentrated in the summer half of a year (P<0.05) in 1921–1935. In 1951–1965, overall geometric mean of the interval shortened to 28.44 months, and the length of intervals did not differ appreciably according to the season of preceding delivery. Deliveries in late summer (August–October) in 1921–1935, therefore, were associated with increased risk of termination of reproduction, on one hand, but a lowered chance of prolongation of the subsequent interval, on the other hand. Possible environmental factors are discussed to explain this apparently paradoxical phenomenon.     

Birth spacing patterns in humans and apes

Comparative studies of birth interval dynamics in wild primates suffer from several problems of analysis and interpretation: (1) the data are always right-censored, (2) sample sizes are usually small, (3) the distribution of birth intervals is expected to be non-normal, (4) early offspring mortality is a confounding variable, and (5) differences in life history (e.g., presence or absence of menopause) can complicate interpretation of the results. A survival analysis designed to minimize these problems is applied to published data on wild chimpanzees and gorillas from Gombe and Virunga Parks, respectively, and to new data on wild orangutans from Tanjung Puting National Park and on a human population, the Gainj of highland Papua New Guinea. According to this analysis, the estimated median birth interval (when the offspring whose birth opens the interval does not die within the interval) is 43.3 +/- 1.0 months for the Gainj, 45.5 +/- 1.2 months for gorillas, 66.6 +/- 1.3 months for chimpanzees, and 92.6 +/- 2.4 months for orangutans.     

Determinants of birth interval in a rural Mediterranean population (La Alpujarra, Spain)

The fertility pattern, in terms of birth intervals, in a rural population not practicing contraception belonging to La Alta Alpujarra Oriental (southeast Spain) is analyzed. During the first half of the 20th century, this population experienced a considerable degree of geographical and cultural isolation. Because of this population's high variability in fertility and therefore in birth intervals, the analysis was limited to a homogenous subsample of 154 families, each with at least five pregnancies. This limitation allowed us to analyze, among and within families, effects of a set of variables on the interbirth pattern, and to avoid possible problems of pseudoreplication. Information on birth date of the mother, age at marriage, children's birth date and death date, birth order, and frequency of miscarriages was collected. Our results indicate that interbirth intervals depend on an exponential effect of maternal age, especially significant after the age of 35. This effect is probably related to the biological degenerative processes of female fertility with age. A linear increase of birth intervals with birth order within families was found as well as a reduction of intervals among families experiencing an infant death. Our sample size was insufficient to detect a possible replacement behavior in the case of infant death. High natality and mortality rates, a secular decrease of natality rates, a log-normal birth interval, and family-size distributions suggest that La Alpujarra has been a natural fertility population following a demographic transition process.     

Reproduction in wild female olive baboons

The purpose of this paper is to evaluate several factors that influence female reproduction in a large troop of wild olive baboons (Papio cynocephalus anubis) based on 4 consecutive years of demographic data. Interbirth intervals were significantly shorter for females whose infants died before their next conception than for females whose infants survived. High-ranking mothers of surviving infants had significantly shorter birth intervals than comparable low-ranking mothers, independent of maternal age. This occurred mainly because the interval from resumption of cycling to conception was significantly shorter for high-vs. low-ranking females. Dominance rank did not influence sex ratio at birth, infant survival in the first 2 years, or adult female mortality. Age was also significantly related to interbirth intervals, with older females having shorter intervals. Primiparous females had consistently longer reproductive intervals than did multiparous females, but this difference reached statistical significance only for females whose infants died before the next conception. Primiparous females also experienced significantly higher infant mortality. Data on body size and estrous cycle length indicated no differences between high- and low-ranking females. Nutritional and stress-related mechanisms that may underlie the reproductive advantages of high rank are discussed.     

Factors affecting duration of the expulsive stage of parturition and piglet birth intervals in sows with uncomplicated, spontaneous farrowings

Modern pig farming is still confronted with high perinatal piglet losses which are mainly contributed to factors associated with the progress of piglet expulsion. Therefore the aim of this study was to identify sow- and piglet factors affecting the duration of the expulsive stage of farrowing and piglet birth intervals in spontaneous farrowing sows originating from five different breeds. In total 211 litters were investigated. Breed affected duration of the expulsive stage significantly: the shortest duration was found in Large White x Meishan F2 crossbred litters and the longest duration in Dutch Landrace litters. No effect of parity on the duration of the expulsive stage was found. An increase in littersize (P<0.01), an increase in number of stillborn piglets per litter (P<0.05) and a decrease of gestation length (P<0.05, independently of littersize) all resulted in an increased duration of the expulsive stage of farrowing. A curvilinear relationship between birth interval and rank (relative position in the birth order) of the piglets was found. Besides that, piglet birth intervals increased with an increasing birth weight (P<0.001). Stillborn (P<0.01) and posteriorly presented (P<0.05) piglets were delivered after significantly longer birth intervals than liveborn and anteriorly presented piglets. The results on sow- and piglet factors affecting duration of the expulsive stage and piglet birth intervals obtained in this study contribute to an increased insight into (patho) physiological aspects of perinatal mortality in pigs.