An analytic simulation model of human reproduction with demographic and biological components

Abstract This Monte Carlo model for simulating the reproductive history of a cohort of women is described in detail. The model provides for patterns of survival, sterility, formation and dissolution of sexual unions, fecundability, lactation, foetal wastage, family planning practices etc. Natality indices specific for marital status, for duration of marriage and for age, as well as analyses of birth spacing patterns are among the results that may be obtained. In the model, the experimental unit is an individual woman. The complete life history of a woman is generated and recorded before the history of the next woman is generated. The data for the whole cohort are analyzed at the end of the programme. The model includes two kinds of states into which a woman may pass, namely: (1) permanent changes of status such as death, sterility, or becoming a family planner, and (2) temporary states, each with a probability distribution of length of stay. The probabilities of the various events or changes of state may vary from age, parity, and other features of a woman's status or history. Natural fecundability at any age may also vary from woman to woman. In this programme natality patterns and specific indices such as age-specific fertility rates are produced, in a quasi-realistic fashion, by the interplay of the demographic and biological parameters postulated for any cohort. Consequently, the effect of changes in anyone factor can be studied, as well as the interaction resulting from changes in several factors. The purposes and potentials of the model are both substantive and methodological. As an illustration, a series of computer runs attempting to simulate the reproductive patterns of Indian women is presented. These results, as well as some additional ones, indicate some effects of changes in marital patterns, levels of fecundability, duration of post-partum non-susceptibility, age incidence of sterility and foetal wastage. In the final section of the paper, the advantages and possible applications of the model are discussed together with the limitations encountered to date in the efforts to apply the model.     

Contraceptive acceptance and pregnancy: a matrix approach to the analysis of competing risks

Abstract This paper represents an initial attempt to formalize the relationships among post-partum sterility, fecundability, and contraceptive acceptance in terms of absorbing Markov chains. Acceptance of contraception offered by family planning programmes is analyzed as a possible event in time for a cohort of recently delivered women as they pass through phases of temporary sterility and fecundability towards another possible pregnancy. The results of the study indicate that once a woman leaves the post-partum anovulatory stage, the probability of her becoming pregnant again is large compared to the competing rates of contraceptive acceptance currently in force. Unless highly fecund non-contracepting women are approached by family planning programmes shortly after a pregnancy has been terminated (by childbirth or abortion), they will quickly become ineligible to accept either the pill or IUD because of once again being 'currently pregnant'.     

A Model of Age-specific Fecundability

A new model of the behavioural and physiological causes of age-specific variation in marital fecundability is presented. Total fecundability is decomposed into a series of susceptibility factors (the length of ovarian cycles, the length of the fertile period within each cycle, the probability that a cycle is ovulatory, and the likelihood that an act of unprotected intercourse within the fertile period results in conception) and an exposure factor reflecting the effect of duration of marriage on coital frequency. The impact of intra-uterine mortality on effective fecundability is also modelled. Data on western women, from which standard age curves of fecundability are estimated, suggest that any decline in fecundity between ages 30 and 40 is attributable to changes, not in the ability to conceive, but in the capacity to carry a pregnancy to term. Sensitivity tests suggest that the most important potential sources of inter-population variation in fecundability are intra-uterine death and the incidence of anovulatory cycles.     

Supporting women to achieve breastfeeding to six months postpartum – The theoretical foundations of a successful program

BackgroundAlthough the benefits of breastfeeding to six months are well-established, only about half of Australian women succeed. The factors associated with successful breastfeeding are rarely translated into effective interventions. A new educational and support program, called the Milky Way program has been demonstrated to be effective in supporting women to achieve prolonged breastfeeding. In the Milky Way program, breastfeeding is considered an embodied performance which requires an engaged combination of body, mind and spirit. This paper aims to explain how the two theories that informed the program were used to better enable women's long term breastfeeding success.MethodThe theory of self-efficacy is first described as a way to develop women's cognitive processes to organise and execute the course of actions to breastfeed for a longer period of time. Birth territory theory is then presented. This theory discusses women as embodied selves; an essential concept for breastfeeding success. Birth territory theory also describes the effects of the holistic environment on the woman and explores the effects of power that is used in the environment. This power can be used integratively to strengthen the woman's breastfeeding confidence and success or, disintergratively which reduces her confidence and undermines her success.ConclusionStrategies based on self-efficacy theory are helpful, but are not sufficient to promote breastfeeding to six months. Health educators also need to foster the woman's connection to, and trust in, her body and her baby's body to breastfeed spontaneously. Being aware of environmental impacts on how the woman and baby breastfeed; and using one's own power integratively is crucial to women being able to achieve prolonged breastfeeding.     

Uncovering the impact of the HIV epidemic on fertility in Sub-Saharan Africa: the case of Malawi

We evaluate the impact of the HIV/AIDS epidemic on the reproductive behaviour for all women in Malawi, HIV-negative and HIV-positive alike, allowing for heterogeneous response depending on age and prior number of births. HIV/AIDS increases the probability that a young woman gives birth to her first child, while it decreases the probability to give birth of older women and of women who have already given birth. The resulting change in the distribution of fertility across age groups is likely to be more demographically and economically important than changes in the total number of children a woman gives birth to.     

Fecundability and its relation to age in a sample of Taiwanese women

Abstract In this paper reliable estimates of mean fecundability at marriage for a sample of heterogeneous Taiwanese women are obtained by using a set of data collected retrospectively. The effects of 'truncation bias' and 'memory bias' are estimated by studying the relationships between mean fecundability and the duration of marriage. Then the variations in fecundabilities by age at marriage are studied. The data are taken from an intensive fertility survey of married women between the ages of 20 and 39 conducted in Taichung city of Taiwan towards the end of 1962 prior to a year-long family planning action programme. Fecundability, the probability of conception in the absence of contraception, is estimated by using a Type I geometric model and is estimated from the observed distribution of first pregnancy intervals-the period between the onset of marriage and the beginning of first conception. The estimated fecundability level relatively free from truncation and memory bias is 195±3 per 1.000 women. The fecundability level increases with wife's age at marriage (up to 25) independently of its association with the duration of marriage.     

Hutterite fecundability by age and parity: Strategies for frailty modeling of event histories

Effective fecundability declines with age and parity. Furthermore, women differ in their effective fecundability: some women have persistently low or high monthly chances of live-birth conception. Estimates are presented concerning the magnitude of these effects in a natural-fertility population: 406 Hutterite women in North America who had 3,206 births, largely in the 1940s and 1950s. The estimates are based on models that incorporate the effects of persistent heterogeneity and that use the full information provided by multiple-spell duration data. In addition, hazards rather than probabilities are modeled, piecewise linear hazard functions are used, and age and parity effects are decomposed systematically. These methods permit the development of more elaborate models of changing fecundability and of heterogeneity in postpartum amenorrhea.     

A model for estimating fecundability of the currently married woman from the data on her susceptibility status—A cohort approach

A probability model to estimate fecundability of a married woman has been proposed under some mild assumptions. It utilises the knowledge on the susceptibility status of the married women (including menstruation, menopause, pregnancy and amenorrhea) and therefore sets another approach for estimating fecundability. In addition, it is capable of predicting the parity, proportion of foetal losses, fecundability and incidence of secondary sterility. The problem of finding out the consistent estimates of the parameters in the distribution is discussed in section 4. For illustra-tion, the model is applied to a set of simulated data after simplifying many assumptions of the model     

Interpersonal communication and the diffusion of family planning in West Malaysia

Using data from a 1966–1967 probability sample of West Malaysian married women 15–44 years of age, this paper analyzes the characteristics of women who were active in diffusing information about family planning. The woman’s age and her parity, her educational attainment, her race, her present residence (urban-rural), and whether or not she wanted more children were significantly related to opinion leadership in bivariate tables. However, these relationships appeared to be substantial mainly because these social and demographic characteristics were highly related to whether the woman participated in discussions about family planning with other women. Among women who did participate in such discussions, the social and demographic variables were not substantially related to opinion leadership. In fact, the critical variables for opinion leadership appeared to be participation in the discussions, greater knowledge of family planning, and a higher level of family planning use. An attempt is also made to assess the effect of interpersonal communication on the adoption of family planning among women in the sample.     

Effects of various factors on selection for family planning status and natural fecundability: A simulation study

The effect of various factors on selection for family planning status and for natural fecund ability is studied in a simulation that incorporates a beta distribution of fecundability among women. The mean fecundabilities of current spacers, current limiters, current nonusers, and pregnant women are compared. These ratios are influenced by duration of marriage and by desired number of children. Effects of different levels of contraception are measured. Another strategy, spacing the last two wanted births, is also studied. It is found that breast-feeding status has little effect on fecundability selection. The women usually found to have greatest fecundability are not those recently pregnant at durations of marriage five and ten years, unless they wanted fewer than two children, but rather those who are using contraception to limit the number of children.     

Socio-economic correlates of fecundability in a sample of taiwanese women

Estimates of fecundability (monthly probability of conception) in the absence of contraception are derived from the frequency distribution of conceptive delays immediately following marriage, reported by 2,443 married women aged 20 to 39 included in the Taichung (Taiwan) Intensive Fertility Survey of 1962. Average fecundability of women is positively associated with their socio-economic status. These differentials are not accounted for by differences among socio-economic groups with respect to memory and truncation biases (associated with the marriage duration), wife’s age at marriage, or unreported premarital conceptions. A Multiple Classification Analysis suggests that among the socio-economic characteristics, husband’s education, rural background, and modern family type are the more important predictors of fecundability. The importance of genetic factors as opposed to cultural factors in producing these socio-economic differences in fecundability can not be evaluated systematically. Moreover, the relation of a couple’s privacy, their attitude toward family building, and patterns of mate selection to their socioeconomic status would have to be taken into account before the differences in fecundability could be attributed to factors such as nutrition, health, or infections which might directly influence their physiological ability to conceive.     

Factors that influence women’s decision on infant feeding: An integrative review

BackgroundMany women stop breastfeeding earlier than what they intended prior to birth. Although there are many studies that focus on the factors that influence women’s antenatal breastfeeding decisions, the factors that influence women’s decisions during the continuum of antenatal and postnatal period are less known.AimTo understand and synthesise the contemporary factors that influence women’s decisions on infant feeding from the antenatal period and across the breastfeeding continuum.MethodFive online databases (CINAHL, Medline, PubMed, Scopus and Web of Science) were searched. We included original search articles that were published since 2015 to August 2021 and were available in English. The framework of Whittemore and Knafl was used to guide this integrative literature review. Out of the 872 articles identified, 14 studies met the inclusion criteria of our study. We used theory of birth territory and midwifery guardianship to synthesise the interactions between the themes.FindingsFive main themes were identified: (a) Women’s own views, (b) Family and friend’s preferences and advice, (c) Health professional’s preference, advice and practice, (d) Sociocultural norms, and (e) Media representation. The interaction between the themes was explained based on women’s intrinsic and extrinsic power outlined in the birth territory and midwifery guardianship theory.ConclusionThe factors that influence women’s decisions towards infant feeding methods are complex and multi-dimensional. Promoting and supporting women towards breastfeeding need to focus on the factors that are tailored for a woman within her social network where she can feel safe about her breastfeeding decisions.     

The determinants of effective fecundability based on the first birth interval

There are substantial differences in fecundability among nine developing countries in different parts of the world. In addition, within countries, later age at marriage has a clear, positive, nonlinear effect on fecundability. Women with higher education and those with more educated husbands have higher fecundability. Urban residents have higher fecundability than rural. The higher fecundability of more recent cohorts is the most consistent observation. Since those variables most frequently shown to have inverse relationships to fertility show direct relationships to fecundability within populations, the role of fecundability as a proximate variable in models of the determinants of fertility requires further specification.     

Intensive Parenting: Fertility and Breastfeeding Duration in the United States

Using 30 years of longitudinal data from a nationally representative cohort of women, we study the association between breastfeeding duration and completed fertility, fertility expectations, and birth spacing. We find that women who breastfeed their first child for five months or longer are a distinct group. They have more children overall and higher odds of having three or more children rather than two, compared with women who breastfeed for shorter durations or not at all. Expected fertility is associated with initiating breastfeeding but not with how long mothers breastfeed. Thus, women who breastfeed longer do not differ significantly from other breastfeeding women in their early fertility expectations. Rather, across the life course, these women achieve and even exceed their earlier fertility expectations. Women who breastfeed for shorter durations (1–21 weeks) are more likely to fall short of their expected fertility than to achieve or exceed their expectations, and they are significantly less likely than women who breastfeed for longer durations (≥22 weeks) to exceed their expected fertility. In contrast, women who breastfeed longer are as likely to exceed as to achieve their earlier expectations, and the difference between their probability of falling short versus exceeding their fertility expectations is relatively small and at the boundary of statistical significance (p = .096). These differences in fertility are not explained by differences in personal and family resources, including family income or labor market attachment. Our findings suggest that breastfeeding duration may serve as a proxy for identifying a distinct approach to parenting. Women who breastfeed longer have reproductive patterns quite different than their socioeconomic position would predict. They both have more children and invest more time in those children.     

The effects of children on divorce and re-marriage: a multivariate analysis of life table probabilities

Summary Using proportional hazards models and multiple decrement life tables to analyse data from the 1973 National Survey of Family Growth, this study tests the hypotheses that, net of the effects of such factors as age at separation or divorce, the probabilities of divorce after separation and of re-marriage after divorce would be lower for women with larger numbers of children or younger children, and that these transitions would take longer than for women with fewer or older children or women who were childless; and that there would be an interaction between number of children and age of youngest child. Results included: (1) the probability that mothers of two or more children would divorce after separation was significantly lower than for childless women, or those with only one child; (2) among whites, mothers of three or more children were at a significant disadvantage regarding their chances of re-marriage, whereas the probability that a black mother of three or more children would re-marry was no smaller than that of a woman with fewer or no children; (3) among whites, the presence of a youngest child aged between two and five years at separation decreased the probability of divorce after separation; (4) there was no interaction effect between number and age of children; and (5) in each category of family size and age of youngest child, the probability that a black woman would divorce after separation or re-marry after divorce was lower than for white women. The results have important implications for the study of divorce and re-marriage, and for understanding of problems of single-parent families.     

A probability model applicable to the study of inter-live birth intervals and random segments of the same

Abstract This paper deals with an analytical study of two types of birth intervals, viz. 'closed intervals' and 'open intervals' through the application of simple probability theory. The 'closed interval' stands for the time interval between two successive live births of a woman, and the 'open interval' denotes the interval between the date of last live birth and the date of survey for a married woman in the reproductive age group surveyed at a point of time. The study considers the 'closed interval' as the sum of independent random variables, each representing a particular component like post-partum amenorrhea, waiting time in the susceptible state, etc. Approximations to the patterns of distributions of these component random variables are made from the available data collected in fertility surveys at Gandhigram. The 'open interval' for any parity is studied separately for two different (mutually exclusive) categories of women, viz. those who have at least one more live birth at some time or other during their reproductive period and those who cease childbearing. In the first case the 'open interval' is considered as a random segment or partition of the corresponding 'closed interval'; in the second as a random segment of the interval between the date of birth of the last child and date at which the woman attains 45 years of age. The mean and variance of the 'open interval' is obtained separately in each case, and the moments of the 'open interval' distribution for women chosen at random from the population are obtained as an appropriate mixture of the two types.     

A non‐linear model of fecundability,postpartum amenorrhea,and sterility*

This paper proposes a convolution model of fecundability, controling for the effects of postpartum amenorrhea and unobserved heterogeneity in fecundability. Simulation analysis was used to assess the validity and reliability of estimates derived from the model. Analysis showed that the model captured the mean and standard deviation of age at the onset of sterility in simulated populations where sterility followed either a Gompertz, a gamma, or a lognormal distribution. The model performed well when sterility was specified by either a lognormal or a gamma distribution. The model also accurately estimated fecundability and postpartum amenorrhea. Next, the model was found to fit data from 17th and 18th century French Canadian birth histories. In this French Canadian sample the mean age at sterility was found to be 46.3 years using a gamma model. The decline in fecundability was almost linear after age 30. Thus, fecundability at age 40 had declined to about one‐third of that observed at age 30. Variability in individual fecundability was quite high. For example, women with fecundability one standard deviation above the mean had about 2.3 times as high fecundability as women one standard deviation below the mean.     

“It Makes My Skin Crawl”: Women’s experience of breastfeeding aversion response (BAR)

ProblemSome women who intend to breastfeed experience a breastfeeding aversion response (BAR) while breastfeeding.BackgroundLittle is known about the experience of those who have feelings of aversion while breastfeeding.AimThis study aimed to investigate the experiences of women who have an aversion response to breastfeeding while their infant is latched at the breast. This is the first study that aims to understand this breastfeeding aversion response (BAR) as described by women who experience this phenomenon.MethodsInterpretative phenomenological analysis (IPA) was used to conduct and analyse ten semi-structured in-depth interviews with women who self-identified as experiencing BAR.FindingsFour overarching themes were identified: (1) Involuntary, strong sensations of aversion in response to the act of breastfeeding, (2) Internal conflict and effects on maternal identity, (3) The connection between BAR and relationships with others, and (4) Reflections on coping with BAR and building resilience.DiscussionSome women who intend to breastfeed can experience BAR, and this negative sensation conflicts with their desire to breastfeed. BAR can impact on maternal wellbeing. Those who experience BAR may benefit from person-centred support that directly addresses the challenges associated with BAR to achieve their personal breastfeeding goals.ConclusionThe experience of BAR is unexpected and difficult for mothers. If support is not available, BAR can have detrimental effects on maternal identity, mother–child bonds, and intimate family relationships.     

Findings and implications of a correlation analysis of the closed and the open birth intervals

A correlation analysis of data on four fertility variables viz. closed birth interval, open birth interval, age and parity, collected in a survey of about 2,000 married women in the reproductive ages in rural India, is carried out in order to study the interrelationships among these variables. Two hypotheses are formulated governing the relationship of the closed and open birth intervals with the fecundability distribution of fertile women, and Parity Progression Ratios which are largely influenced by the proportion of women becoming sterile after each parity. The data lend support to the hypothesis that while the closed intervals are influenced mainly by the distribution of fecundability of women of non-zero fecundability, the open birth intervals are influenced mainly by Parity Progression Ratios or the proportion of women becoming secondarily sterile after each parity. The analysis suggests that we can use the mean open intervals of women classified by parity as indices of fertility, and such an index is comparable to the index of average age of women of given parity. In areas where it is difficult to ascertain the correct age of women this might be of practical value.     

The seasonality of conception

Individual data on menstrual cycles of noncontracepting women living in Western countries were used in order to verify whether the biological seasonality of conception persists after sexual behavior is controlled for. Episodes of intercourse were recorded daily, and the time of ovulation was detected by a marker We find that the seasonality of conception changes with woman's age and frequency of episodes of sexual intercourse. In particular; for women aged 27-31 having only one act of intercourse during the six most fertile days of the menstrual cycle, the seasonality of fecundability is stronger In this age group in the Northern Hemisphere, if seasonality of acts of sexual intercourse is controlled, the monthly distribution of probability of conception is bimodal, with two maxima (September and January) and two minima (December and March). When unobserved characteristics of the couples are considered, this seasonal pattern of conception persists.