Perinatal mortality by birth order within cohorts based on sibship size.

Cross-sectional surveys of perinatal mortality show a U-shaped curve when plotted against parity, implying that fourth and subsequent babies are at increased risk. Our study of a large, population-based longitudinal data set shows that this result is an artefact and that perinatal mortality falls with increasing parity. Within cohorts of mothers based on attained sibship size the perinatal mortality decreases with increasing parity and increases with sibship size. These associations, which are not noticeably affected by maternal age, ssem in part to operate through an association between parity, sibship size, and birth weight. This analysis shows the importance of using longitudinal data in analysing such relations.     

Birth order and health status in a British national sample.

Researchers analyzed data from the National Child Development Study--a cohort of every child born in England, Scotland, and Wales during the 1st week of March 1953 with follow up studies in 1965, 1969, 1973, and 1980-1981 to examine the relationship between health status and birth order and whether children with low birth orders were less likely to experience illness than those with older siblings. 1st born children tended to have received the needed number of immunizations, but children of higher birth order did not tend to have received them. Further they were more likely to have attended infant welfare and toddler clinics for health care than children of higher birth order. The only childhood contagious disease which demonstrated a social class effect was pertussis. It tended to afflict children from nonmanual homes regardless of birth order. Absences from school lasting between 1 week-1 month of 1st born children were less frequent than for other children. The leading reasons for 1st, 3rd, and later born 11 year old children who experienced such long absences included infectious diseases; bronchitis; ear, nose, and throat complaints; pneumonia; tonsillitis, or viral influenza. After age 15, 1st and 2nd born children were less likely to be absent and, if absent, they tended to only miss 1 week of school. Significantly more 3rd and 4th born children were absent from school for 1 week-3 months. 1st and 2nd born children from more affluent families tended to have early childhood asthma. In conclusion, the health experiences of the later birth orders were different than those of the 1st born. This did not mean, however, that later birth order children were in poorer health than 1st born children.     

Birth order and relationships

Previous studies (Salmon 1999; Salmon and Daly 1998) have found that sex and birth order are strong predictors of familial sentiments. Middleborns tend to be less family-oriented than firstborns or lastborns, while sex differences seem to focus on the utility of kin in certain domains. If this is a reflection of middleborns receiving a lesser degree of support from kin (particularly in terms of parental investment), are middleborns turning to reciprocal alliances outside the family, becoming friendship specialists? Are there comparable birth order differences with respect to mating strategies? In this study, the impact of birth order on attitudes toward family, friends, and mating were examined. Two hundred and forty-five undergraduates completed a questionnaire relating to their attitudes toward friends and family as well as some aspects of mating behavior. Birth order did have a significant impact in several areas. Middleborns expressed more positive views toward friends and less positive opinions of family in general. They were less inclined to help family in need than firstborns or lastborns. Mating strategies also appeared to be influenced by birth order, most notably in the area of infidelity, with middleborns being the least likely birth order to cheat on a sexual partner.     

Birth order and male androphilia in Samoan fa'afafine

The manner in which male androphilia is publicly expressed varies cross-culturally. As such, it is unclear whether distinct or common underlying causal processes characterize male androphilia in different cultures. Establishing the existence of cross-cultural universals in male androphilia is one means of ascertaining whether common biological bases underlie this phenomenon despite its culturally distinct forms. The evidence that the number of older biological brothers increases the odds of androphilia in later-born males has been well documented for Western samples (i.e. the fraternal birth order effect); but there is little evidence for this effect in non-Western samples. Here, we compare the birth order of androphilic males (i.e. fa'afafine) and gynephilic males from the politically autonomous Polynesian nation of Independent Samoa. Results indicate that relative to gynephilic males, fa'afafine tend to have more siblings and are generally later born when birth order is quantified using Slater, fraternal and sororal indices. More specifically, fa'afafine tend to have a greater number of older brothers, older sisters and younger brothers. We discuss the observed effects in relation to the differing reproductive patterns exhibited by the mothers of fa'afafine and gynephilic males, and to existing social and biological theories for sexual orientation.     

Distribution of sibship size in families manifesting a genetically determined disorder.

The effect on sibship size distribution of the birth of a child with a genetical defect is considered for several different conditions. Family size continues to be over-dispersed in such cases, rather than showing any sign of reduced variation, though theoretical expectations about the correlation between numbers of normal and affected children are not well-supported by the data.     

Birth weight,adult body size,and risk of colorectal cancer

BackgroundEvidence suggests that birth weight may be associated with colorectal cancer (CRC) risk later in life. Whether the association is mediated by adult body size remains unexamined.MethodCox proportional hazards models (Hazard Ratio (HR) and 95 % Confidence Intervals (CI)) were used to evaluate the association between self-reported birth weight (<6 lbs, 6-<8 lbs, ≥8 lbs) and CRC risk among 70,397 postmenopausal women from the Women’s Health Initiative. Further, we assessed whether this association was mediated by adult body size using multiple mediation analyses.ResultsCompared with birth weights of 6-< 8 lbs, birth weight ≥ 8 lbs was associated with higher CRC risk in postmenopausal women (HR = 1.31, 95 % CI 1.16–1.48). This association was significantly mediated by adult height (proportion mediated =11.4 %), weight (11.2 %), waist circumference (10.9 %), and body mass index at baseline (4.0 %). The joint effect of adult height and weight explained 21.6 % of this positive association.ConclusionOur data support the hypothesis that the intrauterine environment and fetal development may be related to the risk of developing CRC later in life. While adult body size partially explains this association, further investigation is required to identify other factors that mediate the link between birth weight and CRC.     

Birth outcomes in the Inuit-inhabited areas of Canada

Background

Information on health disparities between Aboriginal and non-Aboriginal populations is essential for developing public health programs aimed at reducing such disparities. The lack of data on disparities in birth outcomes between Inuit and non-Inuit populations in Canada prompted us to compare birth outcomes in Inuit-inhabited areas with those in the rest of the country and in other rural and northern areas of Canada.

Methods

We conducted a cohort study of all births in Canada during 1990–2000 using linked vital data. We identified 13 642 births to residents of Inuit-inhabited areas and 4 054 489 births to residents of all other areas. The primary outcome measures were preterm birth, stillbirth and infant death.

Results

Compared with the rest of Canada, Inuit-inhabited areas had substantially higher rates of preterm birth (risk ratio [RR] 1.45, 95% confidence interval [CI] 1.38–1.52), stillbirth (RR 1.68, 95% CI 1.38–2.04) and infant death (RR 3.61, 95% CI 3.17–4.12). The risk ratios and absolute differences in risk for these outcomes changed little over time. Excess mortality was observed for all major causes of infant death, including congenital anomalies (RR 1.64), immaturity-related conditions (RR 2.96), asphyxia (RR 2.43), sudden infant death syndrome (RR 7.15), infection (RR 8.32) and external causes (RR 7.30). Maternal characteristics accounted for only a small part of the risk disparities. Substantial risk ratios for preterm birth, stillbirth and infant death remained when the comparisons were restricted to other rural or northern areas of Canada.

Interpretation

The Inuit-inhabited areas had much higher rates of preterm birth, stillbirth and infant death compared with the rest of Canada and with other rural and northern areas. There is an urgent need for more effective interventions to improve maternal and infant health in Inuit-inhabited areas.Birth outcomes are worse in Aboriginal than in non-Aboriginal populations in many developed countries, including the United States, Australia and Canada.^1–18 Inuit are the smallest Aboriginal group in Canada, with a population of about 45 000.¹⁹ Some regional and community studies have shown that Inuit experience the highest rates of infant mortality in Canada.^16–18 However, data are lacking at the national level on birth outcomes among Inuit owing to the absence of Aboriginal identifiers on birth registration forms in most provinces.In Canada, over 80% of all Inuit reside in one of four vast, sparsely populated regions: the Inuvialuit region of the Northwest Territories, Nunavut, Nunavik (northern Quebec) and Nunatsiavut (northern coast of Labrador) (Figure 1). Taken together, 80% of the population in those four regions is Inuit,²⁰ and 90% of the births are to Inuit women according to 2006 census data. This creates an opportunity to examine birth outcomes according to maternal place of residence in any of the four Inuit-inhabited areas of Canada. We conducted this study to describe birth outcomes in those areas compared with outcomes in the rest of country and in other rural and northern areas of Canada.Open in a separate windowFigure 1Inuit-inhabited communities in the Inuvialuit (dots), Nunavut (triangles), Nunavik (squares) and Nunatsiavut (stars) regions of Canada. Source: Statistics Canada population data. Base map © 2002 Government of Canada with permission from Natural Resources Canada.     

Body size, body shape, and long bone strength in modern humans

To identify behaviorally significant differences in bone structure it is first necessary to control for the effects of body size and body shape. Here the scaling of cross-sectional geometric properties of long bone diaphyses with different "size" measures (bone length, body mass, and the product of bone length and body mass) are compared in two modern human populations with very different body proportions: Pecos Pueblo Amerindians and East Africans. All five major long bones (excluding the fibula) were examined. Mechanical predictions are that cortical area (axial strength) should scale with body mass, while section modulus (bending/torsional strength) should scale with the product of body mass and moment arm length. These predictions are borne out for section moduli, when moment arm length is taken to be proportional to bone length, except in the proximal femoral diaphysis, where moment arm length is proportional to mediolateral body breadth (as would be expected given the predominance of M-L bending loads in this region). Mechanical scaling of long bone bending/torsional strength is similar in the upper and lower limbs despite the fact that the upper limb is not weight-bearing. Results for cortical area are more variable, possibly due to a less direct dependence on mechanical factors. Use of unadjusted bone length alone as a "size" measure produces misleading results when body shape varies significantly, as is the case between many modern and fossil hominid samples. In such cases a correction factor for body shape should be incorporated into any "size" standardization.     

An evolutionary account of status, power, and career in modern societies

We hypothesize that in modern societies the striving for high positions in the hierarchy of organizations is equivalent to the striving for status and power in historical and traditional societies. Analyzing a sample of 4,491 US men and 5,326 US women, we find that holding a supervisory position or being in charge of hiring and firing is positively associated with offspring count in men but not in women. The positive effect in men is attributable mainly to the higher proportion of childlessness among men in non-supervisory positions and those without the power to hire and fire. This effect is in accordance with the positive relationship between other status indicators and reproductive success found in men from traditional, historical, and modern societies. In women, we further find a curvilinear relationship between income percentile and offspring number by analyzing US census data, indicating that women may strive for resources associated with advancement rather than for status per se.     

Birth order and fluctuating asymmetry: a first look

We investigated the hypothesis that maternal immunoreactivity to male-specific features of the foetus can increase developmental instability. We predicted that the participants' number of older brothers would be positively related to the fluctuating asymmetry of ten bilateral morphological traits. The participants were 40 adult male psychiatric patients and 31 adult male hospital employees. Consistent with the hypothesis, the participants' number of older brothers--but not number of older sisters, younger brothers or younger sisters--was positively associated with fluctuating asymmetry. The patients had significantly larger fluctuating asymmetry scores and tended to have more older brothers than the employees, but the positive relationship between the number of older brothers and fluctuating asymmetry was observed in both groups.     

Birth order and oral clefts: a meta analysis

BACKGROUND: There is evidence that late birth order is associated with some complex disorders. For orofacial clefts there is no consensus as to whether increased birth order is associated or not. A meta-analysis of published data on cleft lip or cleft palate (CL/P and CP) was carried out to ascertain whether there is an increased risk for children of high birth order to have an oral cleft. METHODS: All data available with information regarding the frequency of live births and CL/P and CP cases by birth order (1, 2, 3, and 4 or more) were included in the analysis, and the birth order category "1" was considered to be with no risk (OR = 1.0). RESULTS: Children with higher birth order are more likely to have CL/P and CP with odds ratios increasing with birth order to a peak of 3.0 in children birth order "4 or more." Results are not different when isolated and syndromic cases are combined. CONCLUSIONS: CL/P and CP occurrence is correlated with increasing birth order. Further studies, taking into consideration sample size and factors such as income status, race, paternal age, vitamin intake, and social habits, should be done to determine conclusively the association between birth order and oral clefts.