The effect of age of mother and birth order on sex ratio at birth.
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The controversy of birth order as a risk factor for epilepsy: a study from Saudi Arabia.
PURPOSE: To evaluate the relationship between people with epilepsy and birth order. METHODS: A case-control study of 336 epileptics, 15 years and above, and their 1961 full siblings. The data was analysed by birth order and then stratified by sibship size. The 95% confidence interval (CI) for each odds ratio (OR) was obtained. ORs were calculated in the 259 probands in whom the seizure and epileptic syndrome were classifiable against their corresponding 1313 siblings. RESULTS: The OR in birth order 1 is 2.08 (1.6-2.8) on comparing probands to their unaffected siblings. In birth order 3 the OR was 1.64 (1.2-2.2) and ORs declined as birth order increased. The chi-square test for the decline was significant P < 0.05. OR in birth >2 in probands against unaffected sibs was 0.42 (0.2-0.62) in partial seizures and 0.27 (0.17-0.43) in the cryptogenic category, 86% of whom had partial seizures. CONCLUSION: In spite of some limitations in the study it seemed that there is a significant association between low birth order and the risk of epilepsy when all cases were computed together. The cryptogenic type showed the clearest association between low birth order and the likelihood of epilepsy.
Adult↗
The interaction of fraternal birth order and body size in male sexual orientation.
A late fraternal birth order has been demonstrated numerous times in homosexual men. Body size has been less studied with regard to the development of sexual orientation and has demonstrated contradictory results. In this research, the relations among fraternal birth order, body size, and sexual orientation were examined in a Canadian sample of homosexual and heterosexual men. An interaction between fraternal birth order and height was observed, with a homosexual orientation most likely to occur in men with a high number of older brothers and shorter stature. No significant interactive effects were observed for weight. The results suggest that the mechanism underlying the fraternal birth order phenomenon has an effect on physical development that lasts and is detectable into adulthood (i.e., adult stature).
Adolescent↗
Sib-size, birth order and risk of overweight in junior high school students in Japan: results of the Toyama Birth Cohort Study.
OBJECTIVE: To investigate whether there is a relationship between sib-size, birth order and the risk of overweight in junior high school students. METHOD: Sib-size, birth order, height and weight of subjects and their parents, and other lifestyle factors were obtained through a questionnaire survey conducted between June and July 2002 from 7,959 junior high students in Toyama prefecture, Japan. Logistic regression analysis was performed to examine the associations. Boys and girls were analyzed separately. RESULTS: Boys from three-child families showed a significantly lower risk of overweight than only boys (odds ratio (OR)=0.66, p=0.010), and girls from larger families have a significantly lower risk than only girls (p for trend=0.001). Compared to middle-born girls, only girls have a significantly higher risk of overweight (OR=2.22, p<0.001). The risk of overweight in boys was significantly lower with increasing number of elder sibling or sister. However, increasing of any one sibling almost had the same risk reduction effect on the risk of overweight in girls (OR ranged from 0.74 to 0.76, p<=0.001). CONCLUSION: Children without siblings are the ones most at risk for overweight, especially in girls. Birth order and sib-size are possible risk factors for the development of overweight and obesity.
Adolescent↗
Birth order and sibship size as independent risk factors for asthma, allergy, and eczema.
This study was carried out to disentangle the independent relations of birth order and sibship size with the presence of asthma, allergy and eczema. In a retrospective study, 700 families in the Netherlands were selected with index children born in 1988-90. Data were extracted from reports of health examinations at the age of 6 years of these children and their siblings. Birth order, and not sibship size, appeared to be a strong risk factor for allergy (excluding eczema). Children with higher birth order had a lower risk of allergy compared with first-borns (adjusted odds ratios: 0.43, 0.26 and 0.05 for second-, third- and fourth- or higher borns, respectively; p < 0.0001). Allergy including eczema also had a significant relation with birth order (p = 0.01). For asthma there appeared no clear relation with birth order. For asthma a non-significant relationship with sibship size (adjusted for birth order) was found (p = 0.06): first-born children in small sibships were more at risk than those in larger sibships. For allergy and eczema no such trend was observed. In conclusion, birth order is inversely related to the risk of allergy, independent of the size of the sibship.
Asthma↗
A longitudinal study of birth order, help seeking and psychopathology.
Recent studies have suggested an association between birth order and psychopathology. However, the association remains unclear due to a lack of consideration of the confounding effects of family size. At age seven years the family size and birth order of children from a large cohort of New Zealand children were examined in relation to parental help seeking for behavioural and emotional problems, and the development of DSM-III (American Psychiatric Association, 1980) disorder in pre-adolescence and adolescence. Neither the child's gender, birth order nor family size were associated with parental help seeking or the prevalence of DSM-III disorder in pre-adolescence at age 11. In adolescence at age 15, however, significantly more girls, first-borns and children from small families had DSM-III disorder, but the interactions between these factors were not significant. In particular, these associations were found with internalizing disorders. The appropriateness of further studies of birth order in relation to psychopathology is discussed.
Adolescent↗
Birth order, family size and school failure.
The effect of birth order on educational outcome in the Netherlands is reported for two major social classes, manual and non-manual. The rates of school failure (those who attended schools for the mentally retarded and who failed lower school) were studied in a population of some 200,000 young adult Dutch males born between 1944 and 1946 and whose families of origin had from one to six children. The data used were the records of the Dutch military pre-induction examination. Rates of school failure rose both with increased birth order and with increased family-size, with the exception of one-child families. School failure rates for the first, middle-and last-born were examined for the two social classes, with family size controlled. In general, school-failure rates were significantly related to birth-order position. For each family size and in both social classes, the last-born were at greater risk of school failure than were the first-born.
Adult↗
The relationship between parental age and birth order with the percentage of low birth-weight infants.
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Adolescent↗
Birth order, self-concept, and participation in dangerous sports.
We examined the effect of birth order on participation in dangerous sports, using data from a mail survey of 841 members of the United States Parachute Association drawn from the membership list of over 18,000; 52% (N = 436) responded. The questionnaires included detailed information on participation in leisure activities, background characteristics, reasons for parachuting, and self-concept; answers were obtained from an overwhelmingly middle-class, White, male, young, and college educated sample. The findings (based on descriptive statistics, correlations, and regression analysis) did not support our expectations regarding birth order and participation in dangerous sports. Several were even in opposite direction to our expectations. We did find some support for our expectation that self-efficacy would be positively related to participation in dangerous sports, but not for our expectation that self-efficacy would be related to birth order. We concluded that birth order continues to be a frustrating variable in studies of socialization.
Adolescent↗
Birth order and family size: influences on adolescents' achievement and related parenting behaviors.
The purposes of this study were to confirm birth-order and family-size differences in achievement, to confirm birth-order and family-size differences in parenting, and to examine whether parenting style and parental involvement serve as mediators of birth-order and family-size differences in achievement. Subjects were 195 ninth-grade boys and girls and their parents from urban, suburban, and rural communities in the southeast and the midwest. Questionnaire measures of adolescents' and parents' perceptions of parenting style and parental involvement were used. Birth-order and family-size differences were found in adolescents' achievement and perceptions of parenting style and parental involvement but not in parents' perceptions of parenting. However, these parenting characteristics did not mediate the differences seen in achievement by birth order and family size. Implications of these findings are discussed.
Adolescent↗
Birth order and mortality: a life-long follow-up of 14,200 boys and girls born in early 20th century Sweden.
The present study examines the sex-specific patterns of mortality by birth order in four stages of the life-course, using Poisson and logistic regression analysis. The main question posed is whether there is any continuing social effect of birth order when (a) biological factors at birth, (b) other social factors at birth and (c) socio-economic circumstances in adulthood are adjusted for. The analyses are based on the Uppsala Birth Cohort Study consisting of all 14,192 boys and girls who were born alive at the Uppsala Academic Hospital in Sweden during the period 1915-9. The results showed that all-cause mortality differed according to birth order in all of the four studied age intervals when birth year, mother's age, birth weight, gestational age, diseases of mother, diseases of the infant, social class and mother's marital status at the time of childbirth were adjusted for. The general tendency was for laterborn siblings, particularly girls women, to demonstrate a higher mortality risk than firstborn children. However, in the oldest age group (55-80 years) the previously significant association between birth order and male mortality became insignificant when adult socio-economic circumstances were controlled for. This indicates that the long-term influence of childhood birth order position on mortality is partly mediated by adult social class, education and income. The concluding section of the paper notes that laterborn children, and especially girls, were a disadvantaged group in early 20th century Sweden. Thus, for the subjects in the present study, the childhood social conditions linked to birth order position seem to have had consequences for these individuals' health and survival that extend over the whole life-course.
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Birth order and BMI in teenage girls.
The goal of this study was to investigate the relation of birth order to relative weight and prevalence of obesity in a group of 13-15 years old girls. In 1997, 1458 girls were examined. The height and weight measured by trained staff were recorded. Family size and birth order were obtained by a questionnaire. For the purpose of the present study, 776 and 250 girls coming from two- and three-child full families, respectively, were selected from the total sample on the basis of complete information. The Body Mass Index (kg/m2) was adjusted to reference US population (NCHS) by means of the LMS parameters. Prevalence of overweight and obesity was defined according to recommendation of the International Obesity Task Force. The effect of birth order on BMI was tested by one-way analysis of variance. Prevalence of obesity was tested by the means of Pearson chi-square. First and second born girls from two-sibling families did not show significant differences in average standardized BMI. Relative weight significantly differs among girls coming from three sibling families, decreasing along with the birth order. The first-born girls were 1.5 times at higher risk of obesity in comparison to later-born girls. Differences in the proportion of overweight girls among birth order groups showed a high significance within three sibling families.
Adolescent↗
Birth order, sibship size, and risk for germ-cell testicular cancer.
BACKGROUND: Several studies have reported an inverse association between birth order and testicular cancer risk, but estimates vary greatly and the biologic mechanism underlying the association is not established. METHODS: We have evaluated the effect of birth order, sibship size, and the combined effect of these 2 variables in relation to risk for testicular cancer in a large, nested case-control study. Specifically, we compared 3051 patients with germ-cell testicular cancer (diagnosed between 1958 and 1998 and identified through the Swedish Cancer Registry) with 9007 population control subjects. Using record linkage with the Multi-Generation Register and the Census, we obtained information on number, order, and sex of the subjects' siblings, parental age, and paternal socioeconomic status. RESULTS: Both birth order and sibship size had an inverse and monotonically decreasing association with testicular cancer risk after adjusting for parental age, paternal socioeconomic status, and twin status. The associations were modified by subjects' cohort of birth and were not present among those born after 1959. The odds ratio for having at least 3 siblings, compared with none, was 0.63 (95% confidence interval = 0.53-0.75) among subjects born before 1960. Stratified analyses showed that birth order and number of younger siblings had a similar inverse association with the risk for testicular cancer. CONCLUSIONS: Sibship size, and not only birth order, is associated with testicular cancer risk. This suggests a higher prevalence of parental subfertility among patients with testicular cancer.
Adult↗
Birth order and its association with the onset of chronic fatigue syndrome.
Chronic fatigue syndrome (CFS) is a medically unexplained illness that is diagnosed on the basis of a clinical case definition; so it probably is an illness with multiple causes producing the same clinical picture. One way of dealing with this heterogeneity is to stratify patients based on illness onset. We hypothesized that either the whole group of CFS patients or that group which developed CFS gradually would show a relation with birth order, while patients who developed CFS suddenly, probably due to a viral illness, would not show such a relation. We hypothesized the birth order effect in the gradual onset group because those patients have more psychological problems, and birth order effects have been shown for psychological characteristics. We compared birth order in our CFS patients to that in a comparison group derived from U.S. demographic data. We found a tendency that did not reach formal statistical significance for a birth order effect in the gradual onset group, but not in either the sudden onset or combined total group. However, the birth order effect we found was due to relatively increased rates of CFS in second-born children; prior birth order studies of personality characteristics have found such effects to be skewed toward first-born children. Thus, our data do support a birth order effect in a subset of patients with CFS. The results of this study should encourage a larger multicenter study to further explore and understand this relation.
Adult↗
Is birth order associated with adult mortality?
The objective of this study was to determine whether birth order is associated with total or cause-specific adult mortality and whether the association differed by sex, was confounded by age, number of siblings, or socioeconomic status, or was mediated by personality, education, or health behaviors. Teachers throughout California identified intellectually gifted children as part of a prospective study begun in the 1920s by Lewis Terman. Information on birth order was available on 1162 subjects (85% of cohort) who have since been followed for over 70 years. Cox proportional hazards models indicated that birth order was not associated with adult all-cause, cardiovascular, or cancer mortality. Among women, middle children were more likely than oldest children to die from causes of death other than cardiovascular disease or cancer, although the numbers in this category were small. This study did not provide evidence that birth order is associated with adult mortality in this highly intelligent, middle-class cohort.
Adolescent↗
Birth order, family size, and the risk of cancer in young and middle-aged adults.
We used the Swedish Family-Cancer Database to analyse the effects of birth order and family size on the risk of common cancers among offspring born over the period 1958-96. Some 1.38 million offspring up to age 55 years with 50.6 million person-years were included. Poisson regression analysis included age at diagnosis, birth cohort, socio-economic status and region of residence as other explanatory variables. The only significant associations were an increasing risk for breast cancer by birth order and a decreasing risk for melanoma by birth order and, particularly, by family size. When details of the women's own reproductive history were included in analysis, birth orders 5-17 showed a relative risk of 1.41. The effects on breast cancer may be mediated through increasing birth weight by birth order. For melanoma, socio-economic factors may be involved, such as limited affordability of sun tourism in large families. Testis cancer showed no significant effect and prostate cancer was excluded from analysis because of the small number of cases.
Adolescent↗
Sibship size, birth order, and atopy in 11,371 Italian young men.
BACKGROUND: Having a low number of siblings and a low birth order has been reported to be a relevant risk factor for development of atopic diseases and skin sensitization to common inhalants. Although the inverse association of atopy with sibship size has been confirmed repeatedly, the association with birth order has provided conflicting results. This possibly is due to the relatively small size of the population sample examined. OBJECTIVE: The objective of this study was to investigate the relation between sibship size, birth order, and atopy in a very large population sample, highly homogeneous for age and sex. METHODS: This was a retrospective survey of 11,371 Italian young men, 18 to 24 years old, all candidates for enrollment in the Italian Air Force. Demographic data had been collected by a standard questionnaire. Specific IgE for locally relevant airborne allergens had been tested by a multi-RAST assay (CAP-Phadiatop). RESULTS: The prevalence of atopy (defined as a high level of specific IgE against inhalants [cut-point >1.2 log RU]) was inversely related to the total number of siblings (25% in those with no siblings and 9% in those with five or more siblings), with a mean of a 3% decrease in prevalence for each added sibling. This relation persisted after adjustment for relevant variables such as father's education and rural and southern residence. An independent association between birth order and atopy was also observed because the decrease in atopy prevalence with increasing numbers of older siblings was significantly steeper than that found with the number of younger siblings (chi2 = 179, df = 1, p < 0.0001). CONCLUSIONS: In a very large and homogeneous population sample of a Mediterranean country, not only sibship size but also birth order was significantly associated with atopy. This observation further highlights the role of family structure in the development of atopy and supports the hypothesis that cross-infections acquired early in infancy or in later childhood might prevent development of atopy later in life.
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Neonatal sex and birth-order effects on behaviors of mothers and temporary caretakers during bottle-feeding.
This study examined the effects of neonatal sex and birth order on maternal caretaking patterns for pre-attachment behaviors shown by mothers and instrumental behaviors seen in both mothers and temporary caretakers. Observational category scores were obtained for mothers of 20 newborn infants and for temporary caretakers observed in a 15 min bottle-feeding situation. A repeated measures analysis of variance design was used to partition categories into caretaking classifications and to evaluate the effects of infant sex and birth order. Significant main effects for caretaker (p less than .05) were obtained: six mother-high, pre-attachment categories, and seven mother-low, instrumental behavior categories. Maternal scores sensitive to infant sex and birth order were identified from Caretaker x Sex x Birth Order interactions (p less than .05). Birth order differences affected maternal behaviors directed toward sons more substantially than those directed toward daughters. Mothers held first-born sons upright in tactual contact with the trunk, whereas daughters were held supine on the lap and exposed to frequent maternal smiling.
Adult↗