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Birth order and risk of testicular cancer.

To explore the etiology of testicular cancer, cases of testicular cancer were identified among members of a cohort of Danish boys born between 1941 and 1957 (inclusive), who had attended schools in Copenhagen and Gentofte and whose school health records were contained in an archive under the supervision of the Danish Cancer Registry. One hundred and eighty-three cases of testicular cancer diagnosed before 31 December 1984 were identified; 366 controls, matched to cases by sex and age, were selected from the same cohort. Information on potential risk factors and confounders was obtained from two sources: school health records and midwife protocols, both of which were recorded prior to the diagnosis of testicular cancer in cases. Relative risks (RR) approximated by the odds ratios were calculated and, in logistic regression analyses, adjustments were done for known or suspected confounders. A decreasing risk of testicular cancer with increasing birth order was observed (P = 0.020). Compared with being firstborn, being number four or more in birth order was associated with a significantly decreased RR for all testicular cancers (RR = 0.3, 95 percent confidence interval [CI] = 0.3-0.8) and testicular seminoma (RR = 0.1, CI = 0.02-0.9). No association was observed between high social class and the risk of testicular cancer (RR = 1.4, CI = 0.8-2.3); neither was age at which the study subjects had mumps or measles related to risk of testicular cancer. No cases of mumps orchitis were observed before or during school years. A slightly increased RR for testicular cancer among boys from small families could be explained by the association between family size and birth order.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

Birth order, atopy, and risk of non-Hodgkin lymphoma.

BACKGROUND: Immune deficiency is a strong risk factor for non-Hodgkin lymphoma (NHL), but whether or not other forms of immune dysregulation are associated with NHL risk is unknown. We investigated associations between atopy, which is associated with a Th2-dominant immune response, and NHL risk. Because late birth order and childhood crowding are inversely associated with atopy, we also investigated their associations with NHL risk. METHODS: We carried out a population-based case-control study among adults aged 20-74 years in New South Wales and the Australian Capital Territory, Australia. NHL patients without clinically apparent immune deficiency (N = 704) were selected from a cancer registry, and control subjects (N = 694) were randomly selected from state electoral rolls and frequency-matched to case patients by age, sex, and area of residence. Birth order, childhood crowding, and history of atopic conditions (hay fever, asthma, eczema, and specific allergies) were assessed by questionnaire and interview. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated from logistic regression models that included the matching variables as covariates. RESULTS: The odds ratios for developing NHL were 0.52 (95% CI = 0.32 to 0.84) for only children, 0.55 (95% CI = 0.40 to 0.75) for first-born children, 0.70 (95% CI = 0.51 to 0.96) for second-born children, and 0.81 (0.57 to 1.14) for third-born children (all compared with fourth- or later-born children) (P(trend)<.001). Indicators of crowding in later childhood, such as sharing a bed or bedroom, were not associated with NHL risk. A history of atopic conditions was associated with a reduced risk of NHL; this reduction was statistically significant for hay fever (OR = 0.65, 95% CI = 0.52 to 0.82) and food allergies (OR = 0.29, 95% CI = 0.20 to 0.42). CONCLUSIONS: Early birth order and its immunologic consequence, a Th2-dominated immune response, as reflected by a history of atopic disease, are associated with a reduced risk of NHL.

Adult↗

Does the sibling effect have its origin in utero? Investigating birth order, cord blood immunoglobulin E concentration, and allergic sensitization at age 4 years.

There is a great body of evidence that siblings have a protective effect against atopic manifestations such as hay fever, atopic eczema, allergic sensitization, or asthma. Factors that may explain this association remain largely unknown. One hypothesis is that siblings promote early infections in childhood, and repeated infections protect against atopic disorders. Another hypothesis, the potential in utero programming, has been neglected. The authors investigated if cord blood immunoglobulin E (IgE) is dependent upon birth order and if both are associated with an increased incidence of allergic sensitization (skin prick test) at the age of 4 years in a cohort of 981 newborns recruited between January 1989 and February 1990 on the Isle of Wight, England. The authors found that IgE is reduced with increasing birth order (first child: odds ratio (OR) = 1; second child: OR = 0.78, 95% confidence interval (CI): 0.57, 1.05; third child: OR = 0.59, 95% CI: 0.41, 0.83). Cord IgE, but not birth order, is a significant predictor of skin prick test positivity at age 4 (IgE below detection limit: OR = 1; IgE of 0.2-<0.5 kilounits/liter: OR = 1.11, 95% CI: 0.73, 1.68; IgE of >or=0.5 kilounits/liter: OR = 2.63, 95% CI: 1.62, 4.29). The findings suggest that cord IgE is reduced in pregnancies with higher order, indicating that the sibling effect may have its origin in utero.

Birth Order↗

The secondary sex ratio, paternal age, maternal age and birth order in Japan.

The simultaneous effects of several variables on the secondary sex ratio have been examined using data from over 3.7 million births which occurred in Japan during 1975--6. A weak and negative association between sex ratio and birth order was observed but it was not significant in the statistical sense. A negative effect of paternal age--birth order interaction was obtained when maternal age was controlled. The quadratic model is much more powerful than the linear model in explaining the sex ratio variability.

Adolescent↗

Family size, birth order, and parental age among male paraphilics and sex offenders.

A sample of 1823 male paraphilics, sex offenders, and non-sex offender controls were compared on family size, birth order, and parents' ages at the time of the probands' births. Sample data were also compared to population data from Statistics Canada. The men in all groups were from larger than average Canadian families and they tended to be later born. Paraphilics and sex offenders had even larger families than offender controls. Their parents tended to be older at their birth with 34.2% of mothers and 51.3% of fathers over 30 years of age, but there were no statistically significant subgroup differences. There were also significantly more multiparous teenage mothers than expected and more paraphilics' fathers who were younger than the mothers, both factors associated in the literature with increased risk of perinatal complications and abnormalities. The confounding influences of parental age, birth order, and family size were examined and indicated the need for large samples and multivariate analysis in evaluating the role of family variables associated with paraphilics and sex offenders.

Adult↗

Birth order and intellectual development: the confluence model in the light of cross-cultural evidence.

For Israeli eighth-grade students of Asian-African origin, achievement decreases as a function of birth order in small families and increases as a function of birth order in large families. This finding cannot be accounted for by differences in developmental rate or size of birth intervals. It can be accounted for by considering the effect of external influences, such as schooling, on intellectual development.

Achievement↗

Effects of gender, birth order, and other correlates on childhood mortality in China.

Using data from the 1988 Two-Per-Thousand Survey of Fertility and Birth Control, this paper examines the effects of gender, birth order, and other correlates of childhood mortality in China. Controlling for family-level factors, childhood mortality is found to be associated with the child's gender and birth order. Among firstborn children the difference between male and female childhood mortality is not statistically significant, but among others, female children between ages 1 and 5 experience higher mortality than male children. Childhood mortality is slightly higher for children who have older brothers only than for those who have older sisters only, and it is highest for those who have both older brothers and sisters. Other factors affecting childhood mortality in China include mortality of older siblings, birth interval, urban/rural residence, mother's level of education, and mother's occupation. All interactive effects between gender and family-level characteristics are found to be statistically insignificant.

Birth Intervals↗

Effect of birth order on neonatal morbidity and mortality among very low birthweight twins: a population based study.

OBJECTIVE: To study the effect of birth order on the risk for respiratory distress syndrome (RDS), chronic lung disease (CLD), adverse neurological findings, and death in very low birthweight (VLBW; < 1500 g) twins. METHODS: A population based study of VLBW infants from the Israel National VLBW Infant Database. The sample included all complete sets of VLBW twin pairs admitted to all 28 neonatal intensive care units between 1995 and 1999. Outcome variables were compared by birth order and stratified by mode of delivery and gestational age, using General Estimating Equation models, with results expressed as odds ratio (OR) with 95% confidence interval (CI). RESULTS: Second twins were at increased risk for RDS (OR 1.51, 95% CI 1.29 to 1.76), CLD (OR 1.36, 95% CI 1.11 to 1.66), and death (OR 1.24, 95% CI 1.02 to 1.51) but not for adverse neurological findings (OR 1.20, 95% CI 0.91 to 1.60). Mode of delivery did not significantly influence outcome. The odds ratio for RDS in the second twin was inversely related to gestational age, and the increased risk for RDS and CLD was found in both vaginal and caesarean deliveries. CONCLUSIONS: VLBW second twins are at increased risk for acute and chronic lung disease and neonatal mortality, irrespective of mode of delivery.

Birth Order↗

Effect of birth order and perceived stress on social schemata.

This experiment used the Felt Figure Technique developed by Kuethe in an attempt to investigate the relationship between birth order and the use of specific social schemata. Seven object sets were used, three two-figure sets and four three-figure sets. The results indicated that for the two-figure sets, firstborn individuals placed the figures closer together than laterborn individuals. For the three-figure sets, firstborn individuals under stress placed the figures closer together. The three-figure sets were also ordered in terms of the number of human figures in the object set. The results suggest that there is a measurable relationship between birth order and social schemata used by an individual.

Birth Order↗

Parental age and birth order in Alzheimer's disease: a case-control study in the Saguenay-Lac-St-Jean area (Quebec, Canada).

Parental age at the time of birth of 133 clinically diagnosed Alzheimer patients from the Saguenay-Lac-St-Jean area (Quebec, Canada) were compared with those of 6 control groups formed out a population registry. The birth order of the Alzheimer patients was also analyzed. The results did not show any parental age or birth order effect, which is in agreement with previous reports. The importance of control selection in such studies is stressed.

Adult↗

Birth order, family structure and personality variables.

The birth order and family structure variables assessed included first or only child, position in multi-child family, position in dyadic family, age of parents at birth of given child, whether reared by one or both parents, whether reared under permissive or authoritarian family atmosphere. The personality variables assessed included Sociability, Anxiety, Dominance, Superego, Phlegmatic Temperament, Involvement, Self-Regard and other scales measured by the Howarth Personality Questionnaire. One hundred seventy female and 142 male undergraduates were tested. Significant relationships found included: anxiety lower in firstborns; superego higher in firstborns; persistence higher in those not dominated by elder sibling; phlegmatic temperament higher in permissive families; involvement and phlegmatic temperament lower in single parent families; self-pride higher in the elder of a sibling pair; individual tolerance higher in children reared by both rather than single parent.

Journal Article↗

Social class, birth order, and newborn experience.

Early home experiences of a group of 32 2-week old infants, equally divided according to social class, birth order, and sex, were studied. Naturalistic observations were taken on 2 consecutive days for a total of 6 hours. Compared with later-borns, firstborns received significantly more caretaker interaction on all variables studied. Compared with lower-SES infants, those from higher-SES homes received significantly more direct verbal interaction although the 2 groups did not differ on total periods of other types of caretaking interaction. The findings are consistent with birth order and social class differences reported in home environments of older infants and children.

Birth Order↗

Birth forecasting based on birth order probabilities, with application to U.S. data.

"A model for birth forecasting based on prediction of the so-called 'birth order probabilities' is constructed. The relation between this model and recent models of fertility prediction is derived. Birth forecasts with approximate probability limits for the U.S. for the period 1983-1997 are generated. The performance of the proposed model in predicting future fertility is tested by fitting time series models to part of the available series (1917-1982) and ultimately generating birth forecasts for the remainder of the period, then comparing these forecasts with the actual data." The accuracy of the fertility forecasts made are compared with those made by other methods.

Americas↗

Association of childhood leukemia with maternal age, birth order, and paternal occupation. A case-control study.

Previous investigations have drawn conflicting conclusions concerning the association between childhood leukemia and maternal age, birth order, socioeconomic status, and paternal occupation. In this study, 255 childhood leukemia cases diagnosed in California between 1975 and 1980 were individually matched with two living controls on the basis of sex, date of birth, and county of birth. Data were derived from subjects' birth certificates. Socioeconomic status and paternal benzene exposure were determined from the paternal occupation stated on the birth certificate. Hispanics and males were overrepresented in the case group. Cases were also less likely to be of birth order one. No difference was found between case and control groups for maternal age or paternal occupation. Analyses with stratification on age, sex, and leukemia cell type are reported.

Adolescent↗

Birth order and sexual orientation in women.

One of the world's largest databases on human sexuality was used to investigate whether lesbians, like homosexual men, have a later birth order relative to heterosexual comparisons. The women (N > 5,000) were interviewed by investigators at the Kinsey Institute for Sex and Reproduction from 1938 to 1963. The women were dichotomously classified as lesbian (n = 257) or heterosexual (n = 5,008). No significant birth order effect was observed. Results support theories of gender-specific mechanisms in the development of sexual orientation in women and men.

Adult↗

Birth order, family size, and children's use of physician services.

The purpose of this study is to separate out the effects of number of siblings and birth order on children's use of physician services. Prior research has consistently revealed an inverse relationship between family size and physician visits, but the possible confounding influence of the child's ordinal position in the family has been ignored. Later born children may be taken to the doctor less often than first and other early borns because of their parents' increasing knowledgeability in regard to child care as well as their growing understanding of the uses and limitations of physician visits. On the assumption that part of the family size effect observed in prior research may have been due to the clustering of first and early borns in small families, an inverse relationship between birth order and physician utilization is hypothesized. Support for this hypothesis comes from an empirical study of 1,665 children from 587 families in which variation in family size is statistically controlled.

Adult↗

Concentrations of sex hormones in umbilical-cord blood: their relation to sex and birth order of infants.

In 3 groups of human newborns, 5 sex hormones were assayed from samples of umbilical-cord blood, and concentrations were analyzed by the sex and birth order of the infants. The 5 hormones assayed were testosterone, androstenedione, estrone, estradiol, and progesterone. Concentrations of testosterone were significantly greater in males than females. The other 4 hormones did not differ significantly by sex. In both sexes, firstborns had significantly more progesterone and estrogens, with progesterone showing the largest birth-order effects. Among male infants, firstborns had higher concentrations of testosterone. The higher concentrations of progesterone in firstborns of both sexes, and of testosterone in firstborn boys, were found not to be due to length of labor, birth weight, or maternal age. However, they were a function of temporal spacing of childbirths. Later borns who were closely spaced in relation to their next-older siblings had lower concentrations of hormones. The effect of temporal separation was greater on male than female infants for each of the 5 hormones studied. The results are discussed in terms of the possible effects of hormone "depletion" on the psychological development of closely spaced later borns.

Androstenedione↗