Factors influencing the sex ratio at birth in Australia, 1902–65

Pollard, Gayle

doi:10.1017/s002193200000715x

Cited by 17 publications

(11 citation statements)

References 13 publications

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“…Our study indicated that multiple births have a lower sex ratio than singletons, which was consistent with results from the previous studies [ 31 , 38 , 39 ]. In addition, we demonstrated a higher rate of stillbirths in males among multiple births.…”

Section: Discussionsupporting

confidence: 93%

Neonatal outcomes in relation to sex differences: a national cohort survey in Taiwan

2015

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BackgroundAn extensive assessment investigating the association between sex differences and neonatal outcomes is lacking. In the current study, we estimated the correlation of gender with adverse birth outcomes in a large cohort population.MethodsNational population-based data containing maternal and neonatal information in 2001 to 2010 were derived from the Health Promotion Administration, Taiwan. Singletons without high-risk pregnancy were further analyzed for the sex ratio of live births in relation to neonatal outcomes—including preterm birth, birth weight, neonatal death, delivery mode, and congenital anomaly. A multivariate logistic regression model was used to adjust for possible confounders.ResultsIn total, 2,123,100 births were valid for the analysis. Overall, the sex ratio at birth (male/female) was 1.096. Compared to multiple births, the sex ratio was significantly higher with singleton births (p < 0.001). Among multiple births, the incidence of stillbirths was significantly higher in males than in females (p < 0.05). The sex ratio at gestational age (GA) <37 weeks was 1.332, and it declined proportionally with a rise in the GA to 0.899 at GA of ≥41 weeks. In contrast, the sex ratio was 0.850 at birth weight <3000 g, and it rose proportionally with a rise in the birth weight to 1.902 at birth weight ≥4000 g (macrosomia). Operative delivery was more common in males than in females (p < 0.001). The regression analysis showed greater risks of preterm birth, macrosomia, operative delivery, neonatal death, and congenital anomaly among male newborns.ConclusionsMale gender carried higher risks of adverse neonatal outcomes, including preterm birth, macrosomia, operative delivery, neonatal death, and congenital anomaly. The data have clinical implications on health surveillance for plotting strategies in response to the unbalanced sex ratio in relation to the boy preference.

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Section: Discussionsupporting

confidence: 93%

Neonatal outcomes in relation to sex differences: a national cohort survey in Taiwan

2015

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“…Pollard (1969) studied the sex radio in Australia, 1902-1965, McMahan (1951 in the United States, 1915-1948, and Seki (1968 in England and Wales, 1900-1965, and in France, 1900-1964. The regression coefficients of the sex ratio on year in Australia during the period from 1902 to 1976 (Sources: Pollard, 1969; Official Year Book of The Commonwealth of Australia, 1969;Births, 1976) , 1973;Monthly Vital Statistics Report, 1976), and 0.000101+0.000007, respectively. These values are significant at the 1~, 5~, and 1~ levels, respectively.…”

Section: Discussionmentioning

confidence: 99%

The changing sex ratio in Japan

Imaizumi

Murata²

1981

Jap J Human Genet

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SummaryThe simultaneous effects of maternal age and birth order on the secondary sex ratio have been examined using data on about 59 million births which occurred in Japan during the period from 1947 to 1978 except 1950. Non-linear negative association between the sex ratio and birth order was observed.The secondary sex ratio in Japan has been increasing during the period of 1900 through 1978. The change in birth order distribution can explain only a part of the increase in the sex ratio. The decrease in stillbirth rate was not only negatively correlated with the increase in the sex ratio at birth but also with that in fetal deaths. Therefore, it seems that there are some unexplainable factors associated with the increase in the secondary sex ratio other than the decrease in the stillbirth rate. The present results strongly suggest that the true cause of the secular trend in the secondary sex ratio in Japan will be found in the very early stage of pregnancy or at the time of conception.

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“…These two examples predict opposite trends for human sex ratios with maternal age. Empirical studies have alternatingly found sex ratios to increase (Takahashi ), decrease (Pollard ; James and Rostron ), or be uncorrelated with maternal age (Almagor et al. ; Jacobsen et al.…”

Section: Case 1: Maternal Agementioning

confidence: 99%

“…These two examples predict opposite trends for human sex ratios with maternal age. Empirical studies have alternatingly found sex ratios to increase (Takahashi 1954), decrease (Pollard 1969;James and Rostron 1985), or be uncorrelated with maternal age (Almagor et al 1998;Jacobsen et al 1999). These mixed results may suggest that the effects of various offspring costs vary or even counterbalance in different populations, or that there are additional factors at play.…”

Section: Case 1: Maternal Agementioning

confidence: 99%

Frequency‐dependent two‐sex models: a new approach to sex ratio evolution with multiple maternal conditions

Shyu

Caswell

2016

Ecology and Evolution

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Mothers that experience different individual or environmental conditions may produce different proportions of male to female offspring. The Trivers‐Willard hypothesis, for instance, suggests that mothers with different qualities (size, health, etc.) will use different sex ratios if maternal quality differentially affects sex‐specific reproductive success. Condition‐dependent, or facultative, sex ratio strategies like these allow multiple sex ratios to coexist within a population. They also create complex population structure due to the presence of multiple maternal conditions. As a result, modeling facultative sex ratio evolution requires not only sex ratio strategies with multiple components, but also two‐sex population models with explicit stage structure. To this end, we combine nonlinear, frequency‐dependent matrix models and multidimensional adaptive dynamics to create a new framework for studying sex ratio evolution. We illustrate the applications of this framework with two case studies where the sex ratios depend one of two possible maternal conditions (age or quality). In these cases, we identify evolutionarily singular sex ratio strategies, find instances where one maternal condition produces exclusively male or female offspring, and show that sex ratio biases depend on the relative reproductive value ratios for each sex.

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Factors influencing the sex ratio at birth in Australia, 1902–65

Cited by 17 publications

References 13 publications

Neonatal outcomes in relation to sex differences: a national cohort survey in Taiwan

Neonatal outcomes in relation to sex differences: a national cohort survey in Taiwan

The changing sex ratio in Japan

Frequency‐dependent two‐sex models: a new approach to sex ratio evolution with multiple maternal conditions

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