Biomaterial Database

Secondary sex ratio in multiple births. 2010

Johan Fellman, and Aldur W Eriksson

Folkhälsan Institute of Genetics, Department of Genetic Epidemiology, Helsinki, Finland. johan.fellman@shh.fi

Attempts have been made to identify factors influencing the sex ratio at birth (number of males per 100 females). Statistical analyses have shown that comparisons between sex ratios demand large data sets. The secondary sex ratio has been believed to vary inversely with the frequency of prenatal losses. This hypothesis suggests that the ratio is highest among singletons, medium among twins and lowest among triplets. Birth data in Sweden for the period 1869-2004 showed that among live births the secondary sex ratio was on average 105.9 among singletons, 103.2 among twins and 99.1 among triplets. The secondary sex ratio among stillbirths for both singletons and twins started at a high level, around 130, in the 1860s, but approached live birth values in the 1990s. This trend is associated with the decrease and convergence of stillbirth rates among males and females. For detailed studies, we considered data for Sweden in 1869-1878 and in 1901-1967. Marital status or place of residence (urban or rural) had no marked influence on the secondary sex ratio among twins. For triplets, the sex ratio showed large random fluctuations and was on average low. During the period 1901-1967, 20 quadruplet, two quintuplet and one sextuplet set were registered. The sex ratio was low, around 92.0.

UI	MeSH Term	Description	Entries
D007231	Infant, Newborn	An infant during the first 28 days after birth.	Neonate,Newborns,Infants, Newborn,Neonates,Newborn,Newborn Infant,Newborn Infants
D008297	Male		Males
D009099	Multiple Birth Offspring	The offspring in multiple pregnancies (PREGNANCY, MULTIPLE): TWINS; TRIPLETS; QUADRUPLETS; QUINTUPLETS; etc.	Sextuplets,Multiple Birth,Multiple Births,Birth Offspring, Multiple,Birth, Multiple,Offspring, Multiple Birth,Sextuplet
D005260	Female		Females
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D012744	Sex Ratio	The number of males per 100 females.	Ratio, Sex,Ratios, Sex,Sex Ratios
D013548	Sweden	Country in northern Europe, bordering the Baltic Sea, between Finland and Norway. The capital is Stockholm.
D015233	Models, Statistical	Statistical formulations or analyses which, when applied to data and found to fit the data, are then used to verify the assumptions and parameters used in the analysis. Examples of statistical models are the linear model, binomial model, polynomial model, two-parameter model, etc.	Probabilistic Models,Statistical Models,Two-Parameter Models,Model, Statistical,Models, Binomial,Models, Polynomial,Statistical Model,Binomial Model,Binomial Models,Model, Binomial,Model, Polynomial,Model, Probabilistic,Model, Two-Parameter,Models, Probabilistic,Models, Two-Parameter,Polynomial Model,Polynomial Models,Probabilistic Model,Two Parameter Models,Two-Parameter Model
D016009	Chi-Square Distribution	A distribution in which a variable is distributed like the sum of the squares of any given independent random variable, each of which has a normal distribution with mean of zero and variance of one. The chi-square test is a statistical test based on comparison of a test statistic to a chi-square distribution. The oldest of these tests are used to detect whether two or more population distributions differ from one another.	Chi-Square Test,Chi Square Distribution,Chi Square Test,Chi-Square Distributions,Chi-Square Tests,Distribution, Chi-Square,Distributions, Chi-Square,Test, Chi-Square,Tests, Chi-Square