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To investigate whether early life characteristics predict subsequent reproductive success in a post-demographic transition population; to ascertain the pathways mediating any observed effects; and to examine whether any of the above effects are gender-specific.
Multi-generational data from a representative, population-based birth cohort and using linkage to routinely collected data.
13 666 individuals born in Uppsala university hospital between 1915 and 1929, who were traced and linked to all registered descendants up to 2002.
Characteristics Measured at Birth
Birthweight for gestational age, preterm birth, birth multiplicity, birth order, mother’s age, mother’s marital status and family socio-economic position.
Measures of Reproductive Success
Primary measures: number of children; number of grandchildren. Secondary measures of the pathways to reproductive success: survival to age 15, survival from age 15 to age 50; probability of marriage; number of children within marriage; number of grandchildren at a given number of children.
Reproductive success was associated with both social and biological characteristics at birth, and the effects of these characteristics were mediated via both mortality and fertility. In both sexes, a higher birthweight for gestational age, a term birth and a younger mother were independently associated with a greater number of descendants. A married mother and higher family socio-economic position were also associated a greater number of descendants in males (but not females), while in females (but not males) higher birth order was associated with higher reproductive success. These differences between the genders were mediated by the differential effects upon the probability of marriage in men and women. Probability of marriage was also affected by a range of other characteristics at birth including a lower probability of marriage for individuals of low birthweight and males who were preterm. Number of grandchildren increased with increasing number of children in both sexes, providing no evidence for a trade-off between quantity of offspring and their subsequent reproductive “quality”.
Early life characteristics can affect reproductive success even in post-demographic transition populations. These effects operate via multiple pathways and include “biological” characteristics such as birthweight having an effect via social facts such as adult marital status. These findings can inform analyses of reproductive career as a determinant of health in later life in this and other similar populations. They also generate hypotheses regarding the potential long term consequences of adverse early environments in concurrent cohorts around the world.
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