Abstract
Are daughters of older mothers less fertile? The human mutation rate is high and increases with chronological age. As female oocytes age, they become less functional, reducing female chances at successful reproduction. Increased oocyte mutation loads at advanced age may be passed on to offspring, decreasing fertility among daughters born to older mothers. In this paper we study the effects of maternal ageing on her daughter's fertility, including total number of children, age at last birth, and neonatal mortality among her children. We study fertility histories of two generations of women from mutually exclusive families from a pre-demographic transition historical population in the Dutch province of Zeeland. Using mixed effect Poisson and linear models to take within family (sibling) relations into account, we show that among married daughters fertility is reduced for those who were born to mothers with an advanced maternal age, resulting in fewer children ever born and earlier ages at last birth. We do not find consistent evidence for effects on neonatal mortality. These results may indicate that women born to older mothers are negatively affected by their mothers' increased age.
Highlights
Does a mother's advanced age disadvantage her daughters' reproduction? In the past decades, the age at first childbirth has increased
We estimate a Poisson distributed generalized linear mixed model to study the relation between mother's age at birth and the count distribution of 1) number of children, 2) neonatal mortality, in the first four weeks from birth, including infants who were dead upon registration and the Gaussian distribution of 3) age at last birth
Where Yij is a vector of responses for the jth F1 research persons (RPs) of F0 mother i and corresponds to either the number of children and neonatal mortality, or age at last birth. β is a vector of regression coefficients for the main effects of interest (Z) which corresponds to the age of the mother at the time of birth of the RP, γ is a vector of regression coefficients for the effects of covariates and possible confounders (X), which are marriage age, and birth year of the mother. u refers to an unobserved random effect shared by RPs of a given mother
Summary
Does a mother's advanced age disadvantage her daughters' reproduction? In the past decades, the age at first childbirth has increased. Studying the consequences of late reproduction in humans requires multigenerational data from natural fertility populations, before socioeconomic differences in fertility or secular gains in lifespan, public health, and education properly set in. We build upon the work of Gillespie, Russell and Lummaa (2013), who showed that older mothers negatively affect offspring survival and fertility in four historical Finnish parishes These first results are in line with empirical observations from animal studies, the statistical estimates may be more precise in our larger sample. We use historical data on an entire province to assess whether and to what extent age at last childbirth, total number of children, and neonatal mortality are related to the age of the grandmother at the time of birth of the mother
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