A new study, published in the journal Royal Society Open Science, suggests that living in the same household with a woman's mother or mother-in-law may lower the number of children the woman has.
The new research was carried out by Susanne Huber, Patricia Zahourek, and Martin Fieder – all from the Department of Anthropology at the University of Vienna in Austria.
The researchers were prompted to study the effect of living with one's mother or mother-in-law on the young woman's fertility by existing literature, which suggested the opposite: that the presence of the woman's or the husband's mother may increase fertility.
To clarify the effect of a mother's and mother-in-law's presence on fertility, Fieder and colleagues examined the medical records of over 2.5 million women from 14 countries across the globe.
The women were of reproductive age — that is, between 15 and 34 years — and the data were gathered from the IPUMS-International census database.
In their analysis, the researchers considered a variety of variables, including: the number of children the women had given birth to until the census, the woman's age, an estimation of the woman's reproductive period, as well as whether their mother or mother-in-law was present in the household during the woman's reproductive period.