Students Staff

28 July 2012

Working through pregnancy can lead to low birth-weight, study finds

Expectant mothers who work up to their due date are likely to have babies with a lower birth-weight, a new study has revealed. The effect is particularly marked for older women.

Research carried out at the University of Essex revealed women who worked after they were eight months pregnant had babies which were on average around half a pound lighter than those who stopped work between six and eight months.

The study, which drew on data from three major longitudinal studies, two in the UK and one in the US, found the effect of continuing to work during the late stages of pregnancy was equal to that of smoking while pregnant.

Babies whose mothers worked or smoked throughout pregnancy also grew more slowly in the womb. Past research has shown babies with low birth weights are at higher risks of poor health and slow development, and may suffer from multiple problems later in life.

Stopping work early in pregnancy was particularly beneficial for women with lower levels of education, the study found – suggesting that the effect of working during pregnancy was possibly more marked for those doing physically demanding work.

The birth weight of babies born to mothers under the age of 24 was not affected by them continuing to work, but in older mothers the effect was more significant.

The researchers identified 912 children whose mothers were part of the British Household Panel Survey, a longitudinal study conducted between 1991 and 2005, and for whom data was available. A further sample of 17,483 women who gave birth in 2000 or 2001 and who took part in the Millennium Cohort Study was also examined and showed similar results, along with 12,166 from the National Survey of Family Growth, relating to births in the US between the early 1970s and 1995.

Professor Marco Francesconi, one of the authors of the study, said the Government should consider incentives for employers to offer more flexible maternity leave to women who might need a break before, rather than after, their babies were born. Babies with low birth weights tended to cost the state more money later on, he said.

“We know low birth weight is a predictor of many things that happen later, including lower chances of completing school successfully, lower wages, and higher mortality. We need to think seriously about parental leave, because – as this study suggests - the possible benefits of taking leave flexibly before the birth could be quite high.”

The study also suggests British women may be working for longer during pregnancy: while 16 per cent of mothers questioned by the British Household Panel Study, which went as far back as 1991, worked up to one month of the birth, 30 per cent of those in the Millennium Cohort Study (MCS) whose subjects were born in 2000 and 2001, did so.

The research was conducted by three economists, Marco Francesconi, Emilia Del Bono and John Ermisch.


The paper, Intrafamily Resource Allocations: A Dynamic Structural Model of Birth Weight, by Dr Emilia Del Bono, Professor John Ermisch and Professor Marco Francesconi, is published in the July edition of the Journal of Labor Economics, published by the University of Chicago, and is attached. Professor John Ermisch has recently moved to the University of Oxford, but this research was carried out while he was based at the Institute of Social and Economic Research at the University of Essex.

The team identified 1,339 babies whose mothers who took part in the British Household Panel Survey, conducted between 1991 and 2005, for whom information was available, along with 17,483 from the Millennium Cohort Study in the UK and 12,166 from the National Survey of Family Growth, which relates to births in the US between the early 1970s and 1995.

The study was supported in part by a grant from the Economic and Social Research Council.

For more details or an interview with Professor Francesconi, please contact Fran Abrams, Communications Officer, on 07939 262001 or at

Professor Francesconi can be contacted directly via email at

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