A new study published in the Journal of Labor Economics reveals that pregnant women who work right up to their due date were more likely to give birth to babies who have lower birth weight.

The study was conducted by researchers at University of Essex who analyzed data from three major studies in Britain and the US and found that working late into pregnancy has the same effect on the unborn child as smoking during pregnancy and led to slow growth of the baby in the womb.

The researchers added that the findings were limited to mothers over 24 years of age and did not affect those who were younger than 24 and continued to work late into their pregnancies.