Research found that a physically demanding job or work schedules outside of normal office hours may lower a woman’s ability to conceive.
It is the first study of its kind to measure whether workplace factors might affect a woman’s biological capacity to have a baby.
For the study, published in the journal ‘Occupational and Environmental Medicine’, researchers looked at indicators of “ovarian reserve” in 473 women attending one fertility clinic.
The “reserve” refers to a woman’s number of remaining eggs and level of follicle stimulating hormone (FSH), which rises as a woman ages and represents dwindling fertility.
The average age of participants was 35 and they had an average BMI of 23. They were quizzed about the jobs they did, as well as the level of physical exertion required for their roles and the hours and patterns worked.
Researchers discovered that while type of workload did not seem to make any difference to FSH levels, women with physically demanding jobs had a lower reserve of eggs than those whose work did not regularly require heavy lifting.
Among women going through IVF, those with physically demanding jobs had a lower total reserve of eggs and fewer mature eggs - representing reductions of nearly 9% and nearly 14.5%, respectively - when compared with those who didn’t do heavy lifting.
For women working evening, night or rotating shifts, their reserves were found to follow a similar pattern.
These women had fewer mature eggs, on average, than those working shifts within normal working hours. The difference was even greater among those specifically working evening and night shifts, possibly because of disruption to the body clock, researchers suggested.
Women who were overweight (BMI of 25 and above) and whose job was physically demanding, also had fewer mature eggs.
“These findings have clinical implications,” wrote the researchers. “As women with fewer mature oocytes [eggs] would have fewer eggs which are capable of developing into healthy embryos.”
They added that the results “suggest that occupational factors may be more specifically affecting oocyte production and quality, rather than accelerating ovarian ageing”.
Professor Geeta Nargund, medical director of Create Fertility, branded the findings as “very interesting”.
“It is well known that sleep disturbance can have negative impact on hormonal rhythms and metabolism, particularly with melatonin and cortisol levels,” she told The Huffington Post UK.
“An interaction between melatonin and follicle stimulating hormone has been previously reported.
“We need further large studies to confirm these findings before we can advise women if their night shifts have a potential negative impact on their egg quality and IVF outcome.”