Women who work shift work could face more problems trying to conceive.
Researchers at Harvard University also found that those in physically demanding jobs could find it harder to have a baby.
The study involved two groups of women undergoing IVF.
Scientist suggest stress caused by working irregular hours could affect normal hormone production.
Also the body's response to repetitive physical stress can affect the production of good quality eggs.
Susan Keogh has been speaking to Dr John Kennedy Medical Director at the SIMS fertility clinic about the study:
