Women who work more than 40 hours each week are having difficulty getting pregnant, and there may be a very simple reason why.

It took women who worked more than 40 hours per week about 20 percent longer to conceive, states a new study according to a Daily Mail report.

In addition, women who lifted heavy objects frequently — at least 25 pounds — took even longer to conceive, about 50 percent longer in fact.

That’s based on a study of 1,739 nurses, all of whom were trying to get pregnant. About 16 percent failed to become pregnant within a year, and it took more than two years for 5 percent of them.

Although there wasn’t much different between women who worked night shifts or other factors that might seem to increase stress, one area did appear to have an effect: those who worked a lot, as well as those who worked hard, lifting heavy loads several times per day, with both causing severe delays to conceiving.

It takes a healthy couple about three to six months to conceive usually, although older couples and those with bad diet and smoking habits could take longer on average.

In this study, about half the women were at least 33 years of age, and nearly half of them were overweight. About 22 percent of them were current or former smokers.

But there may be a very simple explanation for this finding, researchers suggested: it may be that those who simply work long hours and do more back-breaking work simply don’t have the time or energy to engage in sexual intercourse.