Important - we don't eat cows. We eat steer. Cows have been bred over the decades and centuries to give birth and milk, not to yield meat. That's important, because some cows are heavier than their steer counterparts (Holsteins, for example).
Also very dangerous is inducing a miscarriage by taking strong medications prescribed for other ailments and many of the ways to induce a miscarriage can actually end in loss of life or other very serious consequences.
Infections: Research has shown a somewhat higher risk for miscarriage if you have listeria, mumps, rubella, measles, cytomegalovirus, parvovirus, gonorrhea, HIV, and certain other infections. Smoking, drinking, and using drugs: Smoking, drinking alcohol, and using drugs like cocaine and MDMA (ecstasy) during pregnancy can all increase your risk for miscarriage.