It is thought that most mis­car­riages are the res­ult of ran­dom vari­ations in the chro­mo­somes of the baby. Chro­mo­somes are genetic ‘build­ing blocks’ that guide the devel­op­ment of a baby. If a baby has too many or not enough chro­mo­somes, the preg­nancy can end in mis­car­riage. While a mis­car­riage does not usu­ally ser­i­ously affect a woman’s phys­ical health, it can have a sig­ni­fic­ant emo­tional impact.