Many women experience complications during pregnancy that requires time away from work for bed rest.  Twenty five percent of all pregnancies experience one or more complications that might require bed rest and an extended period of unplanned missed work. 

Should this happen to you your employer may or may not hold your job open for you.  You might have planned to miss six or eight weeks for your normal maternity leave, and maybe you set aside some savings in case you missed more time for complications.