Answer: By definition, a misdemeanor refers to a crime for which the penalty is up to one-year jail time. That doesn't mean that your state prescribes jail time for certain misdemeanors. And in addition, it does not mean you will be sentenced to jail time for your first misdemeanor DUI conviction. That depends on several different factors:
Laws that govern DUI penalties are different in every state, and sometimes even different by county. There are a variety of penalties that can be imposed on a person convicted of their first misdemeanor DUI, and in many state can include mandatory minimum jail time. Check your state's laws for first time DUI offenses.
Your driving history, particularly the number of previous alcohol related arrests may influence the determination. For example, in Ohio, you can be sentenced to jail time if you accumulate too many points on your license in too short a period of time. If you already had points on your license, a first DUI conviction could put you over the top and make jail time more likely in your case.
Certain factors may infliuence decisions about incarceration these typically include whether minors were present in the vehicle, the speed of the driver, how excessive the .BAC, and whether the driver resisted arrest.
It's possible that you or your attorney can negotiate for an alternative to jail time -- typically community service. For example, California has a 48 mandatory minimum jail sentence, it can be converted to community service.
An attorney will know the law in your state, and will know how to negotiate the best possible outcome for your situation.