Your pick: Tramp stamp or Epidural

Lately, a lot of girls have been getting the "tramp stamp," you know the tattoo on the lower lower-er back. But there may be a downside to getting one if you plan on getting painkillers during labor.

In 2002, a pair of Canadian anesthesiologists published a report that questioned whether administering an epidural through such a tattoo could be risky. The doctors speculated that complications like inflammation or nerve damage may arise if the needle pulled a bit of dyed skin along with it, and then deposited it into the nerve-rich region outside the spinal column.
http://online.wsj.com/article/SB119006970692630378.html?mod=todays_us_nonsub_pj

Other doctors say its no big deal if the ink is dried and the wound healed....but the ink itself is not exactly FDA approved. So if you plan on getting one, just remember to deal with it during labor.