Understanding Baby's Station: What Does -1 Mean During Labor?

Question
Hi,
At my doctor's appt. today, she told me I was 4cm and 80% effaced and that the baby was at a -1. Although, I understand 40cm and 80%, I wasn't sure about the-1 thing. If you know what I am talking about could you please explain that to me.
Thanks
Essence

Answer
Doctors and midwives use markers on your pelvis and lower spine as measures of how far down the baby has descended.  There are two bony spots inside your pelvis called the ischial spines, and these mark "zero station".  Anything above this is noted as negative, up to -5 if baby is right at your hip bones.  Below the spines is positive, up to +4 when baby is crowning.

Like dilation and effacement, though, station means nothing regarding when you will go into labor or how long labor will take.  Because exams are traditionally done when you are lying down, baby can even float up and appear to be at a higher station than he/she is when you are standing, making this a very inexact measurement.