Her contractions are 12 minutes apart.
(a woman's) contractions are (a number of) minutes apart
Contractions usually don't happen contuously throughout child birth. There are periods of rest in between them. As you get closer to having the baby, they happen more and more frequently. A common practice is to measure how much time passes between each contraction, so that you know how close you are to having the baby. We talk about this by saying that the contractions are "___ minutes apart":
A: I'm having my contractions.
B: How far apart are they?
SOURCE: phrasemix.com
