I completely agree with Kelly. At work (I'm a student midwife) it is always the third baby that throws a spanner in the works. It is either completely different to the other two and are the hardest labours or they absolutely shoot out. I am the third baby and my mum went into hospital and they told her to have a sleep overnight as I won't be coming anytime soon and then 1/2 hours they checked on mum and my head was almost out.
Don't want to alarm you though. Good luck.