It can take some time from the first signs of labour until the start of the actual childbirth. Especially during a first pregnancy the labour can be longer. You should come to the hospital if you have contractions every 5-7 minutes during a first pregnancy and 6-10 from your second pregnancy on. If you are in doubt you can contact the midwife by phone at 011 69 98 41.
Naturally you may also come in case of blood loss, if you feel unwell and/or if you have lost the amniotic fluid.