How often are vaginal exams performed during labour?

When I checked in hospital, I was already 5cm dilated for my first delivery. Thus, nurses came and check every half hour. If you have strong urge to push (like poop), you need to quickly inform the mid-wife about it as it might be fully dilated already. For my 2nd delivery, I was 5cm too when checked in hospital but I dilated fully within 15minutes. I screamed to nurse I need to push and they checked I was 10cm dilated already.