When do drs start checking for dilation

(Rebecca) • Im 33wife married 14 years and have 3 boys 14,9,3
This is baby #3 and it's been 6 years since I had a baby and I was curious when the doctor starts checking for dilation? Also when u start going every 2 weeks to the dr? Im 28 weeks 3 days tomarrow im still a ways off before my due date just was curious to when I have to look foward to.