During pregnancy, regular checkups are very important. This consistent care can help keep you and your baby healthy, spot problems if they occur, and prevent problems during delivery.

Typically, routine checkups occur:
• Once each month for weeks four through 28
• Twice a month for weeks 28 through 36
• Weekly for weeks 36 to birth

Women with high-risk pregnancies need to see their doctors more often.

At your first visit your doctor will perform a full physical exam, take your blood for lab tests, and calculate your due date. Ultrasound examinations will be done at your visits

Source
https://www.womenshealth.gov/pregnancy/youre-pregnant-now-what/prenatal-care