Are Vaginal Exams Necessary in Labor?

Short answer: No, but they're YOUR choice!
This exam allows the physician to know the status of your cervix...whether it's dilated, ripe, or effaced, and baby's position. However, the physical changes to your cervix aren't the only indicators of a progressive labor. You also need strong and effective contractions and a change in your behavior, where you become much more focused.
Many women don't know they can actually decline vaginal exams during labor. Studies show that routine vaginal exams during labor tend to lead to more interventions and aren't accurate because they're based on the staff's perception. A nurse might declare you to be 6 cm dilated but later an OB with much larger hands might say you're actually 5 cm dilated. Risk of infection also increases every time a check is performed, especially if your water has broken. Also, they hurt like a mother!
One of the biggest drawbacks to this exam is that it can negatively affect the laboring person's resolve and determination. If you're feeling great and in control but are then told you're not as dilated as you feel or haven't dilated enough since your last exam (failure to progress), then you'll likely stress out and begin feeling hopeless. These negative emotions will release stress hormones which can actually stall your labor.
That being said, if you really want to know how dilated you are... the recommendation is no more than one exam every 4 hours and be sure to always get CONSENT. It's important to let your provider know how you feel about vaginal exams during your prenatal visits. Be sure they understand your concerns, support your choice, and are able to provide you evidence-based reasons as to why they believe they are necessary. 
Remember that you're more than a number!

---