Newsflash! There's more to labor progress than how many centimeters your cervix dilates. Yes, moms need to reach the magic number 10 (also known as fully dilated) but there is so much more to labor progress before you hold your newborn in your arms.
Your baby needs to be in the right presentation and position
Presentation means the part of the baby that "presents" over your cervix. Most babies present head down and this is the ideal presentation for labor. Your doctor or midwife will check for baby's presentation and if baby is breech, there are things to try to turn him. Once labor begins, ideally your baby will position himself facing down — this usually makes the labor process smoother for him and for you. If your baby is in the face up position, you may experience back labor and it may be more difficult for him to rotate.
Three things need to happen to your cervix
It's not just about dilation. Before that can even happen, your cervix first needs to ripen (soften.) When you're not pregnant, your cervix is long and firm. Toward the end of the third trimester as you near your due date, your body will release prostaglandin to help soften the cervix. Once it's ripe, the cervix will efface (shorten). Effacement is measured in percentages — if your doctor says, "You're 50 percent effaced," that means your cervix is shortening and thinning out halfway to 100 percent effaced. Then comes the much awaited dilation. The opening of your cervix needs to go from zero centimeters (closed) to 10 (fully dilated.) Think of your cervix this way — the size of a Cheerio is about one centimeter, the size of a snack cracker is about five, and a large rice cake is about 10. Hopefully I didn't turn you off to eating those foods again, but it really is a good analogy!
Your baby needs to descend into your pelvis
Pelvic station is another important part of labor progress. Your baby will gradually start his descent into your pelvis as you near your due date, and your doctor can feel how low the baby is when she does an internal exam during your prenatal visit. If she says your baby is "engaged" or at "zero station" this means the widest part of the head is between the ischial spines of your pelvis. It usually takes the hard work of labor — contractions, labor positions that use gravity and the other body changes I mentioned -- to help push a baby into and ultimately through your pelvis into your vagina.
Bottom Line^ All of these things need to fall into place to have a vaginal birth. As long as there are no medical complications for you or your baby, your body will take the time it needs for labor to progress. Be sure to talk to your doctor or midwife if you have any questions. Good luck!