As you approach your due date, you will be looking for any little sign that labor is about to start. You might notice that your baby has "dropped" or moved lower into your pelvis. This is called "lightening." If you have a pelvic exam during your prenatal visit, your doctor might report changes in your cervix that you cannot feel, but that suggest your body is getting ready. For some women, a flurry of energy and the impulse to cook or clean, called "nesting," is a sign that labor is approaching.
Some signs suggest that labor will begin very soon. Call your doctor or midwife if you have any of the following signs of labor. Call you doctor even if it is weeks before your due date — you might be going into preterm labor. Your doctor or midwife can decide if it's time to go to the hospital or if you should be seen at the office first.You have contractions that become stronger at regular and increasingly shorter intervals. You have lower back pain and cramping that does not go away. Your water breaks (can be a large gush or a continuous trickle). You have a bloody (brownish or red-tinged) mucus discharge. This is probably the mucus plug that blocks the cervix. Losing your mucus plug usually means your cervix is dilating (opening up) and becoming thinner and softer (effacing). Labor could start right away or may still be days away.
This answer is based on source information from the National Women's Health Information Center.