One of the first signs of labor is the thinning and softening of the cervix, or a process known as effacing. This is not something that you will feel, but in the weeks leading up to your active labor, the cervix begins to thin out. Usually, the thickness of the cervix is at 4 cm and this gradually decreases in measurement (i.e. 50% effaced is 2 cm). You need to be 100 percent effaced before you can deliver a child through the vagina.
Another step of labor is cervical dilation or when the cervix begins to open up. The doctor measures the dilation from a range of 1-10 centimeters. This is not an indicator of when labor actually begins, but is a sign that you are on your way. Some women reportedly spend days at a certain dilation range for days before labor begins. These changes are slow in the beginning but while in active labor the dilation occurs more quickly.
Another sign of labor is the loss of the mucous plug. There is a thick mucous that plugs the opening of the cervix which serves to protect the baby from infections. As birth draws near, the cervix sheds this mucous plug and you may notice a thick, stringy mucous discharge which is brownish in color or tinged with blood. While this is an indication that labor is coming, it is not a good indicator of when you will enter active labor.
You might also experience a phenomenon called nesting, wherein the mother experiences a strong spurt of energy that is geared towards preparing the environment for the newborn. You may experience the strong urge to decorate, clean up and prep the crib during this time. It is theorized that this is an instinctive trait which draws its origins from when our ancestors needed to do physical work in order to prepare their bodies for childbirth. Try not to exert too much effort and instead reserve your strength for when you are about to give birth.
The next phase of labor is when the contractions begin. Contractions occur as a way of warming up your body for labor. In the beginning the contractions may not be too painful, mostly just inconvenient. As you get deeper into labor, the spasms will become more frequent and more painful. True contractions usually take somewhere between 30 seconds and 90 seconds. Your doctor will time the contractions and based on this may determine whether you are ready to give birth.