Initial (Latent) Phase
Contractions are irregular at first but become progressively stronger and more rhythmic.
Discomfort is minimal.
The cervix begins to thin and opens to about 1 1/2 inches (4 centimeters).
The initial phase lasts an average of 8 hours (usually no more than 20 hours) in a first pregnancy and 5 hours (usually no more than 12 hours) in subsequent pregnancies.