Prior to labor there is generally a sequence of predictable events that mark the physiological preparation for delivery of the infant. Beginning 4–8 weeks prior to delivery, the patient may begin to experience slight, irregular, and non-sustained contractions. These contractions, referred to as Braxton–Hicks, are marked by only mild discomfort in most circumstances and do not lead to cervical change.

Approximately 2 weeks prior to delivery, the fetal head will often settle into the pelvic brim. This settling is referred to as lightening and the patient may report that the baby has “dropped.” There is potentially a measurable decrease in fundal height and the patient may report a decrease in pregnancy symptoms related to intra-abdominal pressure. The woman may also, however, report an increase in symptoms related to fetal pressure within the pelvis.

Beginning several days to several weeks prior to delivery, the cervix will begin to undergo preparatory changes that will include softening and may also include some degree of effacement and dilation. Dilation up to 3 cm may occur during this phase and is generally more pronounced in multiparous patients. A standardized measure of cervical condition exists and is often used in the evaluation of patients for possible induction of labor, when necessary. The Bishop scale is summarized in Table 18.1.