Childbirth is the period from the onset of regular uterine contractions until expulsion of the placenta. The process by which this normally occurs is called labor—a term that in the obstetrical context takes on several connotations from the English language. According to the New Shorter Oxford English Dictionary (1993), toil, trouble, suffering, bodily exertion, especially when painful, and an outcome of work are all characteristics of labor and thus implicated in the process of childbirth. Such connotations all seem appropriate to us and emphasize the need for all attendants to be supportive of the laboring woman's needs, particularly in regard to effective pain relief.
At Parkland Hospital in 2007, only 50 percent of 13,991 women with singleton cephalic presentations at term had a spontaneous labor and delivery. The remainder had ineffective labor requiring augmentation, had other medical and obstetrical complications requiring induction of labor, or underwent cesarean delivery. It seems excessive to consider 50 percent of parturients as “abnormal” because they did not spontaneously labor and deliver. Hence, the distinction between normal and abnormal is often subjective. This high prevalence of labor abnormalities, however, can be used to underscore the importance of labor events in the successful outcome of pregnancy.
At the onset of labor, the position of the fetus with respect to the birth canal is critical to the route of delivery. Thus, fetal position within the uterine cavity should be determined at the onset of labor.
Fetal Lie, Presentation, Attitude, and Position
Fetal orientation relative to the maternal pelvis is described in terms of fetal lie, presentation, attitude, and position.
The relation of the fetal long axis to that of the mother is termed fetal lie and is either longitudinal or transverse. Occasionally, the fetal and the maternal axes may cross at a 45-degree angle, forming an oblique lie, which is unstable and always becomes longitudinal or transverse during labor. A longitudinal lie is present in greater than 99 percent of labors at term. Predisposing factors for transverse lies include multiparity, placenta previa, hydramnios, and uterine anomalies (see Chap. 20, Transverse Lie).
The presenting part is that portion of the fetal body that is either foremost within the birth canal or in closest proximity to it. It can be felt through the cervix on vaginal examination. Accordingly, in longitudinal lies, the presenting part is either the fetal head or breech, creating cephalic and breech presentations, respectively. When the fetus lies with the long axis transversely, the shoulder is the presenting part and is felt through the cervix on vaginal examination. Table 17-1 describes the incidences of the various fetal presentations.
Table 17-1. Fetal Presentation in 68,097 Singleton Pregnancies at Parkland Hospital