As labor progresses, sinciput and brow presentations almost always convert into vertex or face presentations by neck flexion or extension, respectively. These latter two presentations are usually transient. The fetal head may assume a position between these extremes, partially flexed in some cases, with the anterior (large) fontanel, or bregma, presenting- sinciput presentation-or partially extended in other cases, to have a brow presentation ( Fig. ![]() Much less commonly, the fetal neck may be sharply extended so that the occiput and back come in contact, and the face is foremost in the birth canal- face presentation ( Fig. The occipital fontanel is the presenting part, and this presentation is referred to as a vertex or occiput presentation. Ordinarily, the head is flexed sharply so that the chin is in contact with the thorax. Such presentations are classified according to the relationship between the head and body of the fetus ( Fig. Fetal Presentation in 68,097 Singleton Pregnancies at Parkland Hospital Table 22-1 describes the incidences of the various fetal presentations. When the fetus lies with the long axis transversely, the shoulder is the presenting part. Accordingly, in longitudinal lies, the presenting part is either the fetal head or breech, creating cephalic and breech presentations, respectively. It typically can be felt through the cervix on vaginal examination. The presenting part is that portion of the fetal body that is either foremost within the birth canal or in closest proximity to it. Predisposing factors for transverse fetal position include multiparity, placenta previa, hydramnios, and uterine anomalies ( Chap. A longitudinal lie is present in more than 99 percent of labors at term. This lie is unstable and becomes longitudinal or transverse during labor. Occasionally, the fetal and the maternal axes may cross at a 45-degree angle, forming an oblique lie. ![]() The relation of the fetal long axis to that of the mother is termed fetal lie and is either longitudinal or transverse. Important relationships include fetal lie, presentation, attitude, and position. 588).Īt the onset of labor, the position of the fetus with respect to the birth canal is critical to the route of delivery and thus should be determined in early labor. Determining which aspects of childbirth contribute most to this risk has become an area of intense investigation and discussed further in Chapter 30 ( p. This understanding of normal labor and delivery as a physiological process has come under some scrutiny in the past decade because pelvic floor disorders have been observed to be more prevalent among women who have delivered at least one child (Handa, 2011 Nygaard, 2008). It is undoubtedly true that pregnancy and birth are physiological processes, and as such, labor and delivery should be considered to be normal for most women (Lawrence, 2012). The term labor in the obstetrical context takes on several connotations from the English language. It begins with the onset of regular uterine contractions and ends with delivery of the newborn and expulsion of the placenta. Labor is the process that leads to childbirth. Williams Obstetrics, 24th Edition CHAPTER 22.
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