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Lesson 10: Fetal Positions and Adaptations


   

10-1. GENERAL

The nursing care you may administer to the laboring patient is included in this lesson by presenting key factors in the relationship of the fetus to the obstetric passageway. You may not actually determine this information, however, it is vital that you have a basic understanding of what the nurse or physician identifies. This information will influence the length of labor, preparations for the delivery room, and the type of complications that may occur.

10-2. KEY TERMS RELATED TO FETAL POSITIONS

a. "Lie" of an Infant. Lie refers to the position of the spinal column of the fetus in relation to the spinal column of the mother. There are two types of lie, longitudinal and transverse. Longitudinal indicates that the baby is lying lengthwise in the uterus, with its head or buttocks down. Transverse indicates that the baby is lying crosswise in the uterus.

b. Presentation/Presenting Part. Presentation refers to that part of the fetus that is coming through (or attempting to come through) the pelvis first.

(1) Types of presentations (see figure 10-1). The vertex or cephalic (head), breech, and shoulder are the three types of presentations. In vertex or cephalic, the head comes down first. In breech, the feet or buttocks comes down first, and last--in shoulder, the arm or shoulder comes down first. This is usually referred to as a transverse lie.

Figure 10-1. Typical types of presentations.

(2) Percentages of presentations.

(a) Head first is the most common-96 percent.

(b) Breech is the next most common-3.5 percent.

(c) Shoulder or arm is the least common-5 percent.

(3) Specific presentation may be evaluated by several ways.

(a) Abdominal palpation-this is not always accurate.

(b) Vaginal exam--this may give a good indication but not infallible.

(c) Ultrasound--this confirms assumptions made by previous methods.

(d) X-ray--this confirms the presentation, but is used only as a last resort due to possible harm to the fetus as a result of exposure to radiation.

c. Attitude. This is the degree of flexion of the fetus body parts (body, head, and extremities) to each other. Flexion is resistance to the descent of the fetus down the birth canal, which causes the head to flex or bend so that the chin approaches the chest.

(1) Types of attitude (see figure 10-2).

A--Complete flexion. B-- Moderate flexion. C--Poor flexion. D--Hyperextension

Figure 10-2. Types of attitudes.


Flexed head


Neutral position head

Deflexed head

(a) Complete flexion. This is normal attitude in cephalic presentation. With cephalic, there is complete flexion at the head when the fetus "chin is on his chest." This allows the smallest cephalic diameter to enter the pelvis, which gives the fewest mechanical problems with descent and delivery.

(b) Moderate flexion or military attitude. In cephalic presentation, the fetus head is only partially flexed or not flexed. It gives the appearance of a military person at attention. A larger diameter of the head would be coming through the passageway.

(c) Poor flexion or marked extension. In reference to the fetus head, it is extended or bent backwards. This would be called a brow presentation. It is difficult to deliver because the widest diameter of the head enters the pelvis first. This type of cephalic presentation may require a C/Section if the attitude cannot be changed.

(d) Hyperextended. In reference to the cephalic position, the fetus head is extended all the way back. This allows a face or chin to present first in the pelvis. If there is adequate room in the pelvis, the fetus may be delivered vaginally.

(2) Areas to look at for flexion.

(a) Head-discussed in previous paragraph, 10-2c(1).

(b) Thighs-flexed on the abdomen.

(c) Knees-flexed at the knee joints.

(d) Arches of the feet-rested on the anterior surface of the legs.

(e) Arms-crossed over the thorax.

(3) Attitude of general flexion. This is when all of the above areas are flexed appropriately as described.

Figure 10-3. Measurement of station.

d. Station. This refers to the depth that the presenting part has descended into the pelvis in relation to the ischial spines of the mother's pelvis. Measurement of the station is as follows:

(1) The degree of advancement of the presenting part through the pelvis is measured in centimeters.

(2) The ischial spines is the dividing line between plus and minus stations.

(3) Above the ischial spines is referred to as -1 to -5, the numbers going higher as the presenting part gets higher in the pelvis (see figure10-3).

(4) The ischial spines is zero (0) station.

(5) Below the ischial spines is referred to +1 to +5, indicating the lower the presenting part advances.

e. Engagement. This refers to the entrance of the presenting part of the fetus into the true pelvis or the largest diameter of the presenting part into the true pelvis. In relation to the head, the fetus is said to be engaged when it reaches the midpelvis or at a zero (0) station. Once the fetus is engaged, it (fetus) does not go back up. Prior to engagement occurring, the fetus is said to be "floating" or ballottable.


 

LESSON OBJECTIVES

10-1. Identify key terms and definitions that are related to fetal positions.

10-2. Identify the two types of "lie" positions of an infant.

10-3. Identify the three types of fetal presentations.

10-4. Identify the four types of attitudes seen during the birth process.

10-5. Identify descriptive statements referring to the station of the fetus during labor.

10-6. Identify descriptive statements, which refer to the specific points and positions of the fetus during labor and delivery.

10-7. Identify the different types of breech presentations.

10-8. Identify descriptive statements referring to the mechanism of labor.

 

 

   

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