FETAL POSITIONS AND ADAPTATIONS
10.0 Introduction and Key Terms Related to Fetal Positions
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.
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).
Figure 10-2. Types of attitudes. A--Complete flexion. B-- Moderate flexion. C--Poor flexion. D--Hyperextension
- (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-iscussed 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.
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.
Figure 10-3. Measurement of station.
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.
f. Position. This is the relationship between a predetermined point of reference or direction on the presenting part of the fetus to the pelvis of the mother.
(1) The maternal pelvis is divided into quadrants.
- (a) Right and left side, viewed as the mother would.
- (b) Anterior and posterior. This is a line cutting the pelvis in the middle from side to side. The top half is anterior and the bottom half is posterior.
- (c) The quadrants never change, but sometimes it is confusing because the student or physician's viewpoint changes.
NOTE: Remember that when you are describing the quadrants, view them as the mother would.
(2) Specific points on the fetus.
(a) Cephalic or head presentation.
- 1 Occiput (O). This refers to the Y sutures on the top of the head.
- 2 Brow or fronto (F). This refers to the diamond sutures or anterior fontanel on the head.
- 3 Face or chin presentation (M). This refers to the mentum or chin.
(b) Breech or butt presentation.
- 1 Sacrum or coccyx (S). This is the point of reference.
- 2 Breech birth is associated with a higher perinatal mortality.
(c) Shoulder presentation.
- 1 This would be seen with a transverse lie.
- 2. Scapula (Sc) or its upper tip, the acromion (A) would be used for the point of reference.
(3) Coding of positions.
(a) Coding simplifies explaining the various positions.
- 1 The first letter of the code tells which side of the pelvis the fetus reference point is on (R for right, L for left).
- 2 The second letter tells what reference point on the fetus is being used (Occiput-O, Fronto-F, Mentum-M, Breech-S, Shoulder-Sc or A).
- 3 The last letter tells which half of the pelvis the reference point is in (anterior-A, posterior-P, transverse or in the middle-T).
(b) Each presenting part has the possibility of six positions. They are normally recognized for each position--using "occiput" as the reference point.
- 1 Left occiput anterior (LOA).
- 2 Left occiput posterior (LOP).
- 3 Left occiput transverse (LOT).
- 4 Right occiput anterior (ROA).
- 5. Right occiput posterior (ROP).
- 6 Right occiput transverse (ROT).
(c) A transverse position does not use a first letter and is not the same as a transverse lie or presentation.
- 1 Occiput at sacrum (O.S.) or occiput at posterior (O.P.).
- 2 Occiput at pubis (O.P.) or occiput at anterior (O.A.).
(4) Types of breech presentations (see figure10-4).
(a) Complete or full breech. This involves flexion of the fetus legs. It looks like the fetus is sitting in a tailor fashion. The buttocks and feet appear at the vaginal opening almost simultaneously.
Figure 10-4. Breech positions. A--Complete. B--Frank. C--Incomplete.
- (b) Frank and single breech. The fetus thighs are flexed on his abdomen. His legs are against his trunk and feet are in his face (foot-in-mouth posture). This is the most common and easiest breech presentation to deliver.
- (c) Incomplete breech. The fetus feet or knees will appear first. His feet are labeled single or double footing, depending on whether 1 or 2 feet appear first.
(5) Observations about positions (see figure 10-5).
- (a) LOA and ROA positions are the most common and permit relatively easy delivery.
- (b) LOP and ROP positions usually indicate labor may be longer and harder, and the mother will experience severe backache.
Figure 10-5. Examples of fetal vertex presentations in relation to quadrant of maternal pelvis.
(c) Knowing positions will help you to identify where to look for FHT's.
- 1 Breech. This will be upper R or L quad, above the umbilicus.
- 2 Vertex. This will be lower R or L quad, below the umbilicus.
- (d) An occiput in the posterior quadrant means that you will feel lumpy fetal parts, arms and legs (see figure 10-5 A). If delivered in that position, the infant will come out looking up.
- (e) An occiput in the anterior quadrant means that you will feel a more smooth back (see figure 10-5 B). If delivered in that position, the infant will come out looking down at the floor.