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Calculating the Expected Date of Delivery (E.D.D.) 2 страница
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A. 1 g daily
B. 10 g daily
C. 5 g daily
4. The necessity in calcium at pregnancy is:
A. increased
B. decreased
5. A daily dose of carotin in pregnancy is:
A. about 1. 5 mg
B. 10 mg
C. 50 mg
6. A daily dose of vitamin E for pregnant is:
A. 10-15 mg
B. 5-10mg
C. 20-25 mg
7. Physical exercises are contraindicated to pregnant with:
A. gestosis
B. obesity
C. constipation
8. A daily need of vitamin D for pregnant is:
A. 1, 000 IU
B. 2, 000 IU
C. 3, 000 IU
9. An average daily norm of protein in the second half of pregnancy is:
A. 2 g/kg
B. 3 g/kg
C. 5 g/kg
10. The volume of consumable liquid in pregnancy has to be:
A. increased
B. decreased
CHAPTER 13. MECHANISM OF LABOR IN different types of CEPHALIC PRESENTATIONS
Cephalic presentation may be divided into flexed and deflexed presentation.
Flexed presentations
Flexed presentation is normal; it is the commonest presentation with a normal attitude of the fetus.
Attitude: the relation of different parts of fetus to each other is called attitude of the fetus. Attitude of flexion is normal: the head, trunk and limbs of the fetus are flexed in all joints and make up an ovoid form that corresponds approximately to the shape of the uterus. The flexion attitude is modified by the amount of liquor amnii and the muscular tension of the uterus and abdominal wall. There may be extension of the head (deflexed presentations: vertex, brow and face, according to the degree of extension). The legs may become extended in breech presentation. The course of labor in such circumstances may be modified accordingly.
Mechanism of Labor in Occipito-Anterior Presentation
It is the most typical, normal type of labor.
Occipito-anterior presentation means that the lie of the fetus is longitudinal, position is left or right, type of position is anterior, i. e. fetal back is to anterior wall of the uterus.
Broadly speaking, the mechanism of labor is as follows: in passage the head (and the trunk) makes three movements — engagement or entry into the pelvis, rotation or adaptation to the shape of the pelvis, and disengagement or exit from the pelvis.
In normal labor, the head enters the pelvic brim more commonly through the available transverse diameter (70%) and to a lesser extent through one of the oblique diameters. Thus, transverse diameter of the inlet becomes the diameter of engagement. In normal labor, the sagittal suture often strictly corresponds to the available transverse diameter of the inlet. It is called synclitism. But sometimes there may be physiologic short-term asynclitism, when the sagittal suture does not strictly correspond to the transverse diameter of the inlet. Instead, it is either deflected anteriorly towards the symphysis pubis or posteriorly towards the sacral promontory. When the sagittal suture lies anteriorly, the posterior parietal bone becomes the leading presenting part and is called posterior parietal presentation (Litzmann’s asynclitism, or posterior asynclitism) (Fig. 103).
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Fig. 103. Posterior asinklitism (posterior parietal presentation, Litzman’ asinklitism)
This is more frequently found in primigravidae because of good uterine tone and a tight abdominal wall. If the sagittal suture lies more posteriorly with the result that the anterior parietal bone becomes the leading presenting part, it is called anterior parietal presentation (anterior asynclitism, or Negele’s asynclitism) (Fig. 104).
Fig. 104. Anterior parietal presentation (anterior asinklitism, or Negele’s asinklitism).
It is more commonly found in multiparae. Short-term asynclitism may occur in normal labor: the posterior parietal bone hangs over the inlet with the sagittal suture directed downwards and forwards. In time the molding (configuration) of the head happens, and the anterior parietal bone descends behind the symphysis in a downward and backward direction following a curved axis of descent.
The long–term asynclitism usually occurs in pathological labor, for example, in labor with contracted pelvis.
It is necessary to know that the descent of the fetal head is a continuous movement. It is slow or insignificant in the first stage, but pronounced in the second stage. It is completed with the fetus delivery. In primigravidae, with prior engagement of the head, there is practically no descent in the first stage, while in multiparae the descent starts with engagement.
The principal moments of mechanism of normal labor are as follows:
The 1st moment is flexion of the head. When the descending head meets with resistance of both cervix and walls of the pelvis, flexion of the fetal head normally occurs.
Flexion is explained by the two arms lever theory: the fulcrum is represented by the atlas to occipital joint of the head, the short arm extends from the condyles to the occipital protuberance and the long arm extends from condyles to the chin. When the ordinary law of mechanics encounters resistance, the short arm descends and the long arm ascends in flexion of the head. As a result:
The chin is brought into close contact with the fetal breast.
The mechanical gain in flexion is that instead of an occipitofrontal diameter of 11 cm and a circumference of 35 cm, the suboccipitobregmatic extent with a diameter of 9–9. 5 cm and a circumference of 31 cm is presented to the birth canal.
Thus, in case of labor in occipito-anterior presentation there is suboccipitobregmatic diameter of the head (syn.: small oblique diameter) named engaging diameter of the head.
The posterior (or smaller) fontanelle is a point, which comes in relation with any planes of the pelvis earlier than other points; it is the first point, which is delivered through the vulva. It is called denominator (syn: a leading point) (Fig. 105).
The 2nd moment is internal rotation of the head. It is a movement of great importance without which there will be no further descent. This movement is not accomplished until the head has reached the level of the ischial spines (the 3rd pelvic plane — obstetrical outlet). The head descends into the birth canal and rotates simultaneously on its longitudinal axis so that the occiput (the posterior fontanelle) from its original position turns anteriorly (towards the symphysis pubis), while the sinciput (the anterior fontanelle) rotates posteriorly (towards the sacrum). At the beginning of this movement the sagittal suture is aligned with one of the oblique diameters. At the end of this movement (at the outlet of the pelvis) the sagittal suture of the head is parallel to the anteroposterior diameter of this plane of pelvis, the leading point (posterior fontanelle) is turned to the symphysis pubis. Such a position of the head means that the internal rotation of the head is completed. The internal rotation of the head with small fontanelle turned anteriorly is named correct internal rotation of the head.
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Fig. 105. Flexion of the head is the first moment of delivery in occipito-anterior presentation
The most probable theory which explains the internal rotation of the head is adjustment of the head diameters to the pelvic sizes (diameters): in every plane the fetus passes the largest diameter of the pelvis with the least or the most suitable diameter of the head. The transverse diameter is the largest in the pelvic inlet plane, so the head passes the largest diameter of the pelvic inlet with its least diameter (suboccipitobregmatic diameter). The largest diameter of the pelvic outlet plane is the anteroposterior diameter, so the head rotates accordingly from transverse diameter to the oblique and finally to the anteroposterior diameter (Fig. 106).
Fig. 106. The second moment is internal rotation of the head.
After internal rotation of the head, the further descent occurs until the subocciputal fossa lies underneath the pubic arch. At this stage, the biparietal diameter of the head stretches the vulval outlet with head recession after contraction; this act is called “crowning of the head”. When this process happens (continues) without any recession of the head, even after contraction is over, the act is called “disengagement of the head”.
The 3rd moment is extension of the head. When a strongly flexed head reaches the pelvic outlet, it meets with resistance of the pelvic floor muscles. Contractions of the uterine and abdominal muscles push the fetus in the direction of the sacral apex and coccyx. The muscles of the pelvic floor oppose that thrust of the fetal head in this direction and thus deflect its movement anteriorly towards the pudendal cleft. The resultant force causes the head to deflex when the posterior cranial fossa passes beyond the inferior margin of symphysis which acts as a fulcrum. The point of contact of subocciputal fossa and pubic arch is called the point of fixation (or hypomochlyon). The head revolves around the point of fixation (extension of the head), so the sinciput, the face and the chin gradually appear through the vulva. Thus the head is delivered.
So, the extension of the head occurs around the point of fixation (Fig. 107, 108).
Fig. 107. The third stage of labor in occiito-anterior presentation is extension of the head
Fig. 108. Delivery of the head due to extension (continuation).
The 4th moment is external rotation of the head. It is a rotation movement of the head visible externally due to internal rotation of the shoulders. In this movement, the occiput returns to the oblique position from which it started and then to the transverse position. This movement corresponds to the rotation of the fetal body, bringing the shoulders into an anteroposterior diameter of the pelvic outlet (Fig. 109).
Fig. 109. External rotation of the head (and internal rotation of shoulders)
The 5th moment is delivery of shoulders and trunk. After the shoulders are positioned in anteroposterior diameter of the outlet, further descent takes place until the anterior shoulder is fixed below the symphysis pubis. By a movement of lateral flexion of the spine the posterior shoulder rolls up over the perineum, after which the anterior shoulder comes from behind the pubis. The rest of the trunk is then expelled out by lateral flexion (Fig. 110).
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Fig. 110. Delivery of shoulders and trank.
Summary of mechanism of labor in occipito-anterior presentation:
Diameter of engagement is a transverse diameter of the pelvic inlet.
Engaging diameter of the head is suboccipitobregmatic (9. 5 cm) (small oblique diameter).
A leading point (denominator) is a smaller (posterior) fontanelle.
The point of fixation is suboccupital fossa.
The 1st moment is the flexion of the head.
The 2nd moment is a correct internal rotation of the head with occiput anteriorly.
The 3rd moment is delivery of the head by extension.
The 4th moment is external rotation of the head and internal rotation of the shoulders.
The 5th moment is delivery of the shoulders by lateral flexion and expulsion of the trunk.
Mechanism of Labor in Occipito-Posterior Presentation
Occipito-posterior positions are encountered in about 25% of all vertex presentations. In this case the lie of the fetus is longitudinal, attitude of the fetus is flexion, and the position is left or right, but type of position is posterior. Thus, one can find a small fontanelle towards the maternal sacrum by vaginal examination. During the second stage of labor the great majority of posterior types of position become converted into anterior by the forward rotation (by 135 degrees) of the occiput. This is the normal mechanism which occurs in about 80-90% of occipito–posterior cases. In the remainder the mechanism of labor is posterior, and the duration of labor is longer than that in occipito-anterior presentation, but it is a type of physiological mechanism.
The 1st moment is flexion of the head. The head is flexed and begins to engage to the inlet with its suboccipito-frontal diameter (10-10. 5 cm), while the sagittal suture is on the transverse diameter of the inlet. Denominator is a midpoint between a big and small fontanelle. There may be short-term asynclitism because of the lateral inclination of the head (sacral rotation).
The 2nd moment is internal rotation of the occiput posteriorly (small fontanelle towards the sacral promontory).
After the internal rotation of the head which usually takes place with the head occupying the 3rd, may be the 4th plane of the pelvis, descending of the head continues. Then the crowning of the head occurs. The first point born is denominator; then the surrounding areas are born. When the point of fixation is born, the 3rd moment of labor starts.
The 3rd moment is flexion of the head which occurs after the anterior margin of the haired part of the forehead lies underneath the pubic arch (it is the first point of fixation).
The head begins to revolve around the point of fixation (so flexion of the head begins). The successive parts of the fetal head to be born through the stretched vulval outlet are forehead (brow), vertex, posterior (small) fontanelle.
The 4th moment is extension of the head. During this moment the subocciputal fossa lies in direct contact with the anterior margin of the perineum. The subocciputal fossa is the second point of fixation; then the head begins to revolve around this point of fixation and the head extension occurs. The successive parts to be born are: face and chin. Thus the delivery of the head is completed.
The 5th moment is external rotation of the head and internal rotation of the shoulders.
The 6th moment is delivery of the shoulders and trunk by lateral flexion.
Summary of mechanism of labor in occipito-posterior presentation:
Diameter of engagement is a transverse diameter of the inlet (13-13. 5cm).
Engaging diameter of the head is suboccipito-frontal (10-10. 5cm).
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Denominator is a midpoint between a big and small fontanelle.
There are two points of fixation on the head: the 1st is the anterior margin of the haired part of the forehead, the 2nd is the suboccipital fossa.
The 1st moment is flexion.
The 2nd moment is internal rotation of the head with occiput posteriorly.
The 3rd moment is flexion (delivery of brow, vertex and small fontanelle).
The 4th moment is extension of the head.
The 5th moment is external rotation of the head and internal rotation of the shoulders.
The 6th moment is delivery of the shoulders and trunk by lateral flexion.
Deflexed cephalic presentations - malpresentations
To these the fetal attitude with extended head refers, which may have 3 degrees:
The 1st is the vertex presentation
The 2nd is the brow presentation
The 3rd is the face presentation.
Etiology of extension
Maternal factors include the following:
• Decreased tone of myometrium;
• Dyscoordinated labor pains;
• Decreased tone of muscles of the pelvic floor;
• Multiparity with pendulous abdomen;
• Contracted pelvis.
Fetal factors are as follows:
• Big fetus or immature fetus;
• Congenital malformation (the commonest one is anencephaly);
• Congenital goitre;
• Multiple twist of the cord round the neck of fetus;
• An increased tone of the neck extensors.
Mechanism of Labor in Vertex Presentation
The diagnosis during the 1st stage of labor depends on:
• ultrasound examination;
• internal (bimanual) examination: one can find a big (anterior) fontanelle and a small (posterior) one together when the cervix is rather opened.
The 1st moment is deflexion of the head, so the engaging diameter of the head is occipito-frontal (12 cm). The sagittal suture of the head is in transverse diameter of the pelvic inlet. Denominator is an anterior fontanelle (Fig. 114).
Fig. 114. Vertex presentation. The first moment: the head passes the pelvic cavity with it’s antero-posterior diameter, due to moderate extension.
The 2nd moment is internal rotation of the head with anterior fontanelle towards the symphysis pubis. On the pelvic floor the fetus head is in the antero-posterior diameter of the 4th plane (anatomical outlet) of the pelvis, the forehead is towards the symphysis pubis, the occiput is towards the sacrum promontory (Fig. 115).
Fig. 115. The internal rotation of the head in vertex presentation (forehead toward the symphysis pubis)
The 3rd moment is flexion of the head around the hypomochlion (around the point of fixation). There are two points of fixation in this mechnism of labor.
Due to descending of the head and crowning of the anterior fontanelle, glabella (1st point of fixation) is fixed to the lower margin of the pubic arch and the fetus head begins to revolve around this point of fixation. This is called flexion of the head on the pelvic floor, which leads to vertex delivery (vertex crowning) (Fig. 116).
Fig. 116. Vertex presentation. The 3rd moment is flexion of the head around the hypomochlion.
The 4th moment is extension of the head.
Occiput is fixed to the perineum and the head begins to revolve around this point of fixation, thus the head will extend. So the face and the chin are born.
The 5th moment is external rotation of the head and internal rotation of the shoulders and trunk (restitution).
The 6th moment is delivery of the shoulders and trunk (expulsion).
Summary of mechanism of labor in vertex presentation:
Diameter of engagement is a transverse diameter of the inlet (13-13. 5 cm).
The engaging diameter of the head is occipito-frontal (11. 5-12 cm).
The leading point (denominator) is anterior fontanelle.
There are two points of fixation on the head: the 1st is glabella, the 2nd is occiput.
Moments of biomechanism are:
• extension of the head,
• internal rotation of the head,
• flexion of the head on the pelvic floor,
• extension of the head,
• external rotation of the head and internal rotation of the shoulders,
• lateral flexion of the trunk.
Clinical Significance
Vertex presentation is an abnormal one. The delivery of a healthy newborn is impossible when the sizes of maternal pelvis and fetus head are normal (correspond to each other).
The main complications are: hemorrhages, fetus asphyxia, maternal and perinatal traumatism, intrauterine death of the fetus.
Cesarean section should be done to prevent complications in case of term delivery.
Mechanism of Labor in Brow Presentation
The diagnosis during the 1st stage of labor depends on:
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• Internal (vaginal) examination: one can find the forehead, frontal suture, root of nose (glabella), superciliary arches and anterior margin of a large fontanelle when the cervix is rather opened.
• Ultrasound examination.
The 1st moment is extension of the head. The engaging diameter of the head is occipitomental (13. 5 — the largest diameter of the head). (Fig. 117)
Fig. 117. The engaging diameter of the head in brow presentation is occipito-mental diameter.
The leading point (denominator) is a forehead. The frontal suture lies in the transverse diameter of the pelvic inlet.
The 2nd moment is internal rotation of the head with brow towards the symphysis pubis and a small fontanelle to the sacrum.
The 3rd moment is flexion of the head. Maxilla is fixed to the inferior margin of the pubic arch which leads to the flexion of the head (because of revolving around the point of fixation).
The 4th moment is extension of the head. Suboccipital region is fixed to the perineum and there is extension of the head.
The 5th moment is external rotation of the head and internal rotation of the shoulders.
The 6th moment is delivery of the shoulders (first posterior, then anterior) due to the fixation of the anterior shoulder to the pubic arch and lateral flexion of the trunk. Then there is expulsion of the trunk.
Summary of mechanism of labor in brow presentation:
Diameter of engagement is a transverse diameter of the inlet (13-13. 5 cm).
The engaging diameter of the head is an occipitomental diameter (13. 5).
The leading point (denominator) is a brow.
There are two points of fixation on the head: the 1st is maxilla, the 2nd is a suboccipital region.
Moments of biomechanism are:
• extension of the head,
• internal rotation of the head,
• flexion of the head on the pelvic floor,
• extension of the head,
• external rotation of the head and internal rotation of the shoulders,
• lateral flexion of the trunk.
Clinical significance
The brow presentation is abnormal.
Delivery in this presentation is impossible, except for premature labor.
Brow presentation is an indication for cesarean section to prevent fetus death.
Mechanism of Labor in Face Presentation
The diagnosis during the 1st stage of labor depends on:
• External palpation: one can find a furrow between the head and the trunk, which occurs due to significant extension of the head,
• Internal (vaginal) examination: one can find the chin, mouth, nose when the cervix is rather opened.
• Ultrasound examination helps to ascertain the face presentation.
The 1st moment is extension of the head (to a maximum degree). Thus, diameter of engagement is transverse or one of the oblique diameters of the inlet plane.
The engaging diameter of the head is a submentobregmatic diameter (9. 5 cm).
Denominator is the chin (Fig. 118)
Fig. 118. Face presentation: the first moment of delivery.
The 2nd moment is internal rotation of the head with the chin towards the symphysis pubis and a small fontanelle to the sacrum (Fig. 119)
Fig. 119 Face presentation: The 2nd moment is internal rotation of the head
The 3rd moment is flexion of the head. When the head descends to the pelvic floor and denominator is delivered, the sublingual area is fixed to the lower margin of symphysis pubis and the head begins to revolve around the point of fixation, it means flexion of the head. It is delivery of the brow, vertex, and occiput (Fig. 120).
Fig. 120. The 3rd moment is flexion of the head
The 4th moment is external rotation of the head and internal rotation of the shoulders.
The 5th moment is delivery of the shoulders (first posterior, then anterior) due to fixation of the anterior shoulder to the pubic arch and lateral flexion of the trunk. Then there is expulsion of the trunk.
Summary of mechanism of labor in face presentation:
Diameter of engagement is a transverse diameter of the pelvic inlet (13-13. 5 cm), or one of the oblique diameters.
The engaging diameter of the head is a vertical diameter (9. 5-10 cm).
The leading point (denominator) is the chin.
The only point of fixation on the head is the sublingual area.
Moments of biomechanism are:
• extension of the head,
• internal rotation of the head,
• flexion of the head on the pelvic floor,
• external rotation of the head and internal rotation of the shoulders,
• lateral flexion of the trunk.
Clinical significance
This type of labor is abnormal. A lot of complications occur during this type of labor: injuries of the fetus, premature rupture of the water membranes, asphyxia, intrauterine death of the fetus, etc.
The posterior type of position of face presentation (chin towards the sacrum) means impossibility of spontaneous labor.
Self Test
1. Which is the first moment of labor mechanism in occipito-anterior presentation?
A. the internal rotation of the head
B. deflexion of the head
C. flexion of the head
D. fixation of the head in the pelvic inlet
E. the external rotation of the head
2. Which is the second moment of labor mechanism in occipito-anterior presentation?
A. flexion of the head
B. deflexion of the head
C. the internal rotation of the head
D. the internal rotation of the shoulders
E. the external rotation of the head
3. Which is the third moment of labor mechanism in occipito-anterior presentation?
A. flexion of the head
B. fixation of the head under symphysis pubis
C. the internal rotation of the shoulders and external rotation of the head
D. extension of the head
E. the internal rotation of the head
4. Which is the first moment of labor mechanism in brow presentation?
A. deflexion of the head
B. flexion of the head
C. the internal rotation of the head
D. revolving of the head around the point of fixation
5. What is a denominator in occipito-anterior presentation?
A. anterior fontanelle
B. posterior fontanelle
C. brow
D. suboccipital fossa
E. midpoint between the anterior and posterior fontanelle
6. What is the point of fixation in occipito-anterior presentation?
A. small fontanelle
B. anterior fontanelle
C. suboccipital fossa
D. the anterior margin of the haired part of the head
E. nose
7. The engaging diameter of the head in face presentation is a:
A. submentobregmatic diameter,
B. occipitofrontal diameter
C. occipitobregmatic diameter
D. occipitomental diameter.
E. biparietal diameter
8. What is a denominator in a brow presentation?
A. large fontanelle
B. brow
C. chin.
D. small fontanelle
E. sagittal suture
9. Which of the following is more preferable for patients with brow presentation of the fetus?
A. normal ways of delivery
B. planned cesarean section
10. A deflexed head presentation is:
A. a variant of norm
B. a pathological type of presentation
CHAPTER 14. Physiology of LABOR AND DELIVERY
Theories of Labor Causes
1. Prostaglandin release is one of the most important factors in the spontaneous onset of labor. Prostaglandins are known to cause the uterine contraction at any term of pregnancy. Prostaglandin (Pg) administered both intravenously and vaginally induces uterine contraction.
One of the precursors of prostaglandins is nonesterified arachidonic acid. The level of nonesterified arachidonic acid in amniotic fluid increases before labor due to action of phospholipase which releases arachidonic acid from its esterified form in the fetal membranes. The esterified form of arachidonic acid is thought to be stored in the fetal membranes. Prostaglandin synthetase is found in fetal membranes and decidua vera, both of which produce prostaglandins. So, before labors the level of Pg, especially PgE2 and PgF2ά increases.
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