Vertex presentation and mechanism of labor

Lesson 1. Vertex presentation and mechanism of labor

1. Definition:

• Vertex presentation: Vertex presentation is a fetal presentation where the fetal head presents first, with the posterior fontanelle (the lambda) as the landmark. The fetal head is flexed, with the occiput (the back of the head) fitting into the brim of the pelvis. The biparietal diameter is the largest diameter of the presenting part.

2. Mechanism of labor:

• Mechanism of labor in vertex presentation: This refers to the series of movements that the fetal head undergoes to pass through the maternal birth canal during labor. This mechanism is divided into 4 stages:

• Engagement: The occipito-frontal diameter enters the pelvic inlet.

• Descent: The fetal head moves down through the pelvic inlet, through the midpelvis, and into the pelvic outlet.

• Flexion: The fetal head flexes further, so that the occiput is directed posteriorly, and the anterior fontanelle is directed anteriorly, enabling the head to pass through the pelvic outlet.

• Extension: The fetal head extends as it passes through the pelvic outlet, with the chin coming last.

3. Factors affecting the mechanism of labor:

• Pelvis: The size and shape of the maternal pelvis have a significant impact on the mechanism of labor in vertex presentation.

• Fetus: The size and position of the fetus also influence the mechanism of labor.

• Uterine contractions: Uterine contractions help to push the fetus down.

4. Clinical signs for diagnosing vertex presentation:

• Vaginal examination:

• The posterior fontanelle can be palpated, allowing the determination of the fetal presentation.

• The two parietal bones (occipital and frontal bones) can be felt.

• External examination:

• The occipital bone can be felt in the posterior part of the pelvis.

• The frontal bone can be felt in the anterior part of the pelvis.

• Both parietal bones can be felt within the vagina.

5. Points to note during labor with vertex presentation:

• Monitoring and observation: Monitor the fetal heart rate, cervical dilation, uterine contractions, the descent of the presenting part, the descent of the presenting part, the presence of a prolapsed cord, and the presence of a Bandl’s ring.

• Delivery techniques: Master the techniques of delivering a vertex presentation, including:

• Guiding the mother to push effectively.

• Keeping the fetal head flexed, preventing the head from extending excessively.

• Intervening promptly in case of emergencies such as prolapsed cord, Bandl’s ring, cephalopelvic disproportion, etc.

Lesson 2. Quiz

Below are questions and detailed answers to the quiz:

302. Which of the following is the correct definition of engagement in vertex presentation?

• A. When the presenting part enters the pelvic inlet.

• B. When the presenting part descends to the level of the ischial spines.

• C. When the biparietal diameter of the fetal head passes through the pelvic inlet.

• D. When the biparietal diameter of the fetal head is level with the ischial spines.

Answer: C

Explanation:

• Engagement occurs when the largest diameter of the presenting part (the biparietal diameter) passes through the pelvic inlet.

303. Which of the following statements best describes the significance of the engagement test?

• A. It is a test to evaluate whether there is cephalopelvic disproportion.

• B. It is used to assess whether the fetus can be delivered vaginally.

• C. It is a test applied in cases of cephalopelvic disproportion.

• D. It is a test to evaluate whether the presenting part can pass through the pelvic inlet in cases of suspected cephalopelvic disproportion.

Answer: D

Explanation:

• The engagement test is performed to assess the ability of the presenting part to pass through the pelvic inlet, which helps in early detection of cephalopelvic disproportion and timely interventions.

304. Under which of the following circumstances should the engagement test be stopped?

• A. Frequent contractions.

• B. Fetal bradycardia.

• C. Prolapsed cord.

• D. Bandl’s ring.

Answer: C

Explanation:

• Prolapsed cord is a serious condition that can lead to fetal compromise, so the engagement test should be stopped immediately to manage the situation.

305. Which of the following factors should be considered when assessing the results of the engagement test?

• A. Cervical dilation.

• B. Level of engagement.

• C. Uterine contractions.

• D. Fetal heart rate.

Answer: B

Explanation:

• The level of engagement is the primary factor for assessing the results of the engagement test.

306. The mechanism of labor in vertex presentation is presented in the following order:

• A. Breech, head, and body.

• B. Body, head, and breech.

• C. Head, shoulders, and breech.

• D. Head, breech, and body.

Answer: C

Explanation:

• The mechanism of labor in vertex presentation occurs in this order: Head, shoulders, and breech.

307. When the head of the vertex presentation (occiput anterior) is delivered, which diameter of the maternal pelvis does the presenting part pass through?

• A. Right oblique diameter of the pelvic inlet.

• B. Left oblique diameter of the pelvic inlet.

• C. Transverse diameter of the pelvic inlet.

• D. Anteroposterior diameter of the pelvic inlet.

Answer: B

Explanation:

• In occiput anterior presentation, the fetal head engages through the left oblique diameter of the pelvic inlet.

308. During the delivery of the shoulders, the bisacromial diameter passes through which diameter of the maternal pelvis?

• A. Right oblique diameter of the pelvic inlet.

• B. Left oblique diameter of the pelvic inlet.

• C. Transverse diameter of the pelvic inlet.

• D. Anteroposterior diameter of the pelvic inlet.

Answer: A

Explanation:

• During shoulder delivery, the bisacromial diameter passes through the right oblique diameter of the pelvic inlet.

309. During the delivery of the head, which diameter of the maternal pelvis does the presenting part pass through?

• A. Left oblique diameter of the pelvic outlet.

• B. Right oblique diameter of the pelvic outlet.

• C. Transverse diameter of the pelvic outlet.

• D. Anteroposterior diameter of the pelvic outlet.

Answer: D

Explanation:

• During the delivery of the head, the presenting part passes through the anteroposterior diameter of the pelvic outlet.

310. If the posterior fontanelle is located at the 2 o’clock position, the presentation is:

• A. Left occipitoposterior

• B. Right occipitoposterior

• C. Left occipitoanterior

• D. Right occipitoanterior

Answer: C

Explanation:

• The posterior fontanelle at the 2 o’clock position is characteristic of a left occipitoanterior presentation.

311. If the posterior fontanelle is located at the 7 o’clock position, the presentation is:

• A. Right occipitoanterior

• B. Left occipitoanterior

• C. Left occipitoposterior

• D. Right occipitoposterior

Answer: D

Explanation:

• The posterior fontanelle at the 7 o’clock position is characteristic of a right occipitoposterior presentation.

312. If the posterior fontanelle is located at the 5 o’clock position, the presentation is:

• A. Right occipitoposterior

• B. Left occipitoposterior

• C. Left occipitoanterior

• D. Right occipitoanterior

Answer: B

Explanation:

• The posterior fontanelle at the 5 o’clock position is characteristic of a left occipitoposterior presentation.

313. If the posterior fontanelle is located at the 11 o’clock position, the presentation is:

• A. Right occipitoanterior

• B. Right occipitoposterior

• C. Left occipitoanterior

• D. Left occipitoposterior

Answer: A

Explanation:

• The posterior fontanelle at the 11 o’clock position is characteristic of a right occipitoanterior presentation.

314. Which part of the vertex presentation is used to diagnose the relationship with the maternal pelvis?

• A. Chin

• B. Shoulder

• C. Posterior fontanelle

• D. Anterior fontanelle

Answer: C

Explanation:

• The posterior fontanelle is the landmark of the vertex presentation. Its location helps in determining the presentation and its relation to the maternal pelvis.

315. Landmark of the vertex presentation:

• A. Anterior fontanelle

• B. Posterior fontanelle

• C. Tip of the nose

• D. Chin

Answer: B

Explanation:

• The posterior fontanelle is the landmark of the vertex presentation.

316. How many diameters of the greater pelvis (false pelvis) are there?

• A. The greater pelvis is not related to the lesser pelvis and therefore does not have any bearing on the mechanism of labor.

• B. The greater pelvis has 3 transverse diameters and 2 anteroposterior diameters.

• C. The 2 anteroposterior diameters of the greater pelvis are the anteroposterior diameter of the pelvic inlet and the anteroposterior diameter of the pelvic outlet.

• D. The greater pelvis has 3 transverse diameters and 1 anteroposterior diameter (the diagonal conjugate).

Answer: D

Explanation:

• The greater pelvis has 3 transverse diameters and 1 anteroposterior diameter (the diagonal conjugate).

317. Lesser pelvis: Which of the following is correct about the importance of the lesser pelvis during delivery?

• A. The lesser pelvis is important in the mechanism of labor and is divided into 2 planes: the pelvic inlet and the pelvic outlet.

• B. The pelvic inlet is the plane of delivery: anteriorly it passes through the superior margin of the symphysis pubis and posteriorly through the promontory of the sacrum.

• C. The pelvic outlet is the plane of delivery: anteriorly it passes through the inferior margin of the symphysis pubis and posteriorly through the tip of the sacrum.

• D. The most important diameter of the pelvic outlet is the intertuberous diameter, which is 10.5-11 cm.

Answer: C

Explanation:

• The pelvic outlet is the plane of delivery, anteriorly it passes through the inferior margin of the symphysis pubis and posteriorly through the tip of the sacrum.

318. In a left occipitoanterior vertex presentation, engagement occurs when:

• A. The occipito-frontal diameter presents before the pelvic inlet.

• B. The suboccipito-frontal diameter presents before the pelvic inlet.

• C. The suboccipito-bregmatic diameter coincides with the pelvic inlet plane.

• D. The suboccipito-bregmatic diameter is parallel to the left oblique diameter of the pelvic inlet.

Answer: C

Explanation:

• Engagement occurs when the suboccipito-bregmatic diameter coincides with the pelvic inlet plane.

319. Clinically, engagement is determined when:

• A. Externally, only the frontal bone can be felt above the symphysis pubis.

• B. Externally, only the occipital bone can be felt above the symphysis pubis.

• C. Both parietal bones are palpable within the vagina.

• D. Vaginal examination: two fingers can hardly reach the sacral promontory.

Answer: C

Explanation:

• Engagement is clinically determined when both parietal bones are palpable within the vagina.

320. Which stage of labor best describes the delivery of the shoulders in a left occipitoanterior vertex presentation?

• A. Engagement: After the bisacromial diameter (shoulder width) is reduced to pass through the pelvic inlet.

• B. Descent: The shoulders descend through the right oblique diameter to reach the pelvic outlet.

• C. Rotation: The shoulders rotate 45 degrees clockwise immediately after engagement.

• D. Expulsion: The anterior shoulder delivers first, followed by the posterior shoulder, assisted by the mother’s pushing efforts.

Answer: A

Explanation:

• The engagement stage is when the bisacromial diameter is reduced to pass through the pelvic inlet.

321. In the delivery technique for a left occipitoanterior vertex presentation, the head should be kept flexed until:

• A. The occiput is delivered and rotates to the left anterior position.

• B. After the episiotomy is performed.

• C. The entire occipital bone has emerged from the vulva.

• D. The occiput is pressed against the inferior margin of the symphysis pubis.

Answer: D

Explanation:

• The head should be kept flexed until the occiput is pressed against the inferior margin of the symphysis pubis to prevent the head from extending excessively.

322. A vertex presentation with poor flexion has which of the following signs:

• A. The head is mobile.

• B. The posterior fontanelle is palpable.

• C. Both fontanelles (posterior and anterior) are palpable.

• D. The anterior fontanelle is palpable.

Answer: C

Explanation:

• A vertex presentation with poor flexion has the sign of both fontanelles (posterior and anterior) being palpable.

323. Engagement is when the largest diameter of the presenting part passes through the plane of the:

• A. Pelvic inlet.

• B. Midpelvis.

• C. Pelvic outlet.

• D. Intertuberous diameter.

Answer: A

Explanation:

• Engagement occurs when the largest diameter of the presenting part (the biparietal diameter) passes through the pelvic inlet.

324. The plane of delivery is the plane that passes through the boundary of the:

• A. Pelvic inlet.

• B. Midpelvis.

• C. Pelvic outlet.

• D. Intertuberous diameter.

Answer: C

Explanation:

• The plane of delivery is the plane that passes through the boundary of the pelvic outlet.

325. Clinically, which diameter is used to assess the level of engagement of the vertex presentation?

• A. Intertuberous diameter.

• B. Intertrochanteric diameter.

• C. Intercristal diameter.

• D. Sacrococcygeal diameter.

Answer: C

Explanation:

• Clinically, the intercristal diameter is used to assess the level of engagement of the vertex presentation.

326. In a vertex presentation with asynclitism, the external examination will reveal the following signs EXCEPT:

• A. Limited mobility of the fetal head to the sides.

• B. Inability to palpate the occipital bone or the frontal bone.

• C. The fetal heart is heard over the symphysis pubis 7 cm away.

• D. A portion of the occipital bone and the frontal bone can be felt.

Answer: D

Explanation:

• In asynclitism, the external examination will reveal limited mobility of the fetal head to the sides, inability to palpate the occipital bone or the frontal bone, the fetal heart is heard over the symphysis pubis 7 cm away, and no portion of the occipital bone and the frontal bone can be felt.

327. If the posterior fontanelle is located at the 3 o’clock position, the presentation is:

• A. Left occipitoanterior

• B. Left occipitoposterior

• C. Left occipitotransverse

• D. Right occipitotransverse

Answer: C

Explanation:

• The posterior fontanelle at the 3 o’clock position is characteristic of a left occipitotransverse presentation.

328. In vertex presentation, symmetric engagement is when:

• A. Both parietal bones descend simultaneously.

• B. Both parietal bones descend at different times.

• C. The posterior parietal bone descends before the anterior parietal bone.

• D. The anterior parietal bone descends before the posterior parietal bone.

Answer: A

Explanation:

• Symmetric engagement is when both parietal bones descend simultaneously.

329. In the absence of cephalopelvic disproportion, which of the following presentations can be delivered in a primary care setting?

• A. Anterior fontanelle presentation.

• B. Transverse presentation.

• C. Face presentation with mentum posterior.

• D. Vertex presentation.

Answer: D

Explanation:

• Vertex presentation is the most common presentation and can be delivered in a primary care setting in the absence of cephalopelvic disproportion.

330. In a left occipitoanterior vertex presentation with a direct occiput delivery, how does the shoulder rotate during the delivery of the shoulders?

• A. 45 degrees clockwise.

• B. 45 degrees counterclockwise.

• C. 135 degrees clockwise.

• D. 135 degrees counterclockwise.

Answer: A

Explanation:

• In a left occipitoanterior vertex presentation with a direct occiput delivery, the shoulder rotates 45 degrees clockwise during the delivery of the shoulders.

331. In a right occipitoposterior vertex presentation, for a direct occiput delivery, how should the fetal head rotate?

• A. 45 degrees clockwise.

• B. 135 degrees clockwise.

• C. 45 degrees counterclockwise.

• D. 135 degrees counterclockwise.

Answer: B

Explanation:

• In a right occipitoposterior vertex presentation, the fetal head needs to rotate 135 degrees clockwise for a direct occiput delivery.

332. Each fetal part undergoes four stages of labor in the following order:

• A. Descent, engagement, rotation, expulsion.

• B. Engagement, descent, rotation, expulsion.

• C. Rotation, descent, engagement, expulsion.

• D. Descent, rotation, engagement, expulsion.

Answer: B

Explanation:

• Each fetal part undergoes four stages of labor in this order: Engagement, descent, rotation, expulsion.

333. The clinical sign that indicates a low level of engagement in a vertex presentation is:

• A. Both parietal bones are above the level of the ischial spines.

• B. Both parietal bones are at the level of the ischial spines.

• C. Both parietal bones are below the level of the ischial spines.

• D. Both parietal bones are palpable within the vagina.

Answer: C

Explanation:

• A low level of engagement in a vertex presentation is indicated when both parietal bones are below the level of the ischial spines.

334. In a well-flexed vertex presentation, the diameter of the presenting part is:

• A. Suboccipito-mental.

• B. Suboccipito-frontal.

• C. Suboccipito-bregmatic.

• D. Occipito-frontal.

Answer: C

Explanation:

• In a well-flexed vertex presentation, the diameter of the presenting part is the suboccipito-bregmatic diameter.

335. During labor, which presentation can be mistaken for vertex presentation during vaginal examination?

• A. Face presentation.

• B. Brow presentation.

• C. Anterior fontanelle presentation.

• D. Complete breech presentation.

Answer: C

Explanation:

• During labor, anterior fontanelle presentation can be mistaken for vertex presentation during vaginal examination.

336. The useful diameter of the pelvic inlet is:

• A. Sacro-pubic diameter.

• B. Diagonal conjugate.

• C. True conjugate.

• D. Sacro-coccygeal diameter.

Answer: B

Explanation:

• The useful diameter of the pelvic inlet is the diagonal conjugate.

337. The largest diameter of the fetal head is:

• A. Suboccipito-bregmatic.

• B. Biparietal.

• C. Suboccipito-frontal.

• D. Submento-vertical.

Answer: D

Explanation:

• The largest diameter of the fetal head is the submento-vertical diameter.

338. During the delivery of a vertex presentation, the head should be kept flexed until:

• A. The head descends to station +3.

• B. After the occipital bone of the fetal head has emerged from the vulva.

• C. The occiput of the fetal head is pressed against the inferior margin of the symphysis pubis.

• D. The entire head and face of the fetus have emerged from the vulva.

Answer: C

Explanation:

• During the delivery of a vertex presentation, the head should be kept flexed until the occiput of the fetal head is pressed against the inferior margin of the symphysis pubis.

339. To assess engagement in a vertex presentation, if the head is palpable when pressing the thumb into the labia majora, this is known as:

• A. Farabeuf’s maneuver.

• B. Piszkaczek’s maneuver.

• C. Hegar’s sign.

• D. Tarnier’s sign.

Answer: B

Explanation:

• Piszkaczek’s maneuver is the assessment of engagement when the head is palpable when pressing the thumb into the labia majora.

340. Episiotomy is performed when indicated and appropriate during the delivery of the head. The usual location of the episiotomy (for a right-handed delivery provider) is:

• A. 10 o’clock.

• B. 8 o’clock.

• C. 7 o’clock.

• D. 5 o’clock.

Answer: C

Explanation:

• The usual location of the episiotomy for a right-handed delivery provider is at the 7 o’clock position.

341. Which of the following is correct regarding important factors in the process of labor?

• A. Pelvis and fetus.

• B. Pelvis and uterine contractions.

• C. Uterine contractions and the mother’s pushing efforts.

• D. The three main factors: pelvis, fetus, and uterine contractions.

Answer: D

Explanation:

• The important factors in the process of labor are pelvis, fetus, and uterine contractions.

342. Vertex presentation is a common presentation in labor, accounting for approximately:

• A. 94%.

• B. 95%.

• C. 96%.

• D. 97%.

Answer: B

Explanation:

• Vertex presentation is the most common presentation in labor, accounting for approximately 95%.

343. During the delivery of the shoulders in a vertex presentation, the bisacromial diameter reduces to:

• A. 9 cm.

• B. 9.5 cm.

• C. 10 cm.

• D. 10.5 cm.

Answer: B

Explanation:

• The bisacromial diameter reduces to about 9.5 cm during the delivery of the shoulders in a vertex presentation.

344. The levels of engagement in a vertex presentation are classified into four levels:

• A. High floating, asynclitic, fixed, engaged.

• B. High floating, fixed, asynclitic, engaged.

• C. Asynclitic, fixed, high floating, engaged.

• D. Fixed, high floating, asynclitic, engaged.

Answer: A

Explanation:

• The levels of engagement in a vertex presentation are classified into four levels: High floating, asynclitic, fixed, engaged.

345. The transverse diameter of the pelvic inlet measures approximately:

• A. 13 cm.

• B. 12.5 cm.

• C. 11 cm.

• D. 10.5 cm.

Answer: B

Explanation:

• The transverse diameter of the pelvic inlet measures approximately 12.5 cm.

346. The average measurement of the transverse diameter of the midpelvis is:

• A. 8.5 cm.

• B. 9 cm.

• C. 10 cm.

• D. 10.5 cm.

Answer: B

Explanation:

• The average measurement of the transverse diameter of the midpelvis is 9 cm.

Note:

• This information is provided for educational and reference purposes.

• Diagnosis and treatment should be based on the expertise of a qualified medical professional.

• This article may not contain all relevant information and further consultation with reliable sources is recommended.

• During labor, close monitoring of the mother and fetus is essential, and prompt intervention is necessary in case of any complications.