presentation definition in obg

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StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

StatPearls [Internet].

Delivery, face and brow presentation.

Julija Makajeva ; Mohsina Ashraf .

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Last Update: January 9, 2023 .

• Continuing Education Activity

Face and brow presentation is a malpresentation during labor when the presenting part is either the face or, in the case of brow presentation, it is the area between the orbital ridge and the anterior fontanelle. This activity reviews the evaluation and management of these two presentations and explains the role of the interprofessional team in managing delivery safely for both the mother and the baby.

• Describe the mechanism of labor in the face and brow presentation.
• Summarize potential maternal and fetal complications during the face and brow presentations.
• Review different management approaches for the face and brow presentation.
• Outline some interprofessional strategies that will improve patient outcomes in delivery cases with face and brow presentation issues.
• Introduction

The term presentation describes the leading part of the fetus or the anatomical structure closest to the maternal pelvic inlet during labor. The presentation can roughly be divided into the following classifications: cephalic, breech, shoulder, and compound. Cephalic presentation is the most common and can be further subclassified as vertex, sinciput, brow, face, and chin. The most common presentation in term labor is the vertex, where the fetal neck is flexed to the chin, minimizing the head circumference.

Face presentation – an abnormal form of cephalic presentation where the presenting part is mentum. This typically occurs because of hyperextension of the neck and the occiput touching the fetal back. Incidence of face presentation is rare, accounting for approximately 1 in 600 of all presentations. [1] [2] [3]

In brow presentation, the neck is not extended as much as in face presentation, and the leading part is the area between the anterior fontanelle and the orbital ridges. Brow presentation is considered the rarest of all malpresentation with a prevalence of 1 in 500 to 1 in 4000 deliveries. [3]

Both face and brow presentations occur due to extension of the fetal neck instead of flexion; therefore, conditions that would lead to hyperextension or prevent flexion of the fetal neck can all contribute to face or brow presentation. These risk factors may be related to either the mother or the fetus. Maternal risk factors are preterm delivery, contracted maternal pelvis, platypelloid pelvis, multiparity, previous cesarean section, black race. Fetal risk factors include anencephaly, multiple loops of cord around the neck, masses of the neck, macrosomia, polyhydramnios. [2] [4] [5]

These malpresentations are usually diagnosed during the second stage of labor when performing a digital examination. It is possible to palpate orbital ridges, nose, malar eminences, mentum, mouth, gums, and chin in face presentation. Based on the position of the chin, face presentation can be further divided into mentum anterior, posterior, or transverse. In brow presentation, anterior fontanelle and face can be palpated except for the mouth and the chin. Brow presentation can then be further described based on the position of the anterior fontanelle as frontal anterior, posterior, or transverse.

Diagnosing the exact presentation can be challenging, and face presentation may be misdiagnosed as frank breech. To avoid any confusion, a bedside ultrasound scan can be performed. [6]  The ultrasound imaging can show a reduced angle between the occiput and the spine or, the chin is separated from the chest. However, ultrasound does not provide much predicting value in the outcome of the labor. [7]

• Anatomy and Physiology

Before discussing the mechanism of labor in the face or brow presentation, it is crucial to highlight some anatomical landmarks and their measurements. 

Planes and Diameters of the Pelvis

The three most important planes in the female pelvis are the pelvic inlet, mid pelvis, and pelvic outlet. 

Four diameters can describe the pelvic inlet: anteroposterior, transverse, and two obliques. Furthermore, based on the different landmarks on the pelvic inlet, there are three different anteroposterior diameters, named conjugates: true conjugate, obstetrical conjugate, and diagonal conjugate. Only the latter can be measured directly during the obstetric examination. The shortest of these three diameters is obstetrical conjugate, which measures approximately 10.5 cm and is a distance between the sacral promontory and 1 cm below the upper border of the symphysis pubis. This measurement is clinically significant as the fetal head must pass through this diameter during the engagement phase. The transverse diameter measures about 13.5cm and is the widest distance between the innominate line on both sides. 

The shortest distance in the mid pelvis is the interspinous diameter and usually is only about 10 cm. 

Fetal Skull Diameters

There are six distinguished longitudinal fetal skull diameters:

• Suboccipito-bregmatic: from the center of anterior fontanelle (bregma) to the occipital protuberance, measuring 9.5 cm. This is the presenting diameter in vertex presentation. 
• Suboccipito-frontal: from the anterior part of bregma to the occipital protuberance, measuring 10 cm 
• Occipito-frontal: from the root of the nose to the most prominent part of the occiput, measuring 11.5cm
• Submento-bregmatic: from the center of the bregma to the angle of the mandible, measuring 9.5 cm. This is the presenting diameter in face presentation where the neck is hyperextended. 
• Submento-vertical: from the midpoint between fontanelles and the angle of the mandible, measuring 11.5cm 
• Occipito-mental: from the midpoint between fontanelles and the tip of the chin, measuring 13.5 cm. It is the presenting diameter in brow presentation. 

Cardinal Movements of Normal Labor

• Neck flexion
• Internal rotation
• Extension (delivers head)
• External rotation (Restitution)
• Expulsion (delivery of anterior and posterior shoulders)

Some of the key movements are not possible in the face or brow presentations.  

Based on the information provided above, it is obvious that labor will be arrested in brow presentation unless it spontaneously changes to face or vertex, as the occipito-mental diameter of the fetal head is significantly wider than the smallest diameter of the female pelvis. Face presentation can, however, be delivered vaginally, and further mechanisms of face delivery will be explained in later sections.

• Indications

As mentioned previously, spontaneous vaginal delivery can be successful in face presentation. However, the main indication for vaginal delivery in such circumstances would be a maternal choice. It is crucial to have a thorough conversation with a mother, explaining the risks and benefits of vaginal delivery with face presentation and a cesarean section. Informed consent and creating a rapport with the mother is an essential aspect of safe and successful labor.

• Contraindications

Vaginal delivery of face presentation is contraindicated if the mentum is lying posteriorly or is in a transverse position. In such a scenario, the fetal brow is pressing against the maternal symphysis pubis, and the short fetal neck, which is already maximally extended, cannot span the surface of the maternal sacrum. In this position, the diameter of the head is larger than the maternal pelvis, and it cannot descend through the birth canal. Therefore the cesarean section is recommended as the safest mode of delivery for mentum posterior face presentations. 

Attempts to manually convert face presentation to vertex, manual or forceps rotation of the persistent posterior chin to anterior are contraindicated as they can be dangerous.

Persistent brow presentation itself is a contraindication for vaginal delivery unless the fetus is significantly small or the maternal pelvis is large.

Continuous electronic fetal heart rate monitoring is recommended for face and brow presentations, as heart rate abnormalities are common in these scenarios. One study found that only 14% of the cases with face presentation had no abnormal traces on the cardiotocograph. [8] It is advised to use external transducer devices to prevent damage to the eyes. When internal monitoring is inevitable, it is suggested to place monitoring devices on bony parts carefully. 

People who are usually involved in the delivery of face/ brow presentation are:

• Experienced midwife, preferably looking after laboring woman 1:1
• Senior obstetrician 
• Neonatal team - in case of need for resuscitation 
• Anesthetic team - to provide necessary pain control (e.g., epidural)
• Theatre team  - in case of failure to progress and an emergency cesarean section will be required.
• Preparation

No specific preparation is required for face or brow presentation. However, it is essential to discuss the labor options with the mother and birthing partner and inform members of the neonatal, anesthetic, and theatre co-ordinating teams.

• Technique or Treatment

Mechanism of Labor in Face Presentation

During contractions, the pressure exerted by the fundus of the uterus on the fetus and pressure of amniotic fluid initiate descent. During this descent, the fetal neck extends instead of flexing. The internal rotation determines the outcome of delivery, if the fetal chin rotates posteriorly, vaginal delivery would not be possible, and cesarean section is permitted. The approach towards mentum-posterior delivery should be individualized, as the cases are rare. Expectant management is acceptable in multiparous women with small fetuses, as a spontaneous mentum-anterior rotation can occur. However, there should be a low threshold for cesarean section in primigravida women or women with large fetuses.

When the fetal chin is rotated towards maternal symphysis pubis as described as mentum-anterior; in these cases further descend through the vaginal canal continues with approximately 73% cases deliver spontaneously. [9] Fetal mentum presses on the maternal symphysis pubis, and the head is delivered by flexion. The occiput is pointing towards the maternal back, and external rotation happens. Shoulders are delivered in the same manner as in vertex delivery.

Mechanism of Labor in Brow Presentation

As this presentation is considered unstable, it is usually converted into a face or an occiput presentation. Due to the cephalic diameter being wider than the maternal pelvis, the fetal head cannot engage; thus, brow delivery cannot take place. Unless the fetus is small or the pelvis is very wide, the prognosis for vaginal delivery is poor. With persistent brow presentation, a cesarean section is required for safe delivery.

• Complications

As the cesarean section is becoming a more accessible mode of delivery in malpresentations, the incidence of maternal and fetal morbidity and mortality during face presentation has dropped significantly. [10]

However, there are still some complications associated with the nature of labor in face presentation. Due to the fetal head position, it is more challenging for the head to engage in the birth canal and descend, resulting in prolonged labor.

Prolonged labor itself can provoke foetal distress and arrhythmias. If the labor arrests or signs of fetal distress appear on CTG, the recommended next step in management is an emergency cesarean section, which in itself carries a myriad of operative and post-operative complications.

Finally, due to the nature of the fetal position and prolonged duration of labor in face presentation, neonates develop significant edema of the skull and face. Swelling of the fetal airway may also be present, resulting in respiratory distress after birth and possible intubation.

• Clinical Significance

During vertex presentation, the fetal head flexes, bringing the chin to the chest, forming the smallest possible fetal head diameter, measuring approximately 9.5cm. With face and brow presentation, the neck hyperextends, resulting in greater cephalic diameters. As a result, the fetal head will engage later, and labor will progress more slowly. Failure to progress in labor is also more common in both presentations compared to vertex presentation.

Furthermore, when the fetal chin is in a posterior position, this prevents further flexion of the fetal neck, as browns are pressing on the symphysis pubis. As a result, descend through the birth canal is impossible. Such presentation is considered undeliverable vaginally and requires an emergency cesarean section.

Manual attempts to change face presentation to vertex, manual or forceps rotation to mentum anterior are considered dangerous and are discouraged.

• Enhancing Healthcare Team Outcomes

A multidisciplinary team of healthcare experts supports the woman and her child during labor and the perinatal period. For a face or brow presentation to be appropriately diagnosed, an experienced midwife and obstetrician must be involved in the vaginal examination and labor monitoring. As fetal anomalies, such as anencephaly or goiter, can contribute to face presentation, sonographers experienced in antenatal scanning should also be involved in the care. It is advised to inform the anesthetic and neonatal teams in advance of the possible need for emergency cesarean section and resuscitation of the neonate. [11] [12]

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Disclosure: Julija Makajeva declares no relevant financial relationships with ineligible companies.

Disclosure: Mohsina Ashraf declares no relevant financial relationships with ineligible companies.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

• Cite this Page Makajeva J, Ashraf M. Delivery, Face and Brow Presentation. [Updated 2023 Jan 9]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

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Fetal Presentation, Position, and Lie (Including Breech Presentation)

• Key Points |

Abnormal fetal lie or presentation may occur due to fetal size, fetal anomalies, uterine structural abnormalities, multiple gestation, or other factors. Diagnosis is by examination or ultrasonography. Management is with physical maneuvers to reposition the fetus, operative vaginal delivery , or cesarean delivery .

Terms that describe the fetus in relation to the uterus, cervix, and maternal pelvis are

Fetal presentation: Fetal part that overlies the maternal pelvic inlet; vertex (cephalic), face, brow, breech, shoulder, funic (umbilical cord), or compound (more than one part, eg, shoulder and hand)

Fetal position: Relation of the presenting part to an anatomic axis; for transverse presentation, occiput anterior, occiput posterior, occiput transverse

Fetal lie: Relation of the fetus to the long axis of the uterus; longitudinal, oblique, or transverse

Normal fetal lie is longitudinal, normal presentation is vertex, and occiput anterior is the most common position.

Abnormal fetal lie, presentation, or position may occur with

Fetopelvic disproportion (fetus too large for the pelvic inlet)

Fetal congenital anomalies

Uterine structural abnormalities (eg, fibroids, synechiae)

Multiple gestation

Several common types of abnormal lie or presentation are discussed here.

Transverse lie

Fetal position is transverse, with the fetal long axis oblique or perpendicular rather than parallel to the maternal long axis. Transverse lie is often accompanied by shoulder presentation, which requires cesarean delivery.

Breech presentation

There are several types of breech presentation.

Frank breech: The fetal hips are flexed, and the knees extended (pike position).

Complete breech: The fetus seems to be sitting with hips and knees flexed.

Single or double footling presentation: One or both legs are completely extended and present before the buttocks.

Types of breech presentations

Breech presentation makes delivery difficult ,primarily because the presenting part is a poor dilating wedge. Having a poor dilating wedge can lead to incomplete cervical dilation, because the presenting part is narrower than the head that follows. The head, which is the part with the largest diameter, can then be trapped during delivery.

Additionally, the trapped fetal head can compress the umbilical cord if the fetal umbilicus is visible at the introitus, particularly in primiparas whose pelvic tissues have not been dilated by previous deliveries. Umbilical cord compression may cause fetal hypoxemia.

Predisposing factors for breech presentation include

Preterm labor

Uterine abnormalities

Fetal anomalies

If delivery is vaginal, breech presentation may increase risk of

Umbilical cord prolapse

Birth trauma

Perinatal death

Face or brow presentation

In face presentation, the head is hyperextended, and position is designated by the position of the chin (mentum). When the chin is posterior, the head is less likely to rotate and less likely to deliver vaginally, necessitating cesarean delivery.

Brow presentation usually converts spontaneously to vertex or face presentation.

Occiput posterior position

The most common abnormal position is occiput posterior.

The fetal neck is usually somewhat deflexed; thus, a larger diameter of the head must pass through the pelvis.

Progress may arrest in the second phase of labor. Operative vaginal delivery or cesarean delivery is often required.

Position and Presentation of the Fetus

If a fetus is in the occiput posterior position, operative vaginal delivery or cesarean delivery is often required.

In breech presentation, the presenting part is a poor dilating wedge, which can cause the head to be trapped during delivery, often compressing the umbilical cord.

For breech presentation, usually do cesarean delivery at 39 weeks or during labor, but external cephalic version is sometimes successful before labor, usually at 37 or 38 weeks.

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Abnormal Fetal lie, Malpresentation and Malposition

Original Author(s): Anna Mcclune Last updated: 1st December 2018 Revisions: 12

• 1 Definitions
• 2 Risk Factors
• 3.2 Presentation
• 3.3 Position
• 4 Investigations
• 5.1 Abnormal Fetal Lie
• 5.2 Malpresentation
• 5.3 Malposition

The lie, presentation and position of a fetus are important during labour and delivery.

In this article, we will look at the risk factors, examination and management of abnormal fetal lie, malpresentation and malposition.

Definitions

• Longitudinal, transverse or oblique
• Cephalic vertex presentation is the most common and is considered the safest
• Other presentations include breech, shoulder, face and brow
• Usually the fetal head engages in the occipito-anterior position (the fetal occiput facing anteriorly) – this is ideal for birth
• Other positions include occipito-posterior and occipito-transverse.

Note: Breech presentation is the most common malpresentation, and is covered in detail here .

Fig 1 – The two most common fetal presentations: cephalic and breech.

Risk Factors

The risk factors for abnormal fetal lie, malpresentation and malposition include:

• Multiple pregnancy
• Uterine abnormalities (e.g fibroids, partial septate uterus)
• Fetal abnormalities
• Placenta praevia
• Primiparity

Identifying Fetal Lie, Presentation and Position

The fetal lie and presentation can usually be identified via abdominal examination. The fetal position is ascertained by vaginal examination.

For more information on the obstetric examination, see here .

• Face the patient’s head
• Place your hands on either side of the uterus and gently apply pressure; one side will feel fuller and firmer – this is the back, and fetal limbs may feel ‘knobbly’ on the opposite side

Presentation

• Palpate the lower uterus (above the symphysis pubis) with the fingers of both hands; the head feels hard and round (cephalic) and the bottom feels soft and triangular (breech)
• You may be able to gently push the fetal head from side to side

The fetal lie and presentation may not be possible to identify if the mother has a high BMI, if she has not emptied her bladder, if the fetus is small or if there is polyhydramnios .

During labour, vaginal examination is used to assess the position of the fetal head (in a cephalic vertex presentation). The landmarks of the fetal head, including the anterior and posterior fontanelles, indicate the position.

Fig 2 – Assessing fetal lie and presentation.

Investigations

Any suspected abnormal fetal lie or malpresentation should be confirmed by an ultrasound scan . This could also demonstrate predisposing uterine or fetal abnormalities.

Abnormal Fetal Lie

If the fetal lie is abnormal, an external cephalic version (ECV) can be attempted – ideally between 36 and 38 weeks gestation.

ECV is the manipulation of the fetus to a cephalic presentation through the maternal abdomen.

It has an approximate success rate of 50% in primiparous women and 60% in multiparous women. Only 8% of breech presentations will spontaneously revert to cephalic in primiparous women over 36 weeks gestation.

Complications of ECV are rare but include fetal distress , premature rupture of membranes, antepartum haemorrhage (APH) and placental abruption. The risk of an emergency caesarean section (C-section) within 24 hours is around 1 in 200.

ECV is contraindicated in women with a recent APH, ruptured membranes, uterine abnormalities or a previous C-section .

Fig 3 – External cephalic version.

Malpresentation

The management of malpresentation is dependent on the presentation.

• Breech – attempt ECV before labour, vaginal breech delivery or C-section
• Brow – a C-section is necessary
• If the chin is anterior (mento-anterior) a normal labour is possible; however, it is likely to be prolonged and there is an increased risk of a C-section being required
• If the chin is posterior (mento-posterior) then a C-section is necessary
• Shoulder – a C-section is necessary

Malposition

90% of malpositions spontaneously rotate to occipito-anterior as labour progresses. If the fetal head does not rotate, rotation and operative vaginal delivery can be attempted. Alternatively a C-section can be performed.

• Usually the fetal head engages in the occipito-anterior position (the fetal occiput facing anteriorly) - this is ideal for birth

If the fetal lie is abnormal, an external cephalic version (ECV) can be attempted - ideally between 36 and 38 weeks gestation.

• Breech - attempt ECV before labour, vaginal breech delivery or C-section

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RELATED TOPICS

INTRODUCTION

Diagnosis and management of face and brow presentations will be reviewed here. Other cephalic malpresentations are discussed separately. (See "Occiput posterior position" and "Occiput transverse position" .)

Prevalence  —  Face and brow presentation are uncommon. Their prevalences compared with other types of malpresentations are shown below [ 1-9 ]:

● Occiput posterior – 1/19 deliveries

● Breech – 1/33 deliveries

Presentation (Obstetrics)

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

• 2 Types of Presentations
• 4 References

Presentation in Obstetrics refers to the relationship between the leading fetal part and the pelvic inlet: cephalic, breech, or shoulder presentation. A malpresentation is an abnormal (non-vertex) presentation.

Types of Presentations

Thus the various presentations are:

• Vertex —commonest and associated with least complications
• Sinciput (forehead)
• Brow (Eye brows)
• Complete breech
• Footling breech
• Frank breech
• Child birth
• Fetal relations

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Fetal Presentation, Position, and Lie (Including Breech Presentation)

• Variations in Fetal Position and Presentation |

During pregnancy, the fetus can be positioned in many different ways inside the mother's uterus. The fetus may be head up or down or facing the mother's back or front. At first, the fetus can move around easily or shift position as the mother moves. Toward the end of the pregnancy the fetus is larger, has less room to move, and stays in one position. How the fetus is positioned has an important effect on delivery and, for certain positions, a cesarean delivery is necessary. There are medical terms that describe precisely how the fetus is positioned, and identifying the fetal position helps doctors to anticipate potential difficulties during labor and delivery.

Presentation refers to the part of the fetus’s body that leads the way out through the birth canal (called the presenting part). Usually, the head leads the way, but sometimes the buttocks (breech presentation), shoulder, or face leads the way.

Position refers to whether the fetus is facing backward (occiput anterior) or forward (occiput posterior). The occiput is a bone at the back of the baby's head. Therefore, facing backward is called occiput anterior (facing the mother’s back and facing down when the mother lies on her back). Facing forward is called occiput posterior (facing toward the mother's pubic bone and facing up when the mother lies on her back).

Lie refers to the angle of the fetus in relation to the mother and the uterus. Up-and-down (with the baby's spine parallel to mother's spine, called longitudinal) is normal, but sometimes the lie is sideways (transverse) or at an angle (oblique).

For these aspects of fetal positioning, the combination that is the most common, safest, and easiest for the mother to deliver is the following:

Head first (called vertex or cephalic presentation)

Facing backward (occiput anterior position)

Spine parallel to mother's spine (longitudinal lie)

Neck bent forward with chin tucked

Arms folded across the chest

If the fetus is in a different position, lie, or presentation, labor may be more difficult, and a normal vaginal delivery may not be possible.

Variations in fetal presentation, position, or lie may occur when

The fetus is too large for the mother's pelvis (fetopelvic disproportion).

The uterus is abnormally shaped or contains growths such as fibroids .

The fetus has a birth defect .

There is more than one fetus (multiple gestation).

Position and Presentation of the Fetus

Variations in fetal position and presentation.

Some variations in position and presentation that make delivery difficult occur frequently.

Occiput posterior position

In occiput posterior position (sometimes called sunny-side up), the fetus is head first (vertex presentation) but is facing forward (toward the mother's pubic bone—that is, facing up when the mother lies on her back). This is a very common position that is not abnormal, but it makes delivery more difficult than when the fetus is in the occiput anterior position (facing toward the mother's spine—that is facing down when the mother lies on her back).

When a fetus faces up, the neck is often straightened rather than bent,which requires more room for the head to pass through the birth canal. Delivery assisted by a vacuum device or forceps or cesarean delivery may be necessary.

Breech presentation

In breech presentation, the baby's buttocks or sometimes the feet are positioned to deliver first (before the head).

When delivered vaginally, babies that present buttocks first are more at risk of injury or even death than those that present head first.

The reason for the risks to babies in breech presentation is that the baby's hips and buttocks are not as wide as the head. Therefore, when the hips and buttocks pass through the cervix first, the passageway may not be wide enough for the head to pass through. In addition, when the head follows the buttocks, the neck may be bent slightly backwards. The neck being bent backward increases the width required for delivery as compared to when the head is angled forward with the chin tucked, which is the position that is easiest for delivery. Thus, the baby’s body may be delivered and then the head may get caught and not be able to pass through the birth canal. When the baby’s head is caught, this puts pressure on the umbilical cord in the birth canal, so that very little oxygen can reach the baby. Brain damage due to lack of oxygen is more common among breech babies than among those presenting head first.

In a first delivery, these problems may occur more frequently because a woman’s tissues have not been stretched by previous deliveries. Because of risk of injury or even death to the baby, cesarean delivery is preferred when the fetus is in breech presentation, unless the doctor is very experienced with and skilled at delivering breech babies or there is not an adequate facility or equipment to safely perform a cesarean delivery.

Breech presentation is more likely to occur in the following circumstances:

Labor starts too soon (preterm labor).

The uterus is abnormally shaped or contains abnormal growths such as fibroids .

Other presentations

In face presentation, the baby's neck arches back so that the face presents first rather than the top of the head.

In brow presentation, the neck is moderately arched so that the brow presents first.

Usually, fetuses do not stay in a face or brow presentation. These presentations often change to a vertex (top of the head) presentation before or during labor. If they do not, a cesarean delivery is usually recommended.

In transverse lie, the fetus lies horizontally across the birth canal and presents shoulder first. A cesarean delivery is done, unless the fetus is the second in a set of twins. In such a case, the fetus may be turned to be delivered through the vagina.

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Chapter 8:  Engagement, Synclitism, Asynclitism

Glenn D. Posner

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• SYNCLITISM AND ASYNCLITISM
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When the presenting part of the fetus is entirely out of the pelvis and is freely movable above the inlet, it is said to be floating ( Fig. 8-1A ).

When the presenting part has passed through the plane of the inlet but engagement has not occurred, it is said to be dipping ( Fig. 8-1B ).

By definition, engagement ( Fig. 8-1C ) has taken place when the widest diameter of the presenting part has passed through the inlet. In cephalic presentations, this diameter is the biparietal, between the parietal bosses. In breech presentation, it is the intertrochanteric.

FIGURE 8-1.

The process of engagement.

In most women, once the head is engaged, the bony presenting part (not the caput succedaneum) is at or nearly at the level of the ischial spines. Radiologic studies have shown that this relationship is not constant and that in women with deep pelves, the presenting part may be as much as 1 cm above the spines even though engagement has occurred.

The presence or absence of engagement is determined by abdominal or vaginal examination. In primigravidas, engagement usually takes place 2 to 3 weeks before term. In multiparas engagement, engagement may occur any time before or after the onset of labor. Engagement tells us that the pelvic inlet is adequate. It gives no information as to the midpelvis or the outlet. Although failure of engagement in a primigravida is an indication for careful examination to rule out disproportion, abnormal presentation, or some condition blocking the birth canal, it is no cause for alarm. The occurrence of engagement in normal cases is influenced by the tonus of the uterine and abdominal muscles.

Station is the relationship of the presenting part to an imaginary line drawn between the ischial spines ( Fig. 8-2 ). The location of the buttocks in breech presentations or the bony skull (not the caput succedaneum) in cephalic presentations at the level of the spines indicates that the station is zero. Above the spines, the station is −1, −2, and so forth, depending on how many centimeters above the spines the presenting part is. At spines −5, it is at the inlet. Below the spines, it is +1, +2, and so forth. There are various relationships between station and the progress of labor.

FIGURE 8-2.

Station of the presenting part.

In nulliparas entering labor with the fetal head well below the spines, further descent is often delayed until the cervix is fully dilated

In nulliparas beginning labor with the head deep in the pelvis, descent beyond the spines often takes place during the first stage of labor

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At the time the article was created Yuranga Weerakkody had no recorded disclosures.

At the time the article was last revised Joshua Yap had no financial relationships to ineligible companies to disclose.

• Funic presentation
• Cord (funic) presentation

A cord presentation (also known as a funic presentation or obligate cord presentation ) is a variation in the fetal presentation  where the umbilical cord points towards the internal cervical os or lower uterine segment.

It may be a transient phenomenon and is usually considered insignificant until ~32 weeks. It is concerning if it persists past that date, after which it is recommended that an underlying cause be sought and precautionary management implemented.

On this page:

Epidemiology, radiographic features, treatment and prognosis, differential diagnosis.

• Cases and figures

The estimated incidence is at ~4% of pregnancies.

Associations

Recognized associations include:

marginal cord insertion from the caudal end of a low-lying placenta

uterine fibroids

uterine adhesions

congenital uterine anomalies that may prevent the fetus from engaging well into the lower uterine segment

cephalopelvic disproportion

polyhydramnios

multifetal pregnancy

long umbilical cord

Color Doppler interrogation is extremely useful and shows cord between the fetal presenting part and the internal cervical os. However, unlike a vasa previa , the placental insertion is usually normal.

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As the complicating umbilical cord prolapse can lead to catastrophic consequences, most advocate an elective cesarean section delivery for persistent cord presentation in the third trimester 3 .

Complications

It can result in a higher rate of umbilical cord prolapse .

For the presence of umbilical cord vessels between the fetal presenting part and the internal cervical os on ultrasound consider:

vasa previa

• 1. Ezra Y, Strasberg SR, Farine D. Does cord presentation on ultrasound predict cord prolapse? Gynecol. Obstet. Invest. 2003;56 (1): 6-9. doi:10.1159/000072323 - Pubmed citation
• 2. Kinugasa M, Sato T, Tamura M et-al. Antepartum detection of cord presentation by transvaginal ultrasonography for term breech presentation: potential prediction and prevention of cord prolapse. J. Obstet. Gynaecol. Res. 2007;33 (5): 612-8. doi:10.1111/j.1447-0756.2007.00620.x - Pubmed citation
• 3. Raga F, Osborne N, Ballester MJ et-al. Color flow Doppler: a useful instrument in the diagnosis of funic presentation. J Natl Med Assoc. 1996;88 (2): 94-6. - Free text at pubmed - Pubmed citation
• 4. Bluth EI. Ultrasound, a practical approach to clinical problems. Thieme Publishing Group. (2008) ISBN:3131168323. Read it at Google Books - Find it at Amazon

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1.8: Obstetrics

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• Page ID 64957

• Stacey Grimm, Coleen Allee, Elaine Strachota, Laurie Zielinski, Traci Gotz, Micheal Randolph, and Heidi Belitz
• Nicolet College via Wisconsin Technical College System

Learning Objectives

• Identify the common processes in obstetrics
• Describe the specialty of obstetrics
• Spell the medical terms used in obstetrics and use correct abbreviations
• Identify the medical specialties associated with obstetrics
• Explore common complications and procedures related to obstetrics

Obstetric Word Parts

Click on prefixes, combining forms, and suffixes to reveal a list of word parts to memorize related to obstetrics., query \(\pageindex{1}\), introduction to obstetrics.

Obstetrics is a specialty that is concerned with the mother and fetus during pregnancy, childbirth and the immediate postpartum period. Obstetricians study obstetrics and gynecology and are referred to as OB/GYN Obstetrics and Gynecology.

Watch this video:

A YouTube element has been excluded from this version of the text. You can view it online here: https://pb.libretexts.org/med/?p=87

Media 8.1. R eproductive System, Part 4 – Pregnancy & Development: Crash Course A&P #43 [Online video]. Copyright 2015 by CrashCourse .

Obstetrics Medical Terms

Query \(\pageindex{2}\), fertilization.

Fertilization occurs when a sperm and an oocyte (egg) combine. Because each of these reproductive cells is a haploid cell containing half of the genetic material needed to form a human being, their combination forms a diploid cell. This new single cell is called a zygote.

Most of the time, a woman releases a single egg during an ovulation cycle.

• Two zygotes form, implant, and develop, resulting in the birth of dizygotic (or fraternal) twins . Because dizygotic twins develop from two eggs fertilized by two sperm, they are no more identical than siblings born at different times.
• Less common, one zygote can divide into two separate offspring during early development. This results in the birth of monozygotic (or identical) twins .

A full-term pregnancy lasts approximately 270 days (approximately 38.5 weeks) from conception to birth. Because it is easier to remember the first day of the last menstrual period (LMP) than to estimate the date of conception, obstetricians set the due date as 284 days (approximately 40.5 weeks) from the LMP. This assumes that conception occurred on day 14 of the woman’s cycle, which is usually a good approximation. The 40 weeks of an average pregnancy are usually discussed in terms of three trimesters, each approximately 13 weeks. During the second and third trimesters, the pre-pregnancy uterus is about the size of a fist and grows dramatically to contain the fetus, causing a number of anatomical changes in the mother.

The process of childbirth can be divided into three stages (see Figure 8.1):

• cervical dilation
• expulsion of the newborn
• after birth

For vaginal birth to occur, the cervix must dilate fully to 10 cm in diameter, wide enough to deliver the newborn’s head. The dilation stage is the longest stage of labor and typically takes 6-12 hours. However, it varies widely and may take minutes, hours, or days, depending in part on whether the mother has given birth before. In each subsequent labor, this stage tends to be shorter.

Concept Check

• How is a due date determined?
• Explain the difference between a monozygotic pregnancy and a dizygotic pregnancy .

Homeostasis in the Newborn: Apgar Score

In the minutes following birth, a newborn must undergo dramatic systemic changes to be able to survive outside the womb. An obstetrician, midwife, or nurse can estimate how well a newborn is doing by obtaining an Apgar score (Fig 8.2). The Apgar score was introduced in 1952 by the anesthesiologist Dr. Virginia Apgar as a method to assess the effects on the newborn of anesthesia given to the laboring mother. Healthcare providers now use it to assess the general well-being of the newborn, whether or not analgesics or anesthetics were used.

The technique for determining an Apgar score is quick and easy, painless for the newborn, and does not require any instruments except for a stethoscope. A convenient way to remember the five scoring criteria is to apply the mnemonic APGAR:

• A ppearance (skin color)
• P ulse (heart rate)
• G rimace (reflex)
• A ctivity (muscle tone)
• R espiration

Of the five Apgar criteria, heart rate and respiration are the most critical. Poor scores for either of these measurements may indicate the need for immediate medical attention to resuscitate or stabilize the newborn. In general, any score lower than 7 at the 5-minute mark indicates that medical assistance may be needed. A total score below 5 indicates an emergency situation. Normally, a newborn will get an intermediate score of 1 for some of the Apgar criteria and will progress to a 2 by the 5-minute assessment. Scores of 8 or above are normal.

Obstetrics Medical Terms not Easily Broken into Word Parts

Query \(\pageindex{3}\), obstetrics abbreviations, query \(\pageindex{4}\), medical terms in context, query \(\pageindex{5}\), procedures related to obstetrics, in vitro fertilization (ivf).

IVF, which stands for in vitro fertilization, is an assisted reproductive technology. In vitro, which in Latin translates to in glass, refers to a procedure that takes place outside of the body. There are many different indications for IVF. For example, a woman may produce normal eggs, but the eggs cannot reach the uterus because the uterine tubes are blocked or otherwise compromised. A man may have a low sperm count, low sperm motility, sperm with an unusually high percentage of morphological abnormalities, or sperm that are incapable of penetrating the zona pellucida of an egg. Figure 8.3 illustrates the steps involved in IVF.

Test Yourself

Query \(\pageindex{6}\).

[CrashCourse]. (2019, November 23). Reproductive System, Part 4 – Pregnancy & Development: Crash Course A&P #43 [Video]. YouTube. https://youtu.be/BtsSbZ85yiQ

Unless otherwise indicated, this chapter contains material adapted from Anatomy and Physiology (on OpenStax ), by Betts, et al. and is used under a a CC BY 4.0 international license . Download and access this book for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction .