Clinical: Labor and Delivery Flashcards
3 stages of labor
- Cervical stage
- Pelvic stage
- Placental stage
2 cervical changes during the first stage of labor
- Effacement of the cervix
- Dilatation of the cervix
Defnie effacement of the cervix
Shortening of the cervical canal into a paper-thin orifice
When does effacement occur?
As the muscle fibers near the internal os are pulled upward into the lower uterine segment
Define dilatation of the cervix
Gradual widening of the cervical os
Required cervical dilatation to allow the head of the average fetus at term to be able to pass
Approx 10 cm
When is the cervix completely dilated?
When the fetal head is able to descend past the remaining cervix
Define the pelvic stage of delivery
Passage of the fetus through the maternal pelvis and expulsion of the fetus. Begins with complete dilation of the cervix and ends when the infant is delivered
How long should the pelvic stage of labor last in a nulliparous person with or without regional anesthesia
With = less than 3 hours
Without = less than 2 hours
How long should the pelvic stage of labor last in a multiparous patient with or without regional anesthesia
Without = less than 1 hour
With = less than 2 hours
Define the third stage (placental) of labor
Separation and expulsion of the placenta. Begins with delivery of the infant and ends with the delivery of the placenta
4 proposed theories to explain the mechanism of labor
- Oxytocin stimulation
- Fetal cortisol levels
- Progesterone withdrawal
- Prostaglandin release
Describe the levels of oxytocin in maternal blood during labor
Early labor levels > onset of labor levels (no evidence of a sudden surge)
Explain how oxytocin may play a role in the spontaneous onset of labor
Oxytocin influence must rely on the presence of oxytocin receptors
- Receptors are found in the non-pregnant uterus
- 6-fold increase in receptors at 13 to 17 weeks’ gestations and an 80-fold increase at term
- Increased number of oxytocin receptors amplifies the biologic effect of oxytocin and contractions intensify
Give evidence as to how fetal cortisol levels may influence the spontaneous onset of labor
Disruption of hypothalamic-pituitary-adrenal axis or the absence of adrenal gland/function = prolonged gestation in humans and sheep
In sheep, infusion of cortisol or ACTH into a fetus with an intact adrenal gland causes premature labor, but not documentation of pre-labor surge in fetal cortisol to support this theory
Give evidence as to how progesterone withdrawal may cause labor
- Rabbits = withdrawal of P –> prompt labor
- Humans = no obvious decrease in maternal blood levels of P at term or in labor. However, P level at the placental site may decrease before onset of labor + increased E levels –> increased formation of gap junctions –> coupling of myometrial cells
2 specific prostaglandins believed to be involved in spontaneous onset of labor
PGF 2(alpha) and PGE2
Describe how prostaglandin release may cause labor
Normal processes of layer lead to inflammation –> increased prostaglandin synthesis. Production in myometrial tissue may contribute to effectiveness of myometrial contractions during labor and may soften cervix independent of uterine activity
3 components of labor
- Power - contractions
- Passenger - fetus
- Passage - pelvis
Describe early labor contractions
- Occur every 5-10 min
- Last for 30 - 45 sec
- 20 - 30 mm Hg in intensity
Describe late labor contractions
- Occur every 2 - 3 min
- Last for 50 - 70 sec
- 40 - 60 mm Hg pressure/intensity
5 aspects of the fetus to be aware of during labor
- Presentation
- Position
- Fetal lie
- Fetal attitude or posture
- Changes in the shape of the fetal head
Define presentation in terms of the fetus
Indicates that portion of the fetus that overlies the pelvic inlet
How to determine the presentation of the fetus
Inspection and palpation of the maternal abdomen (Leopold’s maneuvers)
4 types of fetal presentation
- Cephalic (95%)
- Breech (3.5%)
- Shoulder (0.4%)
- Face (0.3%)
3 types of cephalic presentation
- Vertex
- Face
- Brow
Define vertex cephalic presentation
Head is well flexed and the parietal bones are presenting
Define face cephalic presentation
Head is completely extended and face is presentin
Define brow cephalic presentation
Head is deflexed (or only partially extended)
Type of cephalic presentation that cannot deliver vaginally and why
Brow = largest antero-posterior diameter of the head is trying to megotiate through the maternal pelvis
3 types of breech presentation
- Frank breech
- Complete breech
- Incomplete or footling breech
Define frank breech presentaiton
Thighs flexed, legs extended over anterior aspect of abdomen
Define complete breech presentation
Thighs flexed, legs flexed
Define incomplete or footling breech presentation
Knees and feet, one or both, are lowest and presenting
Define the Position with regards to the fetus
Relation of the fetal presenting part to the maternal pelvis
4 markers for position of fetus
- Occiput for vertex presentation
- Sacrum for breech presentation
- Mentum (chin) for face presentation
- Acromion for sohulder presentation
5 different positions for the designated fetal bony point
Relative to the maternal pelvis:
- Right
- Left
- Anterior
- Posterior
- Transverse
Define fetal lie
The relation of the long axis of fetus to that of mother (longitudinal [99%] or transverse or oblique)
Describe the typical fetal attitude or posture
- Ovoid mass in shape of uterine cavity
- Back convex, head sharply flexed, thighs flexed over the abdomen, legs bent at knees, arches of feet rest on the anterior surface of the legs
- Cephalic presentation = arms crossed over thorax or parallel to sides
2 changes in the shape of the fetal head
- Caput succadaneum
- Molding
Define caput succedaneum
In prolonged labor before complete cervical dilatation, the portion of the fetal head over the cervical os become edematous (usually only a few mm thick)
Define molding in terms of changes in the shape of the fetal head
Changes from external compressive forces. Seldom overlapping of parietal bones (prevented by locking mechanism at the coronal and lambdoidal connections)
4 methods of diagnosis of fetal presentation and position
- Abdominal palpation
- Vaginal exmaination
- Auscultation
- Ultrasound
First Leopold maneuver
Palpate the fundus to determine the fetal pole present at the fundus
Second Leopold maneuver
Palms pressed on either side of the abdomen (back + extremities)
Third Leopold maneuver
Thumb and fingers of one hand, for presenting part
Fourth Leopold maneuver
Face the mother`s feet, adn with the tips of the fingers of both hands, exert deep pressure in the direction of the axis of the pelvic inlet
How to assess the degree of CPD through Leopold’s maneuvers
By evaluating the extent that the anterior portion of the fetal head overrides the symphysis pubis
Define the pelvic planes
Hypothetical flat surfaces on the pelvis located at the brim, cavity and pelvic outlet
Define the curve of Carus
Formed by an imaginary line that is drawn at the right angles of the pelvic planes
4 shapes of the pelvis
- Gynecoid
- Android
- Anthropoid
- Platypelloid
Define left occiput transverse (LOT) position
- Smaller posterior fontanelle (triangle shaped with three sutures radiating from it) on left of maternal pelvis
- Larger anterior fontanelle (diamond shaped with four sutures radiating from it) on opposite right side of maternal pelvis
Define occiput anterior
Head enters the pelvis with the occiput anteriorly and rotated away from the transverse position
Define occiput posterior
Where the fetus is facing up at delivery (often associated with a narrow forepelvis)
7 sequential positional changes during the second stage of labor
- Engagement
- Descent
- Flexion
- Internal rotation
- Extension
- External rotation
- Expulsion
Define engagement
The biperietal diameter of the fetal head, the greatest transverse diameter of the head in occiput presentations, passes through the pelvic inlet
Lowest point of the presenting part in engagement
At the level of the ischial spines
NOTE: +3 = perineum
4 forces that can bring about descent
- Direct pressure of the amniotic fluid
- Direct pressure of the fundus upon the breech with contractions
- Bearing down efforts with the abdominal muscles
- Extension and straightening of the fetal body
Importance of flexion in second stage of labor
Chin brought into close contact with fetal throad –> smaller diameter of fetal head (biparietal diameter) to be presented to the pelvis
When does internal rotation occur?
At the level of the ischial spines (0 station)
Define internal rotation in second stage of labor
Gradual turning of the occiput anteriorly, such that the agittal suture runs antero-posteriorly as the fetal vertex descends through the plane of the midpelvis
Define extension during the second stage of labor
Essential movement during birth process. When the sharply flexed fetal head meets the vulva, the occiput is brought in direct contact with the inferior margin of the symphysis
2 reasons why extension occurs
- Vulvar outlet is directed upward and forward, so must occur for head to pass through
- Expulsive forces of the uterine contractions and the woman’s pushing, along with resistance of the pelvic floor = anterior extension of the vertex in direction of the vulvar opening
Define external rotation (restitution)
Occiput returns to the oblique position from which it started and then to the transverse position (left or right). Corresponds to the rotation of the fetal body, bringing the shoulders into an antero-posterior diameter with the pelvic outlet
Compare the rhythm, intervals and intensity of contractions of true vs. false labor
True vs. False
- Rhythm = regular vs irregular
- Intervals = gradually shorten vs. unchanged
- Intensity = gradually increases vs. unchanged
Compare the location and sedation effect on discomfort in true vs. false labor
True vs. False
- Location = back and abdomen vs. lower abdomen
- Sedation = no effect vs. usually relieved
3 methods of confirming membrane rupture
- Pooling
- Nitrazine “dye” test
- Ferning
Describe the latent phase of labor
Uterine contractions can vary in intensity and frequency, but are sufficient to result in slow dilatoin and effacement of the cervix
Define the active phase of labor
Progressive cervical dilation
3 identifiable components of the active phase of labor
- Acceleration phase
- Linear phase of maximum slope
- Deceleration phase
5 elements accounted by the Bishop’s score
- Cervical dilation
- Cervical effacement
- Cervical consistency
- Cervical locations
- Station of fetal vertex
What does the Bishop’s score determine?
The favorability of the cervix and the risk of induction failure with an unripened cervis not be ripened
2 hormonal agents used for cervical ripening
- PGE1 (Misoprostol, aka cytotec)
- PGE2 (Dinoprostone, aka Prepidil gel, and cervidil insert)
Contraindication for hormonal cervical ripening
Prior C-section
Mechanical method of cervical ripening
Foley bulb inserted through the cervix into uterine cavity and then filled with approx 30 cc of normal saline. Gentle tension applied to catherter so that bulb sits at level of internal os
2 methods to augment labor
- Amniotomy
- Oxytocin administration
2 risks of amniotomy
- If done when head is not well applied to cervix, cord prolapse can result
- If done too early in the labor process, can increase risk of chorioamnionitis
When is C-section delivery indicated in the first stage of labor?
If progression of active labor does not occur with adequate contractions, an arrest of active phase is present
Define Erb’s palsy
Injury to the brachial plexus due to excessive traction with extension of the infant’s neck during delivery
Define episiotomy
Incision in the perineum that is either in the midline (median episiotomy) or begun in the midline, but directed laterally away from the rectum (mediolateral episiotomy)
4 signs of placental separation
- Uterus becomes globular and firm
- Sudden gush of blood
- Uterus rises in the abdomen. As the placenta, having been separated, passes down into the lower uterine segment and vagina, bulk pushes the uterus upward
- Umbilic cord protrudes farther out of the vagina, indicating that the placenta has descended
3 drugs to help uterus contract and decrease blood loss post-delivery
- Intravenous or intramuscular oxytocin
- Ergonovine
- PGF2a
Define first degree lacerations of the birth canal
Involvement of the fourchette, perineal skin and vaginal mucosa, but not the fascia and muscle
Define second degree lacerations of the birth canal
Involvement of skin, mucosa, fascia and muscles of the perineal body, but not the anal sphincter
Define third degree lacerations of the birth canal
Extension through the skin, mucosa, perineal body and involvement of the anal sphincter
Define fourth degree lacerations of the birth canal
Extensions of the third-degree tear through the rectal mucosa to expose the lumen of the rectum
