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