1. District 1 ACOG Medical Student Education Module 2008
Labor
District 1 ACOG Medical Student Education Module 2008

2. Labor
Labor is the physiologic process by which a fetus is expelled form the uterus to the outside world.
It involves the sequential integrated changes in the uterine decidua, and myometrium.
Changes in the uterine cervix tend to precede uterine contractions

3. Labor - Mechanics Uterine contractions have two major goals:
To dilate cervix
To push the fetus through the birth canal
Success will depend on the three P’s:
Powers
Passenger
Passage

4. Power Uterine contractions
Power refers to the force generated by the contraction of the uterine myometrium
Activity can be assessed by the simple observation by the mother, palpation of the fundus, or external tocodynamometry.
Contraction force can also be measured by direct measurement of intrauterine pressure using internal manometry or pressure transducers.

5. Power There is no specific criteria for adequate uterine activity
Generally 3-5 contractions in a 10 minute period is considered adequate labor

6. Passenger Passenger =fetus Fetal variables that can affect labor:
Fetal size
Fetal Lie – longitudinal, transverse or oblique
Fetal presentation – vertex, breech, shoulder, compound (vertex and hand), and funic (umbilical cord).
Attitude – degree of flexion or extension of the fetal head
Position
Station – degree of descent of the presenting part of the fetus, measured in centimeters from the ischial spines
Number of fetuses
Presence of fetal anomalies – hydrocephalus, sacrococcygeal teratoma

7. Passage Passage = Pelvis
Consists of the bony pelvis and soft tissues of the birth canal (cervix, pelvic floor musculature)
Small pelvic outlet can result in cephalopelvic disproportion
Bony pelvis can be measured by pelvimetry but it not accurate and thus has been replaced by a clinical trial of labor

8. Passage

9. Passage - Pelvimetry

10. The Stages of Labor First Stage
Interval between the onset of labor and full cervical dilation
Two phases:
Latent phase – onset o f labor with slow cervical dilation to ~4 cm and variable duration
Active phase – faster rate of cervical change, cm /hour, regular uterine contractions

11. The Labor Curve
First stage - A: latent phase; B + C + D: active phase; B: acceleration; C: maximum slope of dilation; D: deceleration; E: second stage. Adapted from: Friedman. Labor: Clinical evaluation and management, 2nd ed, Appleton, New York 1978.

12. Labor
Labor
NulliG
MultiG
1st Stage
Active
phase
Duration
6-18 h
2-10 h
Dilation
~1 cm/h
~1.5 cm/h
Arrested
>2 h
>2h
2nd Stage
0.5-3 h
5-30 min
3rd Stage
0-30 min
Freidman’s curve is a good guideline for expected progression in labor and therefore helpful to note abnormal labor patterns.

13. Labor Variables associated with longer labors:
Electronic fetal monitoring
Narcotic use
Maternal age >30
Ambulation

14. Labor – Second Stage
Interval between full cervical dilation to delivery of the infant.
Characterized by descent of the presenting part through the maternal pelvis and expulsion of the fetus.
Indications of second stage:
Increased maternal show
Pelvic/rectal pressure
Mother has active role of pushing to aid in fetal descent.

15. Labor – Second Stage
Examining the fetal head during the second stage may become difficult due to molding
Molding is the alteration of the fetal cranial bones to each other as a result of compressive forces of the maternal bony pelvis.
Caput is the localized edematous area on the fetal scalp caused by pressure on the scalp by the cervix.
PrimiG – h; mulitG 0-30min

16. Labor – Third Stage
The time from fetal delivery to delivery of the placenta
Three signs of placental separation:
Lengthening of umbilical cord
Gush of blood
Fundus becomes globular and more anteverted against abdominal hand

17. Labor – Third Stage
Placenta is delivered using one hand on umbilical cord with gentle downward traction. Other hand on abdomen supporting the uterine fundus.
Risk factor for aggressive traction is uterine inversion.
Obstetrical emergency!!
Normal duration between 0-30 min for both PrimiG and MultiG

18. Labor – Fourth Stage
Refers to the time from delivery of the placenta to 1 hour immediately postpartum
Blood pressure, uterine blood loss and pulse rate must be monitor closely ~ 15 minutes
High risk for postpartum hemorrhage from:
Uterine atony, retained placental fragments, unrepaired lacerations of vagina, cervix or perineum.
Occult bleeding may occur – vaginal hematoma
Be suspicious with increased heart rat, pelvic pain or decreased BP

19. Cardinal Movements of Labor
Refers to changes in the fetal head position during its passage through the canal.
Seven distinct movements:
Engagement
Descent
Flexion
Internal rotation
Extension
External rotation/restitution
Expulsion

20. Cardinal Movements of Labor
Engagement
Passage of the widest diameter fetal presenting part below the plane of the pelvic inlet
The head is said to be engaged if the leading edge is at the level of the ishial spines.

21. Cardinal Movements of Labor
Descent
Refers to the downward passage of the presenting part through the bony pelvis
Not steady process
Greatest at deceleration phase of first stage and during 2nd stage of labor

22. Cardinal Movements of Labor
Flexion
Occurs passively as the head descends due to the shape of the bony pelvis.
Partial flexion occurs naturally but complete flexion usually occurs only in the labor process
Complete flexion places the fetal head in optimal smallest diameter to fit through the pelvis

23. Cardinal Movements of Labor
Internal Rotation
Rotation of the fetal head from occiput transverse to occiput either in anterior or posterior position
Occurs passively due to the shape of the bony pelvis

24. Cardinal Movements of Labor
Extension
Occurs when the fetus has descended to the level of the vaginal introitus
When occiput is just past the level of the symphysis, the angle of the birth canal changes to upward position

25. Cardinal Movements of Labor
External Rotation/Restitution
As the head is delivered, it rotates back to its original position prior to internal rotation
It aligns anatomically with the fetal torso
The release of the passive forces on the fetal head allows it to return to appropriate position

26. Cardinal Movements of Labor
Expulsion
Delivery of the fetus
After delivery of the fetal head, descent and intraabdominal pressure by mother brings shoulder to the level of the symphysis
Downward traction allows release of the shoulder and the fetus is delivered.

27. Cardinal Movements of Labor

28. In Summary Know the different stages of labor Know the labor curve
Know the cardinal movements of labor
Know the causes of postpartum hemorrhage
The remaining talk regarding labor, induction, augmentation, surveillance and complications will be discussed in following lectures…