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

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

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

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.

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

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

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can result in cephalopelvic disproportion Bony pelvis can be measured by pelvimetry but it not accurate and thus has been replaced by a clinical trial of labor

Passage www.uptodate.com

Passage - Pelvimetry www.uptodate.com

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, 1-1.2 cm /hour, regular uterine contractions

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.

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.

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

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.

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 – 0.5-3 h; mulitG 0-30min

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

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

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

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

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.

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

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

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

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

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

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.

Cardinal Movements of Labor

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…