Normal Labor and Delivery, Operative Delivery, and Malpresentations
John L. Wu
Betty Chou
Labor is defined as repetitive uterine contractions of sufficient frequency, intensity, and duration to cause progressive cervical effacement and dilation.
STAGES AND PHASES OF LABOR
The first stage of labor begins with the onset of labor and ends with full cervical dilation. It is divided into latent and active phases (Table 5-1).
The latent phase begins with regular contractions and ends when there is an increase in the rate of cervical dilation.
The active phase is characterized by an increased rate of cervical dilation and descent of the presenting fetal part, which may not occur until after 6 cm of dilation. It ends with complete cervical dilation and is further subdivided into:
Acceleration phase: A gradual increase in the rate of dilation initiates the active phase and marks a change to rapid dilation.
Phase of maximum slope: the period of active labor with the greatest rate of cervical dilation
Deceleration phase: the terminal portion of the active phase in which the rate of dilation may slow until full cervical dilation
The second stage of labor is the interval between full cervical dilation and delivery of the neonate.
The third stage of labor is the interval between delivery of the neonate and delivery of the placenta.
The fourth stage of labor, or puerperium, follows delivery and concludes with resolution of the physiologic changes of pregnancy, usually by 6 weeks postpartum.
TABLE 5-1 Stages and Phases of Labor | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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During this time, the reproductive tract returns to its nonpregnant state, and ovulation may resume.
MECHANISM OF LABOR
The cardinal movements of labor refer to the changes in position of the fetal head during its descent through the birth canal in vertex presentation:
Descent (lightening): movement of the fetal head through the pelvis toward the pelvic floor. The highest rate of descent occurs during the deceleration phase of the first stage and during the second stage of labor.
Engagement: the descent of the widest diameter of the presenting fetal part below the plane of the pelvic inlet. The widest diameter in cephalic presentation is the biparietal diameter. In breech presentation, the bitrochanteric diameter determines the station.
Flexion: a passive movement that permits the smallest diameter of the fetal head (suboccipitobregmatic diameter) to pass through the maternal pelvis
Internal rotation: The fetal occiput rotates from its original position (usually transverse) toward the symphysis pubis (occiput anterior) or, less commonly, toward the hollow of the sacrum (occiput posterior).
Extension: The fetal head is delivered by extension from the flexed position as it travels beneath the symphysis pubis.
External rotation: The fetal head turns to realign with the long axis of the spine, allowing the shoulders to align in the anterior—posterior axis.
Expulsion: The anterior shoulder descends to the level of the symphysis pubis. After the shoulder is delivered under the symphysis pubis, the remainder of the fetus is delivered.
MANAGEMENT OF NORMAL LABOR AND DELIVERY
Initial Assessment
History
Age, parity (full-term deliveries [≥37 weeks], preterm deliveries [≥20 to <37 weeks], abortions [<20 weeks], and living children), estimated gestational age
Labor-related symptoms including (a) onset, strength, and frequency of contractions; (b) leakage of fluid; (c) vaginal bleeding; and (d) fetal movement
Maternal drug allergies
Medications
Last oral intake
Review of prenatal labs and imaging studies including fetal ultrasounds
Past medical and surgical history, gynecologic history including abnormal Pap smears and sexually transmitted infections, obstetric history including birth weight and method of delivery of previous children, social history including tobacco/alcohol/illicit drug use
Physical Exam
Maternal vital signs (pulse, blood pressure [BP], respiratory rate, and temperature)
Confirmation of gestational age, where appropriate, and confirmation of viability at approximately 24 weeks
Assessment of fetal well-being (fetal heart rate)
Frequency and intensity of contractions
Fetal presentation
Estimated fetal weight (may be performed via Leopold maneuvers, as noted in the following procedures)
Step 1: Palpate the fundus to ascertain a fetal pole and obtain fundal height.
Step 2: Palpate the lateral walls of the uterus to determine fetal lie (vertical vs. transverse) and the location of fetal spine and extremities.
Step 3: Grasp and palpate the upper and lower poles to determine presentation, to assess mobility and fetal weight, and to estimate the amniotic fluid volume.
Step 4: Palpate the presenting part from lateral to medial to assess engagement in the maternal pelvis, the location of the fetal brow, and the degree of flexion.
Sterile speculum exam
Vulvar, vaginal, and cervical inspection (especially noting lesions or scars)
Evaluate for ruptured membranes (vaginal pooling of fluid in the posterior fornix, nitrazine test, and ferning seen on microscopic slide).
Wet mount, gonorrhea/chlamydia screening, group B Streptococcus (GBS) culture, if indicated
Sterile digital exam—defer if estimated gestational age is <34 weeks with ruptured membranes. This exam can provide the following data:
Cervical dilation is the estimated diameter of the internal os in centimeters. Ten centimeters corresponds to complete dilation.
Cervical effacement is the length of the cervix, expressed as the percentage change from full length, approximately 4 cm (0% or “long” means not shortened at all, whereas 100% means only a paper-thin rim of cervix is detected).
Fetal station describes the distance in centimeters between the presenting bony part and the plane of the ischial spines. Station 0 defines the level of the ischial spines. Below the spines is +1 cm to +5 at the perineum. Station above the spines is −1 cm to −5 at the level of the pelvic inlet.
Clinical pelvimetry: evaluation of the maternal pelvis by vaginal exam
Diagonal conjugate: The distance between the sacral promontory and the posterior edge of the pubic symphysis. A distance of at least 11.5 cm suggests a sufficiently adequate pelvic inlet for an average-weight fetus.
Transverse diameter: The distance between the ischial tuberosities, which can be approximated by placing a closed fist of known width at the perineum. An intertuberous diameter of at least 8.5 cm suggests an adequate pelvic outlet.
The pelvic type can be classified into four types based on general shape and bony characteristics. Gynecoid and anthropoid types are most amenable to a successful vaginal birth.
Standard Admission Procedures
Standard admission labs include urine testing (for protein and glucose), complete blood count (CBC), and a type and screen.
For patients without prenatal care, hepatitis B surface antigen, HIV, ABO blood group and antibody screen, urine culture and toxicology, rubella immunoglobulin G, CBC, and syphilis screening should be sent.
Intravenous (IV) access (heplock or continuous infusion) is recommended.
Informed consent for management of labor and delivery and for blood products should be obtained.
Management of Labor
The quality and frequency of uterine contractions should be assessed regularly by palpation, tocodynamometer, or intrauterine pressure catheter (if indicated).
The fetal heart rate should be assessed by intermittent auscultation, continuous electronic Doppler monitoring, or fetal scalp electrode (if indicated).
Cervical examinations should be kept to the minimum required to detect abnormalities in the progression of labor.
The lithotomy position is the most frequently assumed position for vaginal delivery in the United States, although alternative birthing positions, such as the lateral or Sims position or the partial sitting or squatting positions, are preferred by some patients, physicians, and midwives.
Induction of Labor
Indications: Induction of labor is indicated when the benefits of delivery (for the mother or fetus) outweigh the benefits of continued pregnancy. Induction should not be initiated if vaginal delivery is contraindicated (Table 5-2). Consideration of fetal lung maturity is necessary before elective induction of labor prior to 39 weeks of gestation. Amniocentesis is not necessary if the induction is medically indicated and the risk of continuing the pregnancy is greater than the risk of delivering before lung maturity. The favorability of the cervix at the time of induction is related to the success of labor induction. When the Bishop score (Table 5-3) exceeds 8, the
likelihood of vaginal delivery after induction is similar to that with spontaneous labor. Induction with a lower Bishop score has been associated with a higher rate of failure, prolonged labor, and cesarean delivery.
TABLE 5-2 Induction of Labor: Indications and Contraindications
Indications
Contraindications
Abruptio placentae, chorioamnionitis, gestational hypertension
Premature rupture of membranes, postterm pregnancy, preeclampsia, eclampsia
Maternal medical conditions (e.g., diabetes mellitus, renal disease, chronic pulmonary disease, chronic hypertension)
Fetal compromise (e.g., severe fetal growth restriction, isoimmunization)
Fetal demise
Elective inductions for gestational age >39 wk for logistical issues such as remote access to care, psychosocial reasons, and history of rapid deliveries. Typically only considered if cervix is favorable.
Vasa previa or complete placenta previa
Transverse fetal lie
Infection—active HSV, high viral load HIV
Pelvic structural deformities
Umbilical cord prolapse
Advanced cervical cancer
HSV, herpes simplex virus.
Adapted from American College of Obstetricians and Gynecologists—Obstetrics. ACOG practice bulletin no. 107: induction of labor. Obstet Gynecol 2009;114:386-397.
Cervical ripening may be used to soften the cervix before induction if the Bishop score is low. Cervical ripening can be achieved using pharmacologic and mechanical methods.
TABLE 5-3 Components of the Bishop Score
Rating
Factor
0
1
2
3
Dilation
Closed
1-2 cm
3-4 cm
5+ cm
Effacement
0%-30%
40%-50%
60%-70%
80%+
Station
-3
-2
-1, 0
> + 1
Consistency
Firm
Medium
Soft
—
Position
Posterior
Mid position
Anterior
—
Adapted from Bishop EH. Pelvic scoring for elective induction. Obstet Gynecol 1964;24:267.
Pharmacologic methods of induction of labor and cervical ripening
Low-dose oxytocin may be used with or without mechanical dilators.
Prostaglandin E2 is superior to placebo in promoting cervical effacement and dilation and may enhance sensitivity to oxytocin.
Prepidil gel contains 0.5 mg of dinoprostone in a 2.5-mL syringe; the gel is injected into the cervical canal every 6 hours for up to 3 doses in a 24-hour period.
Cervidil is a vaginal insert containing 10 mg of dinoprostone. It provides a lower rate of release (0.3 mg/hr) than the gel but has the advantage that it can be removed if uterine tachysystole occurs (>5 contractions in 10 minutes).
Prostaglandin E1 is also effective in stimulating cervical ripening.
Cytotec (misoprostol) is administered as 25 to 50 mg every 3 to 6 hours intravaginally. The use of misoprostol for cervical ripening is off-label.
Side effects: Any pharmacologic induction method includes a risk of uterine tachysystole. If oxytocin is being used, it can be titrated down or turned off with quick effect due to its short half-life. If Cervidil is being used, the insert can be removed. If indicated, a beta-adrenergic agonist (e.g., terbutaline sulfate) can be administered. Maternal systemic effects of prostaglandins may include fever, vomiting, and diarrhea.
Contraindications: A history of uterine scar or prior cesarean delivery, allergy to the medication, or active vaginal bleeding. Caution should be exercised when using prostaglandin E2 in patients with glaucoma or severe hepatic or renal impairment.
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