eMedicine Specialties > Clinical Procedures > Obstetric and Gynecologic Procedures

Labor and Delivery, Normal Delivery of the Newborn

Author: Elizabeth Gittinger, MD, Instructor in Obstetrics and Gynecology, Boston University Medical School
Coauthor(s): Jodi F Abbott, MD, Associate Professor of Obstetrics and Gynecology, Clerkship Director, Boston University School of Medicine; Director, Antenatal Testing Unit, Boston Medical Center
Contributor Information and Disclosures

Updated: Feb 5, 2010

Introduction

The delivery of a full-term newborn refers to delivery at a gestational age of 37-42 weeks, as determined by the last menstrual period or via ultrasonographic dating and evaluation. The Naegel rule is a commonly used formula to predict the due date based on the date of the last menstrual period. This rule assumes a menstrual cycle of 28 days and mid-cycle ovulation. Ultrasonographic dating can be more accurate, especially when it is performed early in pregnancy and is used to corroborate or modify a due date based on the last menstrual period.

Approximately 11% of singleton pregnancies are delivered preterm and 10% of all deliveries are postterm. Thus, nearly 80% of newborns are delivered at full term, although only 3-5% of deliveries occur on the estimated due date.^1,2 Over the past few decades, the number of patients who go into spontaneous labor has decreased, and the percentage of inductions (iatrogenic labor) has increased to 22% of all pregnancies.²²

Labor and delivery is divided into 3 stages.

• In the first stage, the cervix dilates as a result of progressive rhythmic uterine contractions. This is typically the longest stage of labor. Cervical effacement, or thinning, occurs throughout the first stage of labor, and is graded 0-100%.
  • The first stage of labor is divided into the latent and active phases.
  • The latent phase can last for many hours. The cervix dilates, usually slowly, from closed to approximately 4-5 cm.
  • The active phase lasts from the end of the latent phase until delivery. It is characterized by rapid cervical dilation. The cervix usually dilates at a rate of 1.0 cm/h in nulliparous women and 1.2 cm/h in multiparous women during the active phase.
• The second stage of labor is the time between complete cervical dilation and delivery of the neonate. This phase lasts minutes to hours.
  • Six cardinal movements of labor occur during the second stage of labor.
    • Engagement of the head into the lower pelvis
    • Flexion of the head, putting the occiput in presenting position
    • Descent of the neonate through the pelvis
    • Internal rotation of the vertex to maneuver past the lateral ischial spines
    • Extension of the head to pass beneath the maternal symphysis
    • External rotation of the head after delivery to facilitate shoulder delivery
  • Several clinical parameters are followed.
    • The fetal presentation is determined by the first fetal body part that passes through the birth canal. Most commonly, this is the occiput or the vertex of the head.
    • The fetal station is the relation of the fetal head to the maternal ischial spines. The station is defined as -5 cm to +5 cm; 0 station is at the level of the ischial spines.
    • The fetal position is the orientation of the fetal vertex (the top of the head) in relation to the plane of the maternal ischial spines. The vertex normally rotates from a transverse position to an anterior or posterior position as the vertex internally rotates.
• The delivery of the placenta is the third and final stage of labor; it normally occurs within 30 minutes of delivery of the newborn. As the uterus contracts, a plane of separation develops at the placenta-endometrium interface. As the uterus further contracts, the placenta is expelled.

Indications

• Normal vaginal delivery of the newborn includes the following circumstances:
  • Spontaneous labor mediated by pituitary and placental hormone cascades
  • Rupture of amniotic and chorionic membranes (suggested by the presence of a watery vaginal discharge or new oligohydramnios on ultrasonograph)
  • Induction of labor (indicated if fetal or maternal medical conditions necessitate delivery)
• While sporadic contractions may occur, and the cervix may begin to soften in anticipation of delivery, the presence of contractions that lead to active cervical change defines labor.
• Not all vaginal fluid is amniotic fluid, and membrane rupture requires confirmation.
• If the cervix is favorable, oxytocin is given to induce uterine contractions. A favorable cervix is defined by the Bishop score, which includes parameters like cervical dilation, softening, effacement, and station. If the cervix is not favorable and no contraindications are present, cervical ripening can be facilitated with intravaginal prostaglandins before oxytocin is initiated.³
• A balloon catheter can also be used for ripening. Pennell et al compared 3 methods of ripening the cervix in nulliparous women at term and found that the single-balloon catheter offers the best combination of safety and patient comfort. In a randomized controlled trial, 330 nulliparous women with unfavorable cervices induced at term were treated with 1 of 3 methods: double-balloon catheters, single-balloon catheters, or prostaglandin gel. Cesarean delivery rates were high with all 3 methods. Single-balloon catheter use was associated with earlier delivery and with significantly less pain: 36% of patients had a pain score of ≥4, vs 55% of patients treated with double-balloon catheterization and 63% of those treated with prostaglandin gel (P <0.001). Induction was complicated by uterine stimulation in 14% of patients in the prostaglandin arm, but none of those in the catheter arms, and mean cord arterial pH was lower in the prostaglandin arm (7.25 vs 7.26 in the catheter arms [P =0.050]).²⁴
• For more information, see eMedicine's Cervical Ripening article.

Contraindications

• While most full-term newborns in the United States are delivered vaginally, vaginal birth is contraindicated in some circumstances, including those described in this section.
• Cord prolapse
  • When cord prolapse is detected on pelvic examination, the clinician should leave the hand in place, applying pressure against the presenting fetal part to keep it as far out of the pelvis as possible to prevent cord compression.
  • The incidence of cord prolapse is directly proportional to cord length.
  • The treatment is immediate conversion to cesarean delivery. If not treated emergently, cord prolapse is associated with high perinatal mortality.
• Brow presentation
  • This may convert to face or vertex presentation and may be managed expectantly.
  • If the patient is unstable or no conversion occurs, cesarean delivery is recommended.
• Face presentation
  • Clinicians and mothers may tolerate a trial of expectant management, if cephalopelvic disproportion is not suspected and if the face is in a mentum anterior or mentum transverse position.
  • If the face is mentum posterior (chin facing the maternal sacrum), a cesarean delivery is required.
• Breech presentation
  • Up to 5% of all fetuses and 1-3% of full-term pregnancies present in the breech position. Plan for abdominal delivery for a footling presentation. For frank breech (ie, hips flexed, knees extended) and complete breech (ie, hips and knees flexed) presentations detected before the onset of labor, manual pressure maneuvers called external cephalic version (ECV) may be performed to attempt conversion to a vertex presentation.
  • The success rates of ECV are greater than 50% in properly selected patients, but these maneuvers should be performed at term, as they may stimulate labor or result in complications that necessitate prompt delivery.
  • The American Congress of Obstetricians and Gynecologists (ACOG) recommends abdominal delivery if ECV fails or if a mother in labor presents with breech presentation, as the rates of fetal morbidity and mortality in these cases are increased with vaginal delivery.⁴
• Malposition
  • Fetal positions compatible with vaginal delivery are occiput anterior (OA), right occiput anterior (ROA), and left occiput anterior (LOA).
  • The occiput posterior (OP) position can be unfavorable for passage through the birth canal. Labor progress should be monitored for progression. If the fetal station is high and without descent during labor, change to abdominal delivery should be considered.
  • Deep transverse arrest occurs when the fetal head remains in transverse position without descent. Unfavorable maternal pelvic anatomy is the most common cause; abdominal delivery should be considered promptly.
  • Shoulder presentation is a sign of a transverse fetal lie. If this presentation is detected prior to active labor, external rotation through ECV may be attempted. When this presentation is detected during labor, maternal risk for infection, uterine rupture, or both is high. Emergent abdominal delivery is indicated.
• Twin pregnancy
  • If a nonvertex second twin presentation occurs, it is managed according to gestational age, maternal preference, and practitioner comfort. The exceptions to vaginal delivery include the following:
    • Presenting twin in breech position
    • Conjoined twin anatomy
    • Most cases of mono-amniotic twins
    • Signs of fetal distress or an abnormality that warrants abdominal delivery
• Higher order births
  • In the United States, cesarean delivery is planned for higher order births.
• Vaginal delivery after cesarean delivery
  • While safe in most circumstances, vaginal delivery after previous cesarean delivery remains controversial because of the rare but serious complication of uterine rupture. The risk of uterine rupture is approximately 0.5% in patients who have had one prior low transverse cesarean delivery.
  • The success rate of this procedure is greater than 50%.
  • During the delivery, careful fetal and maternal monitoring are needed to detect early signs of dystocia or uterine rupture.
  • An in-house anesthesiologist and obstetrician should be available in case complications arise. This type of delivery is not offered in many small hospitals because of the inconsistent availability of anesthesia or operating room staff.
  • This type of delivery is contraindicated in cases of multiple prior cesarean deliveries, a history of a classical or T-shaped uterine scar, the presence of placenta previa, the presence of other uterine scars, or concern for true cephalopelvic disproportion.
• Nonreassuring fetal heart rate patterns
  • Hospital protocols in the United States recommend some form of intermittent fetal heart rate monitoring. The need for continuous fetal heart rate monitoring remains unproven in low-risk, full-term pregnancies; however, changes in fetal heart rate monitoring can signal fetal distress and may indicate the need for emergent abdominal delivery.
  • Causes of fetal distress include placental abruption, placental insufficiency, or a tight nuchal cord. Most cesarean deliveries undertaken for suspected fetal distress result in healthy birth outcomes.
• Macrosomia
  • Fetal weight greater than 4000-4500 g is associated with a higher risk of shoulder dystocia and birth trauma during vaginal delivery.⁵
  • Mothers with diabetes have a higher incidence of macrosomia and risk of shoulder dystocia.
  • If the estimated fetal weight is greater than 4500 g in a mother with diabetes, ACOG recommends abdominal delivery.
  • If the mother does not have diabetes, abdominal delivery is not recommended until an estimated fetal weight of 5000 g.
• Abnormal placentation
  • Placenta previa (the placenta implanted over the cervical os) is a contraindication to vaginal delivery because of the risk of hemorrhage as the cervix dilates.
  • Placenta previa complicates up to 2% of all pregnancies. Risk factors include artificial reproductive technology and prior cesarean delivery.

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