section name header

Info


A. Introduction navigator

  1. Parturition is act of giving birth to the young
  2. Labor is the physiologic process by which the fetus is expelled from the uterus
  3. Placenta derived maternal corticotropin releasing hormone (CRH) levels determine term
  4. Expulsion of fetus from uterus requires synchronized myometrial contractions
  5. Events associated with labor normally occur prior to spontaneous rupture of fetal membranes
  6. Preterm births occur in 5-15% of pregnancies
  7. Apgar scores at 1 and 5 minutes are the best prognostic factors for normal and preterm births [12]

B. Parturition [1] navigator

  1. Placenta produces CRH and secretes most of it into maternal circulation
  2. During pregnancy, CRH levels increase exponential through positive feed-forward loop
    1. CRH stimulates pituitary corticotropin (ACTH) production
    2. ACTH stimulates adrenal cortex to release cortisol (and stimulates DHEA-S production)
    3. Glucocorticoids further stimulate production of CRH by placenta
    4. Estrogen, progesterone and nitric oxide inhibit placental CRH production
    5. CRH availability is modulated by circulating CRH-binding protein (CRH-BP)
    6. Towards the end of pregnancy, CRH-BP levels fall, increasing available CRH
    7. Exponential increases in CRH signal end of pregnancy (parturition)
  3. In an individual woman, rate of change of CRH level is best predictor of onset of labor
  4. Dehydroepiandrosterone sulfate (DHEA-S) is converted to estrogen
  5. CRH levels also rise in the fetus
    1. CRH in the fetus stimulates fetal cortisol production
    2. This stimulates lung maturation, with production of surfactant A and phospholipids
    3. Surfactant A and phospholipids are inflammatory, stimulating myometrial contractions
  6. Combination of maternal and fetal events driven by CRH stimulate myometrial activity
  7. Myometrial Activity
    1. Uterus is normally in queiescent phase during pregnancy
    2. Quiescent phase composed of irregular, long-lasting contractions
    3. At onset of labor, regular, high-intensity, long-lasting contractions occur
  8. Umbilical Cord
    1. Clamping and cutting the umbilical cord is performed after the baby appears
    2. ~25-60% of (54-160mL) of combined fetal-placetnal circulation found in placenta
    3. Early clamping of umbilical cord associated with reduction in 20-40mL/kg of blood and ~30mg of iron versus delayed clamping
    4. Delayed clamping (2 minutes after birth) in full-term neonates associated with improved hematologic measures and iron status, reduced risk of anemia, in neonate [4]

C. Stages and Phases of Labornavigator

  1. Stage I
    1. Phase 0: Functional quiescence of myometrium
    2. Phase I: Latent, mild, irregular contractions - to "ripen" cervix
    3. Phase II: Active, accelerated dilation begins at 3-4 cm
    4. Phase III: Deceleration Phase to full dilation at10 cm
  2. Stage II - from full cervical dilation to delivery of baby
  3. Stage III - up to delivery of the placenta

D. Biochemistry of Labornavigator

  1. Phase 0
    1. Uterus maintained in state of functional quiescence
    2. Various inhibitors have been identified including:
    3. Progesterone
    4. Prostacyclin
    5. Relaxin
    6. Nitric oxide
    7. Parathyroid hormone related peptide (PTHRP)
    8. Various other molecules have a role
  2. Phase 1
    1. Uterus undergoes activation
    2. This is mainly due to effects of CRH on downstream events estrogen
    3. Drop in functional progesterone levels stimulates myometrial activation
    4. Prostaglandins E and F stimulate myometrial contractions
    5. Characterized by increased expression of contractile proteins and ion channels
    6. Increase in connexin 43, a gap junction protein, leads to coordinated myometrial function
  3. Phase 2
    1. Stimulation phase with increased uterine activity
    2. Prostaglandins E2 and F2alpha
    3. Oxytocin
  4. Phase 3
    1. Involution of uterus after delivery
    2. Oxytocin plays a major role
    3. Thrombin may also have a role
  5. Cervical Softening ("Ripening")
    1. Due to migration of inflammatory infiltrate into cervix
    2. Release of metalloproteases that degrade collagen
    3. Junction between decidua and and fetal membranesw breaks dosn
    4. Adhesive protein, fetal fibronectin, enters vaginal fluid
    5. Presence of fetal fibronectin in vaginal fluid predicts imminent delivery
  6. Inflammation due to infection can precipitate myometrial activation/contractions at any time during the pregnancy

E. Fetal Movement During Labornavigator

  1. Engagement
  2. Descent
  3. Flexion of neck
  4. Rotation (usually to Occipital-Anterior or OA)
  5. Extension
  6. External Rotation (Restitution then Shoulder Rotation)
  7. Expulsion (usually anterior shoulder first)

F. Determinants of Labor (the 3 "P's")navigator

  1. Power - Contractions
  2. Passenger - Size of Baby
  3. Passage - Size of pelvic opening

G. Abnormal Labornavigator

  1. Normal Labor takes ~12-14 hours for P0 (Para zero)
  2. Precipitous Labor
  3. Protracted Labor
    1. Prolonged Latent Phase - >20 hours for P0 or >14 hours in Pt/n
    2. Protracted Active Phase - <1.2 cm/hr for P0 or <1.5cm/hr in Pt
    3. Arrested Active Phase - no dilatation for >2 hours of fialure of descent for >1 hour
  4. Arrest or Failure of Descent
  5. Preterm Labor
    1. Labor prior to 37 weeks' gestation
    2. Occurs in ~8% of births
    3. Accounts for >85% of perinatal complications and death
    4. May reflect breakdown in mechanisms responsible for maintaining uterine quiescence
    5. May also be caused by overwhelming levels of uterine stimulating activities
    6. Does not appear to be caused by Trichomonas vaginalis infection [15]
  6. Pathophysiology of Preterm Labor / Birth [6]
    1. Four well described pathways, which may be initiated months before preterm labor
    2. Excessive myometrial and fetal membrane overdistention
    3. Decidual hemorrhage
    4. Precocious fetal endocrine activation
    5. Intrauterine infection or other inflammation
    6. Combinations of these processes may accelerate the process further
  7. Diagnosis of Preterm Labor / Parturition [6]
    1. Uterine contractions preterm are a poor predictor of actual labor
    2. Cervical dilatation, softening, shortening, can occur without imminent labor
    3. Preterm "labor" resolves spontaneously in ~30% of women
    4. Fetal fibronectin (vaginal fluid) and ultrasonography may accurately predict preterm labor
  8. Effects of Anesthesia on Labor
    1. Combination spinal/epidural anesthesia does not increase rate of cesarean deliveries
    2. Epidural anesthesia slighly increases length of labor but not rate of complications [8]
    3. Neonatal outcomes are better after epidural than parenteral opioids [8]
  9. Abnormal labor may contribute to intracranial injuries to the neonate [10]
  10. Prolonged labor (especially in developing countries) increases risk of vesicovaginal fistula [3]

H. Anesthesia and Analgesia [9] navigator

  1. ~60% of women chose analgesia for labor
  2. Epidural or spinal-epidural anesthesia usually selected
  3. Epidural Anesthesia
    1. achieved with catheter into lumbar epidural space usually between L3 and L4
    2. Local anesthetic AND/OR opioid are used
    3. Epidural analgesia initiated early in labor (cervix <4cm dilated) increases C-section risk [5]
    4. Early intrathecal analgesia followed by later epidural analgesia does not affect C-section rates and is better tolerated than systemic opiate analgesia [5]
  4. Combined Epidural-Spinal Anesthesia
    1. Has recently become popular
    2. Single dose opioid injected into subarachnoid space
    3. This allows rapid relief of pain with essentially no motor effects
    4. Epidural anesthesia also given
  5. Most studies show no effect of epidural anesthesia on C-section rates

I. Induction of Labornavigator

  1. Indications for Active Induction
    1. >42 weeks pregnancy (most common)
    2. Fetal Distress / Maternal Illness:
    3. Intrauterine growth retartdation
    4. Chronic placental insufficiency
    5. Preeclampsia
    6. Diabetes Mellitus
    7. Premature Rupture of Membranes (PROM)
    8. Infection (Chorioamnionitis)
    9. Rh Disease
    10. Active induction reduces postpartum hemorrhage and blood loss [6,14]
  2. Non-Pharmacologic Methods
    1. Dilateria (laminaria)
    2. Dilapan - synthetic cervical dilator
    3. Transcutaneous electrical nerve stimulator units (TENS)
    4. Walking has no effect on labor or delivery outcomes or types [7]
  3. Pharmacologic Methods
    1. Use of medical agents is considered "active" management of labor
    2. Oxytocin - 10IU intravenous (IV) or intramuscular; most commonly used
    3. Misoprostal - PGE2 analog 600µg orally
    4. Oxytocin slightly more effective and fewer side effects than misoprostal [14]
    5. Dinoprostone, PGE2 given intravaginally, induces labor
    6. Ergometrine or Syntometrine - may be used in combination with oxytocin
    7. Investigational: Mifepristone (RU 486)
    8. Pharmacologic induction is contraindicated in women with a history of Cesarean Section [13]
  4. Active versus Expectant Management of Labor
    1. Active intervention was oxytocic agent within 2 minutes of birth
    2. Active management also included immediate cutting and clamping of cord
    3. Delivery of placenta by controlled cord traction or maternal effort in active group
    4. Expectant management only included delivery of placenta by maternal effort
    5. Postpartum hemorrhage occurred in 16.5% of expectant and 6.8% of active groups
    6. Therefore, need to treat 10 women actively to prevent one postpartum hemorrhage
    7. Posture (supine or upright) had no effect on hemorrhage
  5. Routine episiotomy for vaginal delivery of no overall benefit, may be deleterious [17]

J. Indications for Cesarean (C-) Section navigator

  1. Infection: Herpes Simplex Virus, Group B streptococcus, HIV
  2. Arrested Labor (usually with failed induction attempt)
  3. Breech Presentation [11]
  4. Abnormal Maternal or Fetal Anatomy - cephalo-pelvic dysproportion
  5. Extremely large fetus
  6. Fetal Distress
  7. Placenta Previa
  8. Entangled Umbilical Cord
  9. Vasa Previa
  10. Previous C-Section [13,16]
    1. Increased risk of uterine rupture in women with previous C-section delivering vaginally
    2. Pharmacologic induction after previous C-section greatly increases rupture risk
    3. Absolute risk of death associated with trial of labor after C-section is low
    4. However, risk of death much higher with trial of labor versus planned C-section in women with previous C-section [16]

K. Postpartum Fever navigator

  1. Common obstetric complication
    1. Much more common in C-section patients than vaginal delivery
    2. Most C-section patients receive antibiotic prophylaxis
  2. Common Causes
    1. Endometritis (may progress to pelvic abscess)
    2. Urinary Tract Infection (UTI)
    3. Wound Infection (episiotomy usually)
    4. Phlebitis, Thrombosis
    5. Mastitis
  3. Endometritis
    1. Most common cause of postpartum fever
    2. ~2% of vaginal deliveries, 5-50% of C-sections
    3. Fever, uterine tenderness, foul smelling discharge
    4. Group B streptococcus (S. agalactiae) is common cause of fever <48 hours of delivery
    5. May progress or form pelvic abscess
  4. Mastitis
    1. Breast engorgement common postpartum
    2. Low grade fever may occur early after delivery (without infection)
    3. True mastitis occus 2-3 weeks postpartum
    4. Associated with cellulitis over breast area and fever to at least 39°C (102.2°F)
    5. Staphylococcus is most common infection; antibiotic therapy is indicated
    6. May be confused with inflammatory breast cancer
    7. Patients should be encouraged to continue breast feeding
  5. Empiric Therapy
    1. Fever >38°C in first 10 days postpartum
    2. Evaluate for common causes above
    3. Routine blood tests including complete blood count; urinalysis
    4. Empiric Antibiotics: Gentamicin + Clindamycin/Oxacillin or Ampicillin-Sulbactam
    5. Consider adding ampicillin or vancomycin to cover Enterococcus
    6. Ultrasound evaluation to rule out pelvic abscess, other pathology
    7. Consider mammography if inflammatory breast cancer suspected
    8. Persistant fevers despite antibiotic therapy - suspect septic pelvic thrombophlebitis
    9. Septic pelvic thrombophlebitis is treated with heparin

Resources navigator

calcApgar Score

References navigator

  1. Smith R. 2007. NEJM. 356(3):271 abstract
  2. Norwitz ER, Robinson JN, Challis JRG. 1999. NEJM. 341(9):660 abstract
  3. Wall LL. 2006. Lancet. 368(9542):1201 abstract
  4. Hutton EK and Hassan ES. 2007. JAMA. 297(11):1241 abstract
  5. Wong CA, Scavone BM, Peaceman AM, et al. 2005. NEJM. 352(7):655 abstract
  6. Simhan HN and Canritis SN. 2007. NEJM. 357(15):477
  7. Bloom SL, McIntire DD, Kelly MA, et al. 1998. NEJM. 339(2):76 abstract
  8. Halper SH, Leighton BL, Ohlsson A, et al. 1998. JAMA. 280(24):2105 abstract
  9. Elzschig HK, Lieberman ES, Camann WR. 2003. NEJM. 348(4):319 abstract
  10. Towner D, Castro MA, Eby-Wilkens E, Gilbert WM. 1999. NEJM. 341(23):1709 abstract
  11. Hannah ME, Hannah WJ, Hewson SA, et al. 2000. Lancet. 356(9239):1375 abstract
  12. Casey BM, McIntire DD, Leveno KJ. 2001. NEJM. 344(7):467 abstract
  13. Lydon-Rochelle M, Holt VL, Easterling TR, Martin DP. 2001. NEJM. 345(1):3 abstract
  14. Gulmezoglu AM, Villar J, Ngoc NTN, et al. 2001. Lancet. 358(9283):689 abstract
  15. Klebanoff MA, Carey JC, Hauth JC, et al. 2001. NEJM. 345(7):487 abstract
  16. Smith GCS, Pell JP, Cameron AD, Dobbie R. 2002. JAMA. 287(20):2684 abstract
  17. Hartmann K, Viswanathan M, Palmieri R, et al. 2005. JAMA. 293(17):2141 abstract