Preterm Labor

Aka: Preterm Labor

1. Definition of Preterm Labor
   1. Gestational age 20-37 weeks
   2. Contractions with Uterine Cervical Length change
2. Epidemiology
   1. Incidence 7-8% of deliveries
3. Differential Diagnosis
   1. Gastrointestinal
      1. Appendicitis
      2. Constipation
   2. Uterus
      1. Uterine Fibroids
      2. Placental Abruption
   3. Urinary
      1. Acute Cystitis
      2. Pyelonephritis
      3. Nephrolithiasis
   4. Musculoskeletal
      1. Abdominal wall strain
4. Risk Factors
   1. No associated risk factor in 50% of Preterm Labor
   2. Tobacco abuse over 1/2 pack per day Cigarettes
   3. Interval between prior pregnancy <6 months
   4. Prior cervical cone biopsy
   5. Pyelonephritis
   6. Advanced cervical dilatation
   7. Increased Uterine Size
      1. Twin Gestation
      2. Polyhydramnios
   8. Low pre-pregnant weight (Body Mass Index <19.8)
   9. Low socioeconomic status or poor nourishment
   10. Prior preterm delivery
   11. History spontaneous second trimester abortion
   12. African American race
   13. Chemical Dependency (Cocaine, Heroin)
   14. Periodontal Disease
   15. Comorbidity
       1. Diabetes Mellitus
       2. Thyroid disease
       3. Hypertension
   16. Uterine anomaly
       1. Unicornuate Uterus or bicornuate Uterus
       2. Uterine Fibroids
       3. Diethylstilbestrol (DES) exposure in utero
   17. Genitourinary Infection (40% of preterm births)
       1. Urinary Tract Infection
          1. Pyelonephritis
          2. Asymptomatic Bacteriuria in Pregnancy
       2. Vaginal infections
          1. Group B Streptococcus (PPROM)
          2. Bacterial Vaginosis
             1. (1995) N Engl J Med 333:1732-42
       3. Sexually Transmitted Disease
          1. Neisseria gonorrhoeae
          2. Chlamydia trachomatis
          3. Trichomonas vaginalis
          4. Syphilis
       4. Infections with possible risk
          1. Ureaplasma urealyticum
          2. Mycoplasma hominis
   18. References
       1. Goldenberg (2008) Lancet 371(9606): 75-84
5. Symptoms
   1. Keep a high index of suspicion
      1. Contraction frequency does not predict risk
      2. Symptoms do not predict risk
   2. Pelvic pressure
   3. Vaginal pain
   4. Menstrual-like cramps
   5. Backache
   6. Vaginal Discharge or fluid leakage (see PPROM)
   7. Vaginal Bleeding
6. Signs
   1. Examine Cervix as soon as possible
      1. Assess Uterine Cervical Length and dilation
      2. Avoid cervical exam until labor if PPROM confirmed
   2. Examine Uterus
      1. Assess for Abruptio Placentae
      2. Check for firm, tender Uterus with minimal relaxation
7. Evaluation: Four key concerns
   1. Determine if patient is in labor
      1. Evaluate abdominal or Pelvic Pain
      2. Distinguish Preterm Labor from preterm contractions
   2. Determine Uterine Cervical Length
   3. Determine if membranes are ruptured
      1. See Labs below
   4. Establish clear gestational age
      1. Review Last Menstrual Period
      2. Review Estimated Due Date
      3. Review prior Ultrasound dating
      4. Does fundal height correlate with gestational age
   5. Evaluate maternal and fetal health
      1. Consider underlying injury or infection
         1. Recent trauma
         2. Vaginal infection
         3. Urinary Tract Infection in pregnancy
      2. Consider comorbidity
         1. Gestational Diabetes
         2. Pregnancy Induced Hypertension
         3. Intrauterine Growth restriction
         4. Oligohydramnios or Polyhydramnios
      3. Evaluate fetal activity and fetal health
         1. External Fetal Monitoring
8. Labs
   1. Evaluate for Rupture of Membranes
      1. Fluid seen pooling from cervical os
      2. Nitrazine Testing
      3. Ferning
   2. Microscopy to evaluate Vaginitis
      1. Saline wet preparation
      2. KOH Preparation
   3. Culture
      1. Gonorrhea Culture
      2. Chlamydia culture
      3. Group B Streptococcus Culture (Todd Hewitt media)
         1. Periurethral or outer-third of vaginal swab
         2. Rectal swab
      4. Urine Culture
      5. Consider non-genitourinary sources of infection
   4. Other Testing
      1. Fetal Fibronectin
         1. Reassuring if negative
         2. Poor Positive Predictive Value
      2. Urine testing
         1. Urinalysis and Urine Culture
         2. Urine Drug Screening
   5. Fetal Lung Maturity Assessment
      1. Indicated for 34 week gestation or greater
9. Imaging: Obstetric Ultrasound
   1. Fetal evaluation
      1. Biophysical Profile
      2. Amniotic fluid index
   2. Placental location
   3. Fetal Presentation
   4. Estimated Fetal Weight (EFW)
   5. Ultrasound Exam of Uterine Cervical Length
   6. Oligohydramnios (may suggest Rupture of Membranes)
10. Efficacy: Evaluation criteria
    1. Evaluation criteria do not predict preterm delivery
       1. Fetal Fibronectin
       2. Uterine contraction frequency
       3. Cervical Length assessment
    2. These criteria however have Negative Predictive Value
       1. No Cervical Length change and negative fibronectin
       2. Suggests <10% chance of preterm delivery
    3. References
       1. Iams (2002) N Engl J Med 346:250-5
11. Management
    1. See Preterm Labor Management
12. References
    1. Iams in Gabbe (2002) Obstetrics p.755