Preterm Labor

Aka: Preterm Labor

1. Definition of Preterm Labor
   1. Contractions with Uterine Cervical Length change
   2. Gestational age 20-37 weeks
      1. Late preterm: 34 to 37 weeks
      2. Early preterm: 32 to 34 weeks
      3. Very Early Preterm: >32 weeks
2. Epidemiology
   1. Incidence 7-8% of deliveries in 2014 (down from >10% in 2007)
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 <18 months
   4. Prior Cervical Cone Biopsy or LEEP (RR 2)
   5. Pyelonephritis
   6. Preterm cervical changes
      1. Advanced cervical dilatation
      2. Cervical Length decreased (<2.5 cm at <28 weeks is associated with a RR 6.19)
         1. Iams (1996) N Engl J Med 334(9): 567-72 [PubMed]
   7. Increased Uterine Size
      1. Multiple Gestation (50% of twin births, 90% of triplets are born before 37 weeks gestation)
      2. Polyhydramnios
   8. Low pre-pregnant weight (Body Mass Index <19.8 kg/m2)
   9. Low socioeconomic status or poor nourishment
   10. Prior preterm delivery (RR 1.5 to 2)
   11. History spontaneous second trimester abortion
   12. Black patients (14.9% preterm delivery vs 8.9% in non-hispanic white patients)
   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 [PubMed]
       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 [PubMed]
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: Five key concerns
   1. Precautions
      1. Preterm Labor patients who deliver within 6 days of presentation: <10%
         1. Assessment goal is to differentiate the patients at high risk of delivery
      2. Avoid digital vaginal exam UNLESS delivery is imminent (risk of infection)
         1. Perform sterile speculum exam and cervical Ultrasound instead
   2. Is patient preterm (<37 weeks)?
      1. Review Last Menstrual Period and prior Ultrasounds (especially earliest Ultrasounds)
      2. Late preterm: 34 to 37 weeks
      3. Early preterm: 32 to 34 weeks
      4. Very Early Preterm: >32 weeks
   3. Determine if patient is in labor
      1. Evaluate abdominal or Pelvic Pain
      2. Distinguish Preterm Labor from preterm contractions
      3. Findings most suggestive of Preterm Labor
         1. Contractions >6/hour
         2. Cervical dilatation >3 cm
         3. Cervical effacement >80%
         4. Preterm Rupture of Membranes
         5. Vaginal Bleeding
   4. Determine Uterine Cervical Length
      1. Avoid digital cervical exam due to infection risk (unless imminent delivery)
      2. Sterile speculum exam
      3. Ultrasound Exam of Uterine Cervical Length
   5. Determine if membranes are ruptured
      1. See Premature Rupture of Membranes
      2. See Labs below
   6. 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
   7. Evaluate maternal and fetal health
      1. Consider underlying injury or infection
         1. Recent Trauma (Placental Abruption may present with Vaginal Bleeding)
         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. AmniSure ROM Test (Placental alpha microglobulin 1 or PAMG-1 Protein Marker Test)
      2. Fluid seen pooling from cervical os
      3. Nitrazine Testing (pH 7.1 to 7.3)
      4. Ferning (arborization)
   2. Microscopy to evaluate Vaginitis
      1. Saline wet preparation (Trichomonas, Bacterial Vaginosis)
      2. KOH Preparation
   3. Culture
      1. Gonorrhea PCR
      2. Chlamydia PCR
      3. Group B Streptococcus Culture (Todd Hewitt media)
         1. Periurethral or outer-third of vaginal swab
         2. Rectal swab
      4. Urinalysis and 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 (3 cm or more) and negative fibronectin
       2. Suggests <10% chance of preterm delivery within 14 days
    3. References
       1. Iams (2002) N Engl J Med 346:250-5 [PubMed]
11. Evaluation
    1. Universal Cervical Length screening is not currently part of guidelines and is controversial
12. Management
    1. See Preterm Labor Management
13. Prevention
    1. Progesterone Therapy
       1. Indications
          1. Single gestation pregnancy (not useful in Multiple Gestation pregancies) AND
          2. Prior spontaneous preterm delivery OR Cervical Length <=2 cm before 24 weeks gestation
       2. Protocol: Prior spontaneous preterm delivery
          1. Hydroxyprogesterone caproate (Makena) 250 mg IM weekly from 16 to 24 weeks OR
       3. Protocol: Cervical Length <=2 cm before 25 weeks gestation
          1. Vaginal micronized Progesterone 200 mcg daily
       4. References
          1. Iams (2014) N Engl J Med 370(3): 254-61 [PubMed]
    2. Cervical Cerclage
       1. Indicated in Prior spontaneous preterm delivery AND Cervical Length <=2.5 cm before 24 weeks gestation
       2. Contraindicated in Multiple Gestation pregnancy (associated with increased preterm delivery risk)
       3. Owen (2009) Am J Obstet Gynecol 201(4): 375 [PubMed]
    3. Cervical Pessary (experimental)
       1. Associated with significantly decreased risk of preterm delivery
       2. Goya (2012) Lancet 379(9828): 1800-6 [PubMed]
14. References
    1. Iams in Gabbe (2002) Obstetrics p.755
    2. Rundell (2017) Am Fam Physician 95(6): 366-72 [PubMed]