Preterm Labor

Question 1

Physiology/pathophysiology of preterm labor and preterm premature rupture of membranes (PPROM)

Answer 1

• Multifactoral, complex process, not well understood.
• Cervix undergoes considerable change, including collagen remodeling and altered cellular content→ effacement and dilatation
• 4 main pathways to cervical change

1. Premature activation of the maternal or fetal HPA axis → release of prostaglandins and stimulation of placental estrogens related to myometrium activation and labor.
2. Pathological uterine distention—Both multifetal gestation and polyhydramnios → increase the formation of gap junctions and oxytocin receptors → contractions.
3. Inflammation— systemic infection or ascending genital tract infections → inflammatory response → prostaglandin production → break down the extracellular matrix of the fetal membranes and cervix.
4. Decidual hemorrhage → release of thrombin → promotion of inflammation-associated PTB mechanisms.

Question 2

Define preterm birth

Answer 2

Birth sometime between 20 weeks - 37 weeks

*don’t round up

Question 3

High risk for preterm birth

Answer 3

Demographics

• <17 or >35 years
• Less education (<12 years)
• Single marital status
• Lower socioeconomic status
• Short interpregnancy interval (<18 months)

Prior obstetric/gynecological history

• Prior history of PTB
  
  • ​strongest risk factor
• Cervical surgery(cone biopsy, LEEP, etc.)
• Multiple cervical dilation and uterine evacuations
• Uterine anomalies

Nutritional status/physical activity

• Prepregnancy BMI <19 or weight <50kg
• Poor nutritional status
• Long working hours (>80h/week)
• Hard physical labor (including standing >8 hours)

Current pregnancy characteristics

• Assisted reproductive techniques
• Multiple gestation - one of the strongest risks
• Fetal disease
• Congenital malformations
• Poly- or oligohydramnios
• Maternal medical condition (e.g., hypertension, diabetes, thyroid disease, and asthma)
• Maternal abdominal surgery
• Psychological factors (e.g., stress, depression)
• Substance abuse, smoking
• Infection - BV, UTI, STDs
  
  • BV associated with 2x risk of PTB
• Short cervical length between 14 and 28 weeks Positive fetal bronectin between 22 and 34 weeks

Question 4

Fetal fibronectin testing (fFN)

Answer 4

• Glycoprotein found in high concentrations in amniotic fluid and the interface between the decidua and trophoblast cells
• Thought to play a role in implantation/maintenance of the attachment btw deciduas and fetal chorion
• Normally in the cervical and vaginal secretions before 16–20 weeks’ gestation, abnormal after 20 weeks, except as a marker of the imminent onset of labor at term.
• Positive test modestly useful in predicting the risk of a PTB occurring within 1–2 weeks
• Negative result more strongly predictive of no PTB (>90% negative predictive value)
• Dont do fFN if: bleeding, ROM, coitus, digital exam, or vaginal ultrasound within 24 hours
  
  • False neg – lube, soap, disinfectants inside vag

Question 5

Cervical length measurement

Answer 5

• Measured by transvaginal ultrasound
• Effective screening tool to predict PTB
  
  • Decreasing cervical length is associated with increased risk of PTB.
  • A short cervical length <25 mm in the early or late 2nd tri → marked increased risk of PTB
• False positives
• No utility in preventing PTB
• Increased predictive power of both tests when used in combo with fFN

Question 6

Symptoms of preterm labor

Answer 6

• Menstrual- like cramps or regular contractions
  
  • “Baby balling up”
• Low backache
  
  • near tailbone more concerning
• Diarrhea, urinary frequency - soft signs
• Sensation of pelvic pressure or thigh pain
• Sudden increase/change in vaginal discharge
• Intermittend lower abdominal pain

Question 7

Evaluation preterm labor and PPROM

Answer 7

• Decision to admit/discharge/transport should be made within 4 hours
• Evaluate uterus, assess size/contractions
• Thorough hx/OLDCARTS
• Sterile speculum exam → get swab for fFN in posterior fornix
  
  • Must get this first to be valid
  • pH – amniotic fluid is very alkaline
  • Look for ferning on dry slide
  • Look for pooling in posterior fornix – if you don’t see it, have pt valsalva/cough
• GC/CT cultures, GBS strep (outter 1/3 of vag and rectal area)
• Cervical exam - avoid if ROM (might be able to gauge from spec exam
• Abd u/s look for placental position, EFW, etc
• If ROM confirmed OR cervix > 3cm → hospitalize
• If intact membranes and cervix < 3 cm → send fFN

Question 8

Cervical exam findings and decision for tocolysis

Answer 8

(Kim’s lecture)

• >3 cm dilated, 80% effaced → PTL dx confirmed → tocolysis
• 2-3 cm dilated, < 80% → “iify” → observe, repeat exam in 1-2 hrs, look at cervical length, fFN
• < 2 cm or < 80 effaced → dx uncertain → watch for cervical change
• Cervical length < 20 mm concerning
• Cervical U/S → large role in evaluating PTL
• 20 – 30 mm: index of suspicion
• > 30 mm: PTL unlikely

Question 9

Preterm labor treatment

Answer 9

• Common tocolytics
  
  • Magnesium sulfate – loading dose: 4-6 grams then 1-4 grams/hr → blocks neuromuscular transmission → blocks contractions
    
    • Flushing, warmth, dry mouth , drowsy.
    • Check reflexes (first thing that diminishes with mag toxicity) and possible mag levels
    • Usually MD managed
    • Watch Urine output (risk of cardiac arrest)
  • Terbutiline (trade name: Brethine)
    
    • Not really used anymore due to maternal/fetal tachycardia and cardiac arrest
    • Doesn’t work well in terms of long term tocolysis
  • Procardia/nefedipine – Ca channel blocker
• Single course of steroids given before 32 weeks (2 doses) → reduces risk of RDS and IVH
• Bedrest – studies don’t show it to be effective
  
  • Not totally benign → deconditions muscles
• Recommend modified activity or pelvic rest (no orgasm)

Question 10

Modifiable Risk Factors

Answer 10

• Cigarette smoking – PTL, FGR
• Substance abuse – esp cocaine
• Infections – ie UTI, genital infection
• High levels of stress, inadequate social support – unsure of exact mechanism

Question 11

Methods of preterm labor prevention:

Weight and nutrition

Answer 11

• Underweight before pregnancy → doubles risk of PTB
• Calcium, iron, and omega-3 fatty acids important
  • Need 200-300mg omega 3s daily or eat fish 2-3x per week
  • Adequate iron stores
• Healthy, well balanced diet of 3 meals/day + 2 snacks

Question 12

Preterm birth prevention

Answer 12

• Mitigate modifiable risk factors:
  
  • Adquate weight and nutrition
  • Smoking cessation
    
    • one of the most important measures
  • Reducing infection
  • Avoiding cocaine
  • Avoiding a short (<18 months) interpregnancy interval
  • Dx and tx of asymptomatic bacteriuria
  • Improving sleep quality and reducing fatigue
    
    • Prolonged standing and working > 40 hours/week associated with PTB
• Progesterone
• Cerclage

Question 13

Preterm birth prevention:

Progesterone therapy

Answer 13

• May inhibit prostaglandins and ability of uterus to contract
• Hx of prior PTB: 250mg IM 17-hydroxyprogesterone caproate from weeks 16 through term in a singleton pregnancy
• Short cervix: Vaginal progesterone 100 mg if no prior spontaneous PTB and cervical length of 20mm or less at 24 weeks’ gestation or earlier.
• REFER/COMANAGE

Question 14

Who should be evaluated for cerclage?

Answer 14

• Prior history of cervical trauma such as conization or LEEP procedures
• Progressively earlier births
• 2 or more consecutive prior second-trimester pregnancy losses, or three or more early (<34 weeks) PTBs
• Offer if: prior PTD and cervix length < 15-24mm at < 24 weeks
• Consider transabdominal cerclage if suspected cervical insufficiency who have had unsuccessful cerclages before

Question 15

Diagnostic of preterm labor

Answer 15

• Documented regular UC ≥6/hour

AND

• At least one of the following:
  
  • Rupture of membranes
  • Cervical change
  • Cervix 2 cm dilated or 80% effaced

If criteria not met → false labor.

Question 16

Define: cervical insufficiency

Answer 16

• Classic definition: recurrent painless cervical dilation that leads to 3 or more midtrimester births
• More modern: both (1) TVU cervical length less than 25 mm and/or cervical changes detected on physical examination before 24 weeks of gestation and (2) prior sPTB at less than 37 weeks

Question 17

True or false: studies have found an association between the surgical treatment of CIN and spontaneous PTB

Answer 17

True

Question 18

What does PPROM stand for?

Answer 18

Preterm premature rupture of membranes

• clinical antecedent for up to 40% of PTB
• premature activation of the anatomic and biochemical changes the maternal decidua and adjacent fetal membranes usually undergo during the final weeks of gestation that ultimately result in a spontaneous rupture of the membranes

Question 19

True or false: Antibiotic therapy in preterm labor and intact membranes is effective in prolonging pregnancy or preventing preterm delivery

Answer 19

False

But treat to prevent GBS infection

(preterm infants more susceptible)

Question 20

Antenatal corticosteroids

Answer 20

• Promote surfactant synthesis, increase lung compliance, reduce vascular permeability, and generate an enhanced response to postnatal surfactant treatment. Also help brain, kidneys, and gut.
• Dosing:
  
  • 2 doses of 12 mg of betamethasone or combo of 6 mg each of betamethasones acetate and phosphate, IM x2, 24 hours apart
  • 4 doses of 6 mg of dexamethasone IM q 12 hours
  • May see transient rise in parental WBC (not > 20,000)
• Repeat if: antecedent tx given more than 2 wks prior, GA < 32⁶ weeks, and the clinician thinks delivery is likely within the coming week

Question 21

Magnesium sulfate

Answer 21

• May be neuroprotective for baby if given soon before delivery
• Appropriate for PPROM or PTL with high likelihood of imminent delivery (e.g., within 24 hours) or before an indicated preterm delivery.
• Do not delay emergency delivery for mag

Question 22

4 interventions shown to reduce perinatal morbidity and mortality

Answer 22

1. Transfer of the patient and fetus to an appropriate hospital before PTB
2. Administration of parental antibiotics to prevent neonatal GBS infection
3. Administration of parental corticosteroids to reduce neonatal RDS, IVH, and neonatal mortality
4. Administration of parental magnesium sulfate at the preterm delivery at < 32 weeks to reduce the incidence of CP

Question 23

Potentially preventable causes of PPROM

Answer 23

• Urogenital tract infections
• Poor parental nutrition with a low body mass index (<19.8 kg/m2)
• Cigarette smoking