PTB Flashcards
What alternative steroid treatment can be offered to women at risk of preterm birth when betamethasone is not available?
Dexamethasone 6 mg IM q12h x4 doses
What is the mechanism of action of antenatal steroids?
Accelerate development of type II pneumocytes leading to increased surfactant production
How would you counsel a patient about the pros and cons of steroid administration between 34 and 36 weeks?
Pros: respiratory function improved, less TTN, surfactant use, CPAP, etc.
Cons: increased neonatal hypoglycemia, possible negative impact on long-term neurodevelopmental outcomes
What dose & route of progesterone would you recommend for a woman with a history of preterm labour? Would you recommend a different dose for a woman with a short cervix but no history of preterm labour?
Progesterone 100 mg pv daily for history of PTL (improved compliance, fewer side effects, fewer deliveries prior to 34 weeks compared with weekly IM 17OHP)
Progesterone 200 mg pv daily for short cervix (< 15 mm on TV US between 22-26 weeks)
List ten risk factors for spontaneous preterm birth.
Reproductive history: prior PTB, use of ART
Antepartum bleeding
ROM
Cervical/uterine factors: cervical insufficiency, fibroids, prior cervix excisional procedure
Fetal/intrauterine factors: multiple gestation, fetal anomaly, polyhydramnios
Infection: chorio, bacteriuria, periodontal disease, current BV & prior PTB
Demographics: low SES, single, low level of education, First Nations, > 35 years old
Lifestyle: smoking, drug use, stress, physical abuse
Inadequate prenatal care
Low pre-pregnancy weight
Poor pregnancy weight gain
(But many women who deliver preterm have no risk factors)
How does digital cervical exam compare with ultrasound measurement of cervical length with regard to prediction of preterm birth?
Digital exam underestimates cervix length (unless 2+ cm dilated, cannot assess length of cervix beyond vaginal fornices)
Therefore US is superior for prediction of PTB
What degree of cervical shortening is expected in the second trimester of an uncomplicated pregnancy?
No cervical shortening - length should be fairly consistent until the third trimester
(Slow change may be seen in women who go on to deliver preterm, or cervix may be stable until onset of PTL)
What is the value of TV US for cervix length in the low risk population? What about cerclage for short cervix in the same population?
No benefit to either
Cervix < 30 mm has PPV 4.5% for PTB prior to 35 weeks (since PTB is so rare in this population)
What is the value of cerclage for women with a history of preterm birth?
Asymptomatic women with cervix < 25 mm before 24 weeks may benefit from cerclage - rate of PTB prior to 35 weeks is decreased
List three reasons to stop administering magnesium sulfate for fetal neuroprotection.
Delivery has occurred
Delivery is no longer felt to be imminent
Patient has received 24 hours of therapy
What is the mechanism of the neuroprotective effects of magnesium sulfate?
Improved cerebral vasodilatation
Decrease in circulating inflammatory cytokines and oxygen free radicals
Calcium influx into cells is inhibited
What criteria define “imminent birth” and indicate the need for magnesium sulfate administration?
Active labour, 4+ cm dilated, with or without ROM
Planned PTB for fetal or maternal indications
List three contraindications to magnesium sulfate use.
Hypersensitivity to the drug
Hepatic coma
Myasthenia gravis
Renal impairment (not an absolute contraindication, but use caution)
List five maternal side effects of magnesium sulfate.
Flushing Sweating N&V Hypotension (rare) Tachycardia (rare)
At what serum level can magnesium sulfate cause respiratory or cardiac arrest?
> 5 mM
List four neonatal symptoms of hypermagnesemia.
Apnea Hypoventilation Weakness Hypotonia Absent/reduced deep tendon reflexes Stupor Coma
Define cervical insufficiency.
Painless dilatation & shortening of the cervix prior to 37 weeks’ gestation in the absence of preterm labour.
List five risk factors for cervical insufficiency.
Recurrent mid-trimester losses Previous PPROM prior to 32 weeks Cervix length < 25 mm prior to 27 weeks History of cervical trauma: repeat TAs, repeated cervical dilatation, cone biopsy, cervical lacerations, trachelectomy In utero exposure to DES Congenital uterine anomaly Connective tissue disease (eg. Ehlers-Danlos) PCOS
What is the rationale behind placement of a double cerclage?
Theory that two stitches = more support for cervix
Theory that placement of second suture at external os will facilitate retention of the mucous plug and therefore protect against ascending infection
List two indications for emergency removal of a vaginal cerclage.
Preterm labour unresponsive to tocolysis
Strong suspicion of chorioamnionitis/sepsis
PPROM (remove within 48 hours, typically after steroid administration) - delayed removal associated with increased neonatal mortality secondary to sepsis
What is the rationale for indomethacin use prior to cerclage placement?
Tocolytic effect
May decrease protruding membranes by decreasing fetal urine production
(Evidence is poor)
What population benefits most from elective vaginal cerclage?
History of 3+ mid-trimester losses
List three contraindications to the use of steroids for fetal lung maturation.
Active TB
Gastric ulcers
Chorioamnionitis
List eight risk factors for PPROM.
Amniocentesis Cervical insufficiency Cerclage Prior cone or LEEP Previous PPROM Previous PTL Chronic placental abruption Vaginal bleeding Polyhydramnios Multiples Smoking STIs Low SES BV
