PTB

Question 1

What alternative steroid treatment can be offered to women at risk of preterm birth when betamethasone is not available?

Answer 1

Dexamethasone 6 mg IM q12h x4 doses

Question 2

What is the mechanism of action of antenatal steroids?

Answer 2

Accelerate development of type II pneumocytes leading to increased surfactant production

Question 3

How would you counsel a patient about the pros and cons of steroid administration between 34 and 36 weeks?

Answer 3

Pros: respiratory function improved, less TTN, surfactant use, CPAP, etc.
Cons: increased neonatal hypoglycemia, possible negative impact on long-term neurodevelopmental outcomes

Question 4

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?

Answer 4

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)

Question 5

List ten risk factors for spontaneous preterm birth.

Answer 5

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)

Question 6

How does digital cervical exam compare with ultrasound measurement of cervical length with regard to prediction of preterm birth?

Answer 6

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

Question 7

What degree of cervical shortening is expected in the second trimester of an uncomplicated pregnancy?

Answer 7

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)

Question 8

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?

Answer 8

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)

Question 9

What is the value of cerclage for women with a history of preterm birth?

Answer 9

Asymptomatic women with cervix < 25 mm before 24 weeks may benefit from cerclage - rate of PTB prior to 35 weeks is decreased

Question 10

List three reasons to stop administering magnesium sulfate for fetal neuroprotection.

Answer 10

Delivery has occurred
Delivery is no longer felt to be imminent
Patient has received 24 hours of therapy

Question 11

What is the mechanism of the neuroprotective effects of magnesium sulfate?

Answer 11

Improved cerebral vasodilatation
Decrease in circulating inflammatory cytokines and oxygen free radicals
Calcium influx into cells is inhibited

Question 12

What criteria define “imminent birth” and indicate the need for magnesium sulfate administration?

Answer 12

Active labour, 4+ cm dilated, with or without ROM

Planned PTB for fetal or maternal indications

Question 13

List three contraindications to magnesium sulfate use.

Answer 13

Hypersensitivity to the drug
Hepatic coma
Myasthenia gravis
Renal impairment (not an absolute contraindication, but use caution)

Question 14

List five maternal side effects of magnesium sulfate.

Answer 14

Flushing
Sweating
N&V
Hypotension (rare)
Tachycardia (rare)

Question 15

At what serum level can magnesium sulfate cause respiratory or cardiac arrest?

Answer 15

> 5 mM

Question 16

List four neonatal symptoms of hypermagnesemia.

Answer 16

Apnea
Hypoventilation
Weakness
Hypotonia
Absent/reduced deep tendon reflexes
Stupor
Coma

Question 17

Define cervical insufficiency.

Answer 17

Painless dilatation & shortening of the cervix prior to 37 weeks’ gestation in the absence of preterm labour.

Question 18

List five risk factors for cervical insufficiency.

Answer 18

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

Question 19

What is the rationale behind placement of a double cerclage?

Answer 19

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

Question 20

List two indications for emergency removal of a vaginal cerclage.

Answer 20

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

Question 21

What is the rationale for indomethacin use prior to cerclage placement?

Answer 21

Tocolytic effect
May decrease protruding membranes by decreasing fetal urine production
(Evidence is poor)

Question 22

What population benefits most from elective vaginal cerclage?

Answer 22

History of 3+ mid-trimester losses

Question 23

List three contraindications to the use of steroids for fetal lung maturation.

Answer 23

Active TB
Gastric ulcers
Chorioamnionitis

Question 24

List eight risk factors for PPROM.

Answer 24

Amniocentesis
Cervical insufficiency
Cerclage
Prior cone or LEEP
Previous PPROM
Previous PTL
Chronic placental abruption
Vaginal bleeding
Polyhydramnios
Multiples
Smoking
STIs
Low SES
BV

Question 25

List three things other than ruptured membranes which can cause ferning.

Answer 25

Antiseptic solution
Semen
Fingerprints
Cervical mucus

(Blood, meconium, vaginal secretions do not cause false positive ferning).

Question 26

What are the maternal benefits of IOL within 24 hours of PROM, compared with expectant management? What are the fetal/neonatal benefits?

(Term PROM trial, Cochrane review)

Answer 26

Maternal benefits:

• Reduced risk of chorioamnionitis (IOL w/ oxytocin or prostaglandin) without increasing CS or operative vaginal birth
• Improved maternal satisfaction (IOL w/ oxytocin specifically)

Fetal/neonatal benefits:

• Reduced need for monitoring in NICU
• Reduced neonatal infection (IOL w/ oxytocin vs prostaglandin/expectant management, benefit only seen for infants of GBS positive women)

Question 27

What are the pros & cons of preterm delivery versus expectant management for near-term (34-36+6) PPROM?

Answer 27

Preterm delivery reduces the risk of chorioamnionitis, has no significant effect on incidence of neonatal sepsis, is associated with mild respiratory and metabolic neonatal morbidity

Expectant management is associated with increased antepartum hemorrhage & intrapartum fever requiring antibiotics, but a lower cesarean section rate

Question 28

List five steps in management of early PPROM (between 24-32 weeks).

Answer 28

Avoid digital cervical exam
Assess for infection (cultures if indicated)
Consider collecting amniotic fluid from vagina to assess fetal lung maturity
US to assess fetal position, cervical status, fluid volume
Steroids for lung maturation
Antibiotics for GBS prophylaxis, if indicated
Antibiotics to increase latency period (typically erythromycin)
Consider transfer to tertiary care centre, if appropriate
Surveillance for chorioamnionitis (maternal vitals, FHR, uterine tenderness/irritability, WBC changes)
Antibiotics & IOL if chorioamnionitis develops