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General obstetrics > Preterm Labour > Flashcards

Preterm Labour Flashcards

1
Q

What is the definition of moderate / late preterm labour?

A

32-36+6

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2
Q

What is the definition of very preterm labour?

A

28 - 31+6

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3
Q

What is the definition of extreme preterm labour?

Prevalence?

A

<28/40

0.5% births

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4
Q

What proportion of PTB is iatrogenic?

A

20-40%

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5
Q

What are four possible mechanisms for spontaneous PTL?

A
  1. Premature activation of maternal or fetal HPA axis
  2. Exaggerated inflammatory response or infection
  3. Decidual haemorrhage
  4. Pathological uterine distension
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6
Q

What are the risk factors for PTB (20!)

A

Previous PTB (15-30% recurrence, usually at same gestation)
Multiple gestation
IVF
Uterine anomaly including fibroids
Previous cervical surgery (particularly LLETZ >10mm or ≥2 LLETZ, cone biopsy)
Previous Evac/D&C - less association with medical Rx miscarriage/MTOP
PPROM
Previous 2nd trimester abortion
CS at fully
Polyhydramnios
Genital tract infection
Asymptomatic bacteruria
Systemic infection
Maternal chronic disease
APH - 1st trimester / praevia / abruption
Smoking
Extremes of age
Anaemia
IUGR
Fetal anomaly (or demise)
Social factors
Genetic factors

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7
Q

At what gestation (of prematurity) should you NOT do FBS and FSE?

A

< 34/40

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8
Q

What was the finding of the Cochrane 2013review looking at
- prenatal administration of progesterone to prevent PT in women considered to be at risk of PT

A

Progesterone reduced PTB and improved neonatal outcomes for:

  • women with a history of preterm birth or second trimester miscarriage
  • women with a shortened cervix <25mm
  • women who presented threatened pre-term labour

No significant evidence for its use in multiple pregnancies

Note OPTIMUM trial completed after this- RCT looking at the use of progesterone in these situations, found no benefit

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9
Q

`What was the finding of the Cochrane review looking at
- combinations of tocolytic drugs for inhibiting PTL?

A

Unclear whether combination therapy better than single tocolytic therapy

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10
Q

What was the finding of the Cochrane review looking at
- Calcium channel blockers for inhibiting PTL?

A

Benefits over placebo with regard to

  • number of women who birthed within 48 hours of starting treatment
  • serious neonatal morbidity and very/extrreme preterm birth rates
  • maternal adverse effects when compared to betamimetics
    but NO difference in perinatal mortality

Benefits over betamimetics, ORAs and MgSO4

https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD002255.pub2/full

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11
Q

What was the finding of the Cochrane 2019 review looking at
- antibiotics for asymptomatic bacteruria in pregnancy?

A

Overall poor quality data but may reduce:

  • risk of pyelonephritis
  • preterm birth rate
  • low birth weight
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12
Q

What was the finding of the Cochrane review looking at
- antibiotics for BV in pregnancy

A

Can eradicate BV, but overall risk of PTB was not reduced

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13
Q

What was the finding of the Cochrane review looking at
- effect of umbilical cord clamping in PTB

A

Delayed >30 seconds, rather than early, cord clamping may reduces the risk of death before discharge for babies born preterm.

Other outcomes were not significant.

Other studies have found DCC reduces need for blood transfusion, NEC and IVH in preterm babies.

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14
Q

At 23/40, what are the

  • survival rates
  • survival without major/minor morbidity
A

Survival rate - 60%

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15
Q

At 24/40, what are the

  • survival rates
  • survival without major/minor morbidity
A

Survival: 70-80%

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16
Q

At 25/40, what are the

  • survival rates
  • survival without major/minor morbidity
A

Survival rate: 80-85%

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17
Q

What is the mechanism by which steroids help lung development?

A
  1. Lung maturation - thinning of alveoli septum and differentiation of alvioli
  2. Induction of type 2 pneumocytes - increased surfactant production to reduce surface tension and pressure required to inflate lungs
  3. Increased NO production, causing vasodilation and improving pulmonary blood flow
  4. Increased epithelial Na channel expression - to promote movement of fluid from alveolar space to the interstitium
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18
Q

Until what gestation, should you consider rescue / repeat dose steroids?

How can repeats be prescribed?

A

Up till 32+6/40

  • Delivery expected within 7 days (even if likely within 24 hours)
  • Last dose >7 days ago
  • As single dose repeat, up to a maximum of 3 repeats
  • As a repeat course of 2 dose 24 hours apart, but NO further repeat doses after
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19
Q

What is the role of steroids prior to El LSCS

A

Can use past 34+6/40 “if there is known fetal lung maturity” and planned CS (RANZCOG/Liggins)

Aim CS ≥39/40

ASTECS 2005 Landmark Trial:

  • steroids significantly reduced SCBU/NICU admissions for respiratory distress RR=0.46
  • Reduction in RDS and TTN though not statistically significant
  • the benefits reduce with increasing gestation - recommendation to delay ELCS to >39wk if possible
  • ASTECS follow-up study (2013):
    • Following ACS administration no difference in school achievement of neurodevelopment outcome
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20
Q

What were the findings of the 2020 Cochrane Review looking at antenatal corticosteroids for accelerating fetal lung maturation in women at risk of PTB

A
  • Looked at steroids for suspected delivery prior to 37 weeks
  • Outcomes:
    • Perinatal mortality RR 0.85
    • RDS RR 0.71
    • Neonatal death RR 0.78

Likely reduction in:

  • IVH RR 0.58
  • Childhood developmental delay RR 0.5
  • Little to no effect on birthweight (-14g, wide CIs)
  • Maternal outcomes, chorioamnionitis, endometritis - no effect
  • Subgroup analyses key points
    • No difference in outcomes between the 2 overlapping subgroups 1) gestation <35+0, and 2) gestation 34-36+6
    • No difference in outcome when single course antenatal steroids vs weekly steroids as long as perceived risk of preterm birth

https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD004454.pub4/full

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21
Q

What were the findings of the Cochrane Review looking at antenatal corticosteroids for preventing respiratory compromise after CS at term?

A

May

  • reduce respiratory problems
  • reduce NICU admission

Further studies required

22
Q

What are the 4 proposed mechanism of action of Mg in fetal neuroprotection?

A
  • Downregulation of excitatory impulses - MgSO4 binds NMDA receptors preceding glutamate binding and initiation of calcium ion influx.
  • Vasodilation increasing cerebral blood flow
  • Reducing pro-inflammatory cytokines implicated in the process of preterm birth
  • Down regulating neurone cell apoptosis
23
Q

What effect does cervical cerclage have on PTB in
Women with an incidental finding of a short cervix?

A

Decreases RR 0.74

24
Q

What effect does cervical cerclage have on PTB in
Women with a short cervix and previous history of PTB

A

Decreases, RR 0.61

25
Q

What effect does cervical cerclage have on PTB in
Women with a short cervix and hx previous second trimester loss?

A

Decreases RR 0.57

26
Q

RANZCOG’s statement on cervical length measurement at mid-trimester scan

A

Assessment of cervical-length at 18-24/40 in women at LOW risk of PTB should be considered

TA scan length >35mm exclude shortening with sensitivity 95%

27
Q

What is the median cervical length at 20 weeks?

What is the cut off for a short cervix?

A

Median = 42mm

20 or 25mm, between 18-24/40

28
Q

Apart from cervical length, what three cervical features on USS are associated with PTB

A
  • Funnelling: effacement of the internal aspect of the cervix
  • Shortening in response to fundal pressure or uterine activity
  • Intra-amniotic sludge
29
Q

What is fetal fibronectin?

A

Fibronectin protein / glycoprotein produced by fetal cells, found at the interface of the chorion and the decidua

30
Q

At what depth of LLETZ is there an increased risk of PTB?

A

10mm

31
Q

At what gestation and situations should a rescue cerclage be considered?

A

16-27/40

Dilated cervix
Exposed, Unruptured fetal membranes

NICE guideline

32
Q

When should prophylactic cerclage be considered?

A

Cervical length <25mm between 16-24/40
AND either previous PPROM / hx cervical trauma

33
Q

When should prophylactic vaginal progesterone be considered?

A

Hx sPTB up to 34/40 OR mid-trimester loss

OR

TV USS between 16-24/40 with cervical length <25mm

Treatment should start between 16-24/40 and continue until 36/40

34
Q

What is the mortality rate of NEC?

A

40%

35
Q

What are fetal factors and clinical conditions that might increase the risk of adverse outcome in periviable preterm birth

A

Fetal factors

  • male sex
  • multiple pregnancy
  • congenital anomalies
  • fetal growth restriction

Clinical conditions

  • PPROM < 24/40
  • Chorioamnionitis
36
Q

Until what gestation should rescue dose steroids be considered?

A

32+6/40

Maximum 3 doses

RANZOCG

37
Q

How does magnesium sulphate work for neuroprotection?

(4 mechanisms)

A
  • Binds NMDA receptors and prevents influx of calcium ions and propagation of action potential, thus reducing excitatory impulses and hypoxic damage
  • Causes vasodilation promoting cerebral perfusion
  • Has anti-inflammatory properties
  • Anti-apoptotic activity
38
Q

What is the incidence of cerebral palsy?
What proportion occurs in preterm babies?
What are the leading risk factors for cerebral palsy?

A

2/1000 births
45% occurs in preterm infants

Risks:

  • Preterm delivery, especially < 34 weeks
  • extreme low birth weight <1500g

Obstetric contributors include chorioamnionitis, antepartum haemorrhage, complications of multiple pregnancy, placental insufficiency and, less commonly, perinatal asphyxia.
Neonatal intraventricular haemorrhage and periventricular leucomalacia are risk factors for CP and are inversely associated with gestational age.

39
Q

What is the incidence of preterm birth in NZ?

A

7.5% all births

40
Q

What is the evidence around steroids for late preterm delivery?

What is RANZCOG guidance?

A

Consider up till 34+6 if risk of preterm birth <35 weeks (RANZCOG/Liggins)

BUT evidence demonstrates possible benefit up to 37 weeks:

LANDMARK TRIAL - Antenatal betamethasone for women at risk for late preterm delivery (ALPS). Gyamfi-Bannerman et al. 2016

  • Multicentre randomised placebo-controlled trial
  • Inclusion: singelton pregnancy 34-36+6 pregnant with likely delivery by 36+6 weeks - Randomised to 2 doses betamethasone 24hr apart or placebo
  • Respiratory support in first 72 hours significantly reduced in betamethasone treatment group RR 0.80
  • Severe respiratory complications, TTN, bronchopulmonary dysplasia, resuscitation, surfactant use and duration of NICU stay also significantly reduced
  • No difference in chorioamnionitis, maternal or neonatal sepsis
  • significant increase in neonatal hypoglycaemia in betamethasone group RR1.60; but no serious adverse outcomes, but on average 2 day longer inpatient stay

Cochrane 2020

  • No difference between subgroups <35 wks and 34-36+6 in the positive effects of steroids for neonatal outcomes.
41
Q

What is the evidence for repeat doses rescue steroids?

A

LANDMARK TRIAL - Neonatal respiratory distress syndrome after repeat exposure to antenatal corticosteroids: a randomised controlled trial (ACTORDS). 2006

  • Multicentre randomised placebo controlled trial
  • Inclusion: Women <32 weeks with ongoing risk of preterm birth, and > 7 days after initial course steroid
    • Either given weekly steroid or placebo after initial steroid course, if ongoing risk PTB <32 wks
  • Findings:
  • Reduction in RDS RR = 0.82 and Severe RDS RR = 0.6
  • No effect on weight
  • significant reduction in oxygen requirement and duration of treatment

BUT Cochrane 2020 did not find significant difference for those given repeat course vs single course steroids…

42
Q

What are the potential adverse effects of steroids?

A
  1. Impaired fetal growth - Suggested in large retrospective study, but not borne out in recent cochrane review
  2. Hypoglycemia - ALPS study (large RCT) looking at ACS in later preterm showed increased risk hypoglycaemia
  3. Poorer school performance - LANDMARK - follow-up to ASTECS study looking at steroids prior to ElCS after 37 weeks showed no long term adverse effects for babies exposed to steroids
  4. Longterm health - Some evidence babies more likely to have higher BPs in adolescence and increased risk of T2DM in adulthood
43
Q

What is the evidence for magnesium sulphate for neuroprotection in PTB?

A

Cochrane 2009

  • Significant reduction in cerebral palsy RR 0.68
  • NNT 63
  • Also significant reduction in motor dysfunction
  • Included trials where magnesium given up to 34 weeks
  • Greater benefit seen at earlier gestations
  • No effect on perinatal mortality
44
Q

What is the evidence for progesterone use for preterm birth?

A

EPPPIC 2021 and Cochrane 2013

  • Reduces PTB for women with previous PTB and/or cervical length <25mm
  • Also reduced other adverse neonatal outcomes (BW<2.5 & 1.5kg, RDS, NICU admission, neonatal death)
  • Greatest effect seen for women with shortened cervix
  • No evidence of benefit for routine use in multiple pregnancy

LANDMARK TRIAL - Progesterone and the risk of preterm birth among women with a short cervix. (Fonseca et al. 2007)

  • Multicentre randomised placebo-controlled trial
  • >24,000 women
  • Inclusion criteria: cervical length <15mm at 20-25 weeks scan
  • Randomised to 200mg vaginal progesterone vs placebo from 24-34 weeks
  • 1st outcome: PTB < 34 weeks
  • Findings: delivery < 34 wks reduced in progesterone treatment group RR 0.56
45
Q

What is the evidence for cervical cerclage?

A

Cochrane 2017

  • Cerclage in history indicated cerclage and for shortened cervix reduced PTB <37, <34 and <28 weeks (RR 0.77), and reduced perinatal mortality.
  • No significant differences in outcome between the 5 at risk groups identified in studies: history‐indicated; short cervix based on one‐off ultrasound in high risk women; short cervix found by serial scans in high risk women; physical exam‐indicated; and short cervix found on scan in low risk or mixed populations
  • Insufficient evidence to compare outcomes for progesterone to cerclage, or to compare history indicated vs US indicated cerclage
46
Q

What is the RCOG guidance on cervical cerclage?

A

Cerclage indicated when:

  • 3 or more previous 2nd trimester miscarriages or PTB (history indicated cerclage)
  • History of previous 2nd trimester miscarriage or PTB AND cervical length <25mm on cervical surveillance (US indicated cerclage)
  • NB they do not recommend for incidental finding short cervix in absence of risk factors.
47
Q

What is the evidence for considering serial cervical surveillance in women with a history of PTB, versus history indicated cerclage?

A

Meta-analysis by Berghella and Mackeen (2011)

  • Compared pregnancy outcomes in singleton gestations with prior preterm birth that were managed either history-indicated cerclage, or cervical length (CL) screening with cerclage for short CL.
  • Four randomised controlled trials were included in the analysis. It found that CL screening with cerclage for short CL (ultrasound-indicated cerclage) was associated with similar incidences, compared with history-indicated cerclage
  • In the transvaginal ultrasound CL screening group, 42% developed a short CL and received cerclage.

Thus, ultrasound indicated-cerclage had similar results to history-indicated cerclage and nearly 58% of the women did not require cerclage when monitored for cervical length.

48
Q

How is cervical length measured?

A
  • Screening considered at 18-24 weeks
  • Can be TA, TV or transperineally
  • TV most accurate
  • Place transducer in anterior fornix
  • Don’t apply pressure on cervix
  • Take 3 measurements over 5 minutes and record the lowest measurement
  • Measure from internal to external os
49
Q

What is the evidence for prophylactic erythromycin in PPROM?

A

LANDMARK TRIAL: Broad-spectrum antibiotics for preterm, prelabour rupture of fetal membranes: the ORACLE I randomised trial. ORACLE Collaborative Group. 2001.

  • Multicentre randomised control trial
  • Inclusion: Confirmed PPROM, <37 weeks, Need for abs uncertain
  • Randomised to:- erythromycin 250mg, or augmentin 625mg, or both, or placebo, 4 times daily for 10 days
  • FINDINGS: Erythromycin significantly improved composite outcome (neonatal death, chronic lung disease, major cerebral abnormality on USS prior to discharge from hospital)
  • Erythromycin also:- prolonged duration of pregnancy, reduced oxygen requirement at 28 days, surfactant treatment and fewer major cerebral abnormalities, fewer positive blood cultures
  • augmentin alone, or augmentin with erythromycin had no benefit over placebo for 1st outcome
  • augmentin alone, or augmentin with erythromycin prolonged pregnancy, but was also associated with significantly increased rate of NEC
50
Q

Exclusion criteria for rescue cerclage:

A
  • PPROM
  • Infection
  • Bleeding
  • Uterine contractions
51
Q

When to perform a rescue cerclage?

A

Between 16-27+6

When cervix dilating and fetal membranes exposed but not in labour, no infection and no SROM

General obstetrics (34 decks)

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