6.4 Preterm labour

Question 1

What is definition of preterm labours?

Answer 1

all deliveries between 24+0 to 36+6 weeks with a foetus weighing >500g → subclassified based on gestational age

Question 2

what gestational is considered mildly preterm ?

Answer 2

32+0 to 36+6 weeks

Question 3

what gestational is considered moderately preterm ?

Answer 3

28+0 to 31+6 weeks

Question 4

what gestational is considered extremely preterm ?

Answer 4

24+0 to 27+6 weeks

Question 5

when is term delivery?

Answer 5

labour occurring ≥37+0 weeks and <42+0 weeks of gestation

Question 6

when is foetal viability?

Answer 6

from 24 weeks of gestation onwards (occasionally survive at 23 weeks)
o Survival increases with gestational age (8% at 23 weeks, 78% at 26 weeks)

Question 7

When is resuscitation not offered?

Answer 7

Below 23+0 weeks

Question 8

when is resuscitation based on parent’s wishes?

Answer 8

23+0 to 23+6 weeks

Question 9

when is resuscitation offered to all neonates?

Answer 9

From 24+0 weeks

Question 10

what is still birth?

Answer 10

Foetal death after 24 weeks gestation

Question 11

what is perinatal mortality?

Answer 11

Still births + neonatal deaths through 28 days of life (per 1000 total births → does not need to be live births)

Question 12

what is infant mortality?

Answer 12

Deaths among live born infants before 1 year of age (per 1000 live births)

Question 13

what is perinatal morbidity?

Answer 13

Specific diseases or conditions related to immaturity of various organ systems

Question 14

what are factors affecting outcome of preterm birth?

Answer 14

The above outcomes are influenced by the following factors:
• Gestational age (better if older)
• Birth weight (<500g is associated with extreme prematurity, significant morbidity & mortality)
• Foetal weight (singleton vs multiple gestation)
• Geographic location (proximity to neonatal care unit, efficiency of care)
• Maternal/foetal conditions that led to the preterm birth

Question 15

what are the immeidate complications of preterm labour?

Answer 15

• Respiratory distress syndrome (RDS) (most common complication)
• Intra-ventricular haemorrhage (IVH)
• Bronchopulmonary dysplasia (BPD)
• Patent ductus arteriosus (PDA)
• Necrotising enterocolitis (NEC)
• Retinopathy of prematurity (ROP)

Question 16

What are the long term complications of preterm labour?

Answer 16

Prematurity is associated with several major lifetime consequences including:
• Chronic lung disease
• Grade 3 or 4 IVH associated with cerebral palsy
• Visual & hearing impairment
• Neurosensory impairment, reduced motor & cognitive performance, academic difficulties

Question 17

What are spontaneous causes for preterm delivery?

Answer 17

• Idiopathic PTD (40%) → spontaneous onset
• Preterm premature rupture of membranes (PPROM) (40%) → rupture of amnion & chorion membranes before onset of labour at <37 weeks gestation

Question 18

what are acquired causes for preterm delivery?

Answer 18

• Iatrogenic causes (20%) → delivery undertaken for maternal or foetal indications (benefits of delivery > continuation of pregnancy

Question 19

The exact pathophysiology of PTL is unknown but the causes are multifactorial:
• Common pathway: activation of _____________ & release of _____________ → myometrial contraction, cervical dilatation, membrane rupture
• Risk factors: stress, infection, haemorrhage, uterine distension, cervical incompetency, undernutrition

Answer 19

matrix metalloproteinases (MMPs);

prostaglandins

Question 20

How does stress cause Preterm labour?

Answer 20

Psychological & physical stress causes release of catecholamines, cortisol, oxytocin → activation of HPA axis (CRH release) → increased prostaglandins → increased myometrial contractility

Question 21

How does infection cause Preterm labour?

Answer 21

Inflammation causes cytokine, prostaglandin, MMP release → triggers uterine contractions, cervical dilatation, degradation of cervical plug → further colonisation of decidual space by more bacteria:
• Results in PTL ± chorioamnionitis

Question 22

How does haemorrhage cause Preterm labour?

Answer 22

Intrauterine haemorrhage causes release of thrombin → increased prostaglandins → myometrial contraction • Blood acts as a uterine irritant → triggers activity

Question 23

How does uterine distension cause Preterm labour?

Answer 23

Myometrial stretch causes expression of gap junctions → increased prostaglandins → uterine activity

Question 24

How does cervical incompetence cause Preterm labour?

Answer 24

Weakness of the cervix causes painless cervical dilatation before the onset of labour (rare cause in 2nd & 3rd trimesters):
• Most actually have a structurally normal cervix
• May occur after previous surgery to cervix (e.g. loop excision, cone treatment for cervical dyskaryosis, repeated surgical dilatation of cervix, cervical trauma, anatomical anomalies

Question 25

How does iatrogenic cause Preterm labour?

Answer 25

Induced for certain conditions (e.g. placental insufficiency, severe pre-eclampsia, signs of foetal distress

Question 26

what is intrauterine infections more likely to cause?

Answer 26

Intrauterine infections (e.g. bacterial vaginosis, GBS, gonorrhoea, chlamydia) are more likely to be contributory in earlier gestation

Question 27

what is extrauterine infections more likely to cause?

Answer 27

Extrauterine infections (e.g. UTIs, asymptomatic bacteriuria, systemic maternal infections like appendicitis, periodontal) cause cytokine release or haematogenous bacterial spread to uterus

Question 28

The trans-vaginal US (TVUS) measures ____________ & identifies any ______________: • Optimal time:_______________ • Normal cervical length: ~35mm o Cervical length <15mm is associated with 50% risk of delivery <32 weeks o High negative predictive value → reassurance if _________________ • Indications for serial measurement: _________________ • Benefits: helpful in diagnosing PPROM → look for oligohydramnios in absence of foetal urinary tract abnormalities or intrauterine growth restriction (IUGR)

Answer 28

cervical length; funnelling (dilatation of the internal os of the cervix & cervical shortening); 16 – 24 weeks gestation; length >3cm at 24 weeks; previous PTL, previous 2nd trimester loss

Question 29

Foetal fibronectin is a glycol-protein that acts as a glue between the foetal & maternal membranes and is found in vaginal secretions in early pregnancy: • Typically absent from cervicovaginal secretions between 24 – 34 weeks gestation (due to ___________________) o Presence indicates __________________ before the onset of labour → high risk for PTL • Sampling method: swab from ___________________ → send for immunoassay • Advantages: o Higher positive predictive value for PTL in the following 7 – 10 days compared to digital examination → positive result indicates 50% risk of PTL o High negative predictive value (up to 99%) • False positives may result from the presence of alternative proteins (e.g. __________________)

Answer 29

fusion of chorion & decidual membranes; disruption between membranes & decidua; posterior fornix; lubricating jelly, recent sexual intercourse, vaginal bleeding, PPROM

Question 30

how is preterm labour diagnosed?

Answer 30

Preterm labour is diagnosed based on the following criteria: 1. Gestational age <37+0 weeks 2 2. Presence of regular uterine contractions (palpable or recorded on CTG) occurring every 5 – 10 min 3. Evidence of cervical changes (effacement of 80% and dilatation of ≥2cm) Note that preterm labour is not equivalent to preterm birth (only 8 – 24% presenting with symptoms of PTL will actually deliver prematurely)

Question 31

what are differentials for pre term labour?

Answer 31

UTI, uterine irritability, placental abruption, urinary incontinence

Question 32

what is needed for the history of preterm labour?

Answer 32

* Establish accurate gestational age * Symptoms: abdominal pain (constant or intermittent), cramps, back pain, vaginal bleeding, spotting, show, leaking of liquor (amniotic fluid) * Complications: dysuria (UTI), diarrhoea (GI infections) * May also be asymptomatic or vague symptoms with cervical incompetence (vaginal discharge, cervical dilatation)

Question 33

what is needed for the examination of preterm labour?

Answer 33

* General: pyrexia, tachycardia, hypotension → sepsis * Abdominal: contractions, tenderness * Speculum: cervical effacement, dilatation, membranes, blood, pooling of liquor (collection of amniotic fluid that can be seen in the vaginal fornix), offensive discharge (ruptured membranes/intrauterine infection) * *Avoid repeated vaginal examinations in PPROM!

Question 34

what is needed for the investigation of perterm labour?

Answer 34

The following investigations are used in patients with suspected PTL: • FBC & inflammatory markers (CRP) → possible infection • Urinalysis (dipstick & UFEME) & urine cultures → UTIs • High vaginal swab → vaginal infections, GBS • Actin partus/foetal fibronectin (FFN): rapid tests from week 20 until birth • Obstetric US: assess presentation, liquor volume, placental position, estimated foetal weight, cervical length

Question 35

why is cardiotocography used to evaluate preterm labour

Answer 35

• Monitor foetal heart rate & uterine contractions

Question 36

How do tocolytics help with preterm labour?

Answer 36

Tocolytics are anti-contraction drugs used to suppress preterm labour, but tocolytics alone have not been shown to reduce rates of PTD or improve neonatal outcome: • Effect: prolongation of pregnancy for up to 48h → allow time for administration of antenatal steroids, in-utero transfer, maternal MgSO4

Question 37

what are examples of tocolytics?

Answer 37

nifedipine (Adalat), indomethacin, atosiban, salbutamol

Question 38

when is the optimum time to give tocolytics?

Answer 38

before 34 weeks (not recommended thereafter)

Question 39

what are the contraindications to tocolytics?

Answer 39

severe pregnancy-induced hypertension, antepartum haemorrhage with abruption, non-reassuring foetal status, overwhelming sepsis

Question 40

when is antibiotics needed for preterm labour?

Answer 40

The routine prescription of antibiotics is not recommended if membranes are intact: • Only initiated in labour to prevent neonatal GBS infection (in the event of PPROM or suspected chorioamnionitis

Question 41

what is the effect of corticosteroids?

Answer 41

Corticosteroids are administered to all women at risk of PTL between 24+0 to 34+6 weeks: • Effects: reduction of neonatal death, RDS, NEC, cerebrovascular haemorrhage, and NICU admissions • Mechanism of action: (1) stimulates pneumocytes to produce surfactant (2) aids the structural development of lung (3) intestinal maturation

Question 42

when is the optimum timing for coticoid steroids to be prescribed?

Answer 42

from 24h to 7 days before delivery

Question 43

why is magnesium sulfate prescribed for preterm labour?

Answer 43

Magnesium sulfate is a neuroprotective agent in preterm infants (dosing is unclear): • Maternal administration may reduce risk of cerebral palsy in the preterm neonate (normally 14.6% at <28 weeks gestation & 6.2% between 28 – 31 weeks)

Question 44

how does cervical cerclage reduce the risk of preterm labour?

Answer 44

Cervical cerclage is an elective procedure that involves suturing around the cervix to provide mechanical support and keeps the cervix closed: • Usually done by 14 weeks gestation; vaginal approach or abdominal approach (rare) o Suture must be removed if labour occurs spontaneously or electively around 36+1 to 37+0 weeks

Question 45

what are the indications for cervical caclage?

Answer 45

history of 3 spontaneous preterm births or 2nd trimester losses or US finding of short cervix <25mm + history of PTL or 2nd trimester loss with singleton pregnancy

Question 46

what are the complcations of cervical caclage?

Answer 46

of membranes, bleeding, pregnancy loss (due to onset of labour, miscarriage process), bladder injury, anaesthetic risks (GA/spinal)

Question 47

how does progesterone reduce risk of PTL? How is it given (dosing?

Answer 47

Progesterone acts by inhibiting myometrial contractions & cervical ripening to reduce PTD and neonatal mortality & morbidity. weekly IM progesterone or daily PV progesterone

Question 48

what are the indications for progesterone to reduce risk of PTL?

Answer 48

asymptomatic women with a singleton pregnancy & cervical length <25mm in the mid trimester or women with previous preterm birth

Question 49

what is the optimum timing to start progesterone?

Answer 49

started at 16 – 20 weeks until 36 weeks

Question 50

Antenatal screening and treatment of bacterial vaginosis, trichomoniasis, candidiasis before ______________ may be beneficial in reducing PTL: • Using genital swabs & antibiotics

Answer 50

20 weeks gestation